oxytetracycline--anhydrous and Fish-Diseases

In recent years, feed additives have increasingly been adopted by the aquaculture industry. These supplements not only offer an alternative to antibiotics but have also been linked to enhanced growth performance. However, the literature is still limited and provides contradictory information on their effectiveness. This is mainly due to the wide variety of available products and their complex mechanisms of action. Phytogenic feed additives have been shown to have antimicrobial effects and can improve growth performance. In the present study, we investigated the susceptibility of several fish pathogenic bacteria to a phytogenic essential oil product in vitro. In addition, we determined the protective effect of a commercial phytogenic feed additive containing oregano, anis and citrus oils on the resistance of rainbow trout Oncorhynchus mykiss to infection by Aeromonas salmonicida. The bacterium was administered through 3 different routes: intra-peritoneal injection, immersion in a bacterial solution and cohabitation with infected fish. Mortality rates were significantly lower in infected rainbow trout that had received the feed additive: the overall mortality rate across all routes of infection was 18% in fish fed a diet containing the additive compared to 37% in fish that received unsupplemented feed. The route of infection also significantly impacted mortality, with average mortality rates of 60, 17.5 and 5% for intra-peritoneal injection, immersion and cohabitation, respectively. In general, fish were better protected against infection by immersion than infection by injection.

Topics: Aeromonas salmonicida; Animal Feed; Animals; Anti-Bacterial Agents; Chloramphenicol; Diet; Dietary Supplements; Drug Resistance, Bacterial; Fish Diseases; Food Additives; Gram-Negative Bacterial Infections; Oils, Volatile; Oncorhynchus mykiss; Oxytetracycline; Plant Oils; Specific Pathogen-Free Organisms

A large-scale mortality of larval and juvenile halibut Hippoglossus hippoglossus occurred at a semi-commercial halibut farm in Atlantic Canada. Investigation of the cause revealed aquareovirus particles in necrotic liver tissue of affected fish. Cytopathic effect on CHSE-214 cell lines occurred from all fish cultured for viruses, and the viral morphology of the particles in culture was consistent with that observed in necrotic host tissue. The virus was placed in the family of Reoviridae, genus Aquareovirus based on morphology and RT-PCR results. Multifocal hepatocellular necrosis was a consistent finding in all fish as well as acute necrosis of proximal renal tubules. Concurrent bacterial infections were present in some specimens. Fish experimentally treated with oxytetracycline or a combination of oxytetracycline and chloramine-T had a significantly lower mortality rate than untreated fish. Fish treated with chloramine-T alone had a significantly elevated mortality rate compared to controls. Despite supportive medical therapy, mortality levels in treated and untreated groups remained elevated, supporting the hypothesis that the primary pathogen was of viral origin. This is the first report of elevated mortalities in Atlantic halibut associated with an aquareovirus.

Topics: Animals; Anti-Bacterial Agents; Anti-Infective Agents, Local; Aquaculture; Bacterial Infections; Cells, Cultured; Chloramines; Drug Synergism; Fish Diseases; Flatfishes; Liver; Oxytetracycline; Reoviridae; Reoviridae Infections; Reverse Transcriptase Polymerase Chain Reaction; Tosyl Compounds

The presence of in-feed anti-sea lice drugs and their relationship with organic enrichment is poorly understood in sediment surrounding salmon farms. Using data from an aquaculture monitoring program (2018-2020), we describe this relationship at ten sites in four Canadian provinces. Three anti-sea lice pesticides (lufenuron, teflubenzuron, emamectin benzoate and metabolite desmethyl emamectin benzoate), and one antibiotic (oxytetracycline) were detected. Concentrations were often below limits of quantification. Values are also lower than those reported in other aquaculture salmon-producing countries. Highest concentrations, along with organic enrichment, were observed ~200 m of cages with lower concentrations detected up to 1.5 km away. Most samples had at least two drugs present: 75.2 % (British Columbia), 91.4 % (Newfoundland), and 54.8 % (New Brunswick/Nova Scotia) highlighting the potential for cumulative effects. Emamectin benzoate and oxytetracycline were detected four and three years respectively after last known treatments, demonstrating the need for research on overall persistence of compounds.

Topics: Animals; Anti-Bacterial Agents; Aquaculture; British Columbia; Copepoda; Fish Diseases; Geologic Sediments; Oxytetracycline; Salmo salar

The giant snakehead, Channa micropeltes, is an increasingly important economic freshwater fish in Thailand and other regions of Asia. Presently, giant snakehead are cultured under intensive aquaculture conditions, leading to high stress and conditions favouring disease. In this study, we reported a disease outbreak in farmed giant snakehead with a cumulative mortality of 52.5%, continuing for 2 months. The affected fish exhibited signs of lethargy, anorexia and haemorrhage of the skin and eyes. Further bacterial isolations revealed two different types of colonies on tryptic soy agar: small white, punctate colonies of gram-positive cocci and cream-coloured, round and convex colonies of rod-shaped gram-negative bacteria. Additional biochemical and species-specific PCR analysis based on 16S rRNA confirmed the isolates as Streptococcus iniae and Aeromonas veronii. Multilocus sequence analysis (MLSA) placed the S. iniae isolate into a large clade of strains from clinically infected fish worldwide. Gross necropsy findings showed liver congestion, pericarditis and white nodules in the kidney and liver. Histologically, the affected fish showed focal to multifocal granulomas with inflammatory cell infiltration in kidney and liver, enlarged blood vessels with mild congestion within the meninges of the brain and severe necrotizing and suppurative pericarditis with myocardial infarction. Antibiotic susceptibility tests revealed that S. iniae was sensitive to amoxicillin, erythromycin, enrofloxacin, oxytetracycline, doxycycline and resistant to sulfamethoxazole-trimethoprim, while the A. veronii was susceptible to erythromycin, enrofloxacin, oxytetracycline, doxycycline, sulfamethoxazole-trimethoprim and resistant to amoxicillin. Conclusively, our findings highlighted the natural concurrent bacterial infections in cultured giant snakehead, which support the implementation of appropriate treatment and control strategies.

Topics: Aeromonas; Aeromonas veronii; Amoxicillin; Animals; Doxycycline; Enrofloxacin; Erythromycin; Fish Diseases; Fishes; Oxytetracycline; Pericarditis; RNA, Ribosomal, 16S; Streptococcus iniae; Sulfamethoxazole; Thailand; Trimethoprim

Outbreaks of infections by Francisella orientalis represent one of the main obstacles to Nile tilapia (Oreochromis niloticus L.) farming. It is responsible for acute mortality in fingerlings and juveniles. The main control measure available is oral antibiotic therapy. This study compared the therapeutic efficacy of the antibiotics enrofloxacin and oxytetracycline, the most commonly used antimicrobial, against francisellosis in juvenile Nile tilapia (O. niloticus). Fish were challenged with a virulent isolate of F. orientalis and treated with medicated feed containing one of two doses of oxytetracycline (100 or 300 mg/kg of live weight (LW)) or 10 mg/kg of LW of enrofloxacin. The positive and negative control groups received feed without antibiotics; the negative control group was unchallenged. The results showed that enrofloxacin at a dose of 10 mg/kg of LW is effective against francisellosis in juvenile Nile tilapia (O. niloticus). Treatment with oxytetracycline did not eliminate the pathogen from the infected host, and the surviving fish became carriers. Enrofloxacin was able to cure the fish of infection with F. orientalis. This study suggests that enrofloxacin is a better option for treating francisellosis in Nile tilapia (O. niloticus L.). It controls mortality and avoids the carrier state in the fish, thus reducing the possibility of recurrence in the affected batches.

Topics: Animals; Anti-Bacterial Agents; Cichlids; Enrofloxacin; Fish Diseases; Francisella; Gram-Negative Bacterial Infections; Oxytetracycline

The rapid growth and intensification of aquaculture industries have led to an increased use of antibiotics. Consequently, growing concerns have mounted over the environmental contamination of these drugs from medicated feeds and the risk that this poses for antimicrobial resistance. To circumvent environmental leaching, farmers topcoat medicated feeds with oil; however, this only partially addresses the issue. This study investigated the potential of food-grade pregelatinized corn starch (PGS) as a second top-coating agent to reduce oxytetracycline (OTC) leaching from the hand-mixed medicated feed. We immersed top-coated medicated feeds for different periods of time and measured the concentration of OTC in the water to determine leaching. We found a significantly lower level of OTC in water samples collected from the PGS-coated medicated feed compared to the non-PGS-coated medicated feed, with concentrations of OTC approximately 4 and 2.6 times the latter after 5 min and 2 h of water immersion, respectively. We also fed PGS-coated antibiotic feed to jade perch to determine if fish accepted the top-coating and whether they absorbed the OTC. Results from a feeding trial suggested no difference in palatability between PGS and non-PGS-coated medicated feed. We also found that muscle tissue from fish fed with the aforementioned diets had similar levels of OTC concentrations, suggesting that PGS coating does not alter the gastrointestinal absorption of this medication. From our experiment, we conclude that PGS is potentially a new top-coating agent to reduce leaching in hand-mixed OTC medicated feed.

Topics: Animal Feed; Animals; Anti-Bacterial Agents; Fish Diseases; Oxytetracycline; Perches; Starch; Water

Many governments have approved the use of oxytetracycline as an antibiotic additive to food fish, with oxytetracycline now routinely used in many nations. However, oxytetracycline is known to have immunosuppression impacts. We, therefore, evaluated the immunological, antioxidative, and histopathological status of Nile tilapia fed a diet containing silymarin (100 mg/kg fish feed) for 0, 2, 4, 6, and 8 weeks. The protective effects of silymarin against Aeromonas hydrophila (A. hydrophila) infection and oxytetracycline treatment were evaluated. Blood parameters (erythrocyte count, white blood cell count, hemoglobin, and packed cell volume) improved over time in fish fed on dietary silymarin. Serum levels of alanine aminotransferase (ALT) were lower in fish fed on dietary silymarin, whereas serum levels of aspartate transferase (AST)and alkaline phosphatase (ALK) were unchanged. Dietary silymarin affected serum lipid profiles as decreases in serum triglyceride and low-density lipoprotein cholesterol levels and a trend toward lower cholesterol levels, whereas serum high-density lipoprotein cholesterol levels were increased compared to fish fed on the control diet. Dietary silymarin resulted in an increase of serum total protein levels and globulin fractions. Significant and progressive increases in catalase and glutathione peroxidase levels were observed after six weeks of feeding on a dietary silymarin before decreasing to control levels at the end of the experimental period. Fish fed on dietary silymarin, interleukin-1 and fish tumor necrosis factor-alpha were upregulated in hepatic tissues; however, interleukin-10 levels decreased to comparable levels to controls after eight weeks. Fish infected with A. hydrophila displayed septicemia (opaque eye, hemorrhagic ulcers, dentated fins, hepatomegaly, and splenomegaly). Reduced mortality was observed in Nile tilapia infected with A. hydrophila and fed a diet containing silymarin, indicating that silymarin improves fish responses to oxytetracycline with a 37% reduction in mortality.

Topics: Aeromonas hydrophila; Animal Feed; Animals; Cholesterol; Cichlids; Diet; Dietary Supplements; Fish Diseases; Gram-Negative Bacterial Infections; Oxytetracycline; Silymarin

Topics: Animals; Anti-Bacterial Agents; Chile; Fish Diseases; Fisheries; Flavobacteriaceae Infections; Oxytetracycline; Salmonidae; Tenacibaculum; Thiamphenicol

This study was conducted to examine the combinatory effects of β-glucan and oxytetracycline (OTC) on hybrid giant tiger groupers (Epinephelus fuscoguttatus × Epinephelus lanceolatus). In vitro tests, OTC significantly reduced superoxide anion production and phagocytic activity in primary head kidney leukocytes. However, this suppressive effect was alleviated by co-treatment with β-glucan. Subsequently, feeding trials were performed to investigate the potential immunomodulatory effects of dietary β-glucan alone or in combination with OTC on groupers. A total of 210 healthy groupers (368.00 ± 51.03 g) were divided into six groups. Group 1 was the control group, group 2 (BG) received 5 g β-glucan per kg feed weight, groups 3-5 received 5 g/kg β-glucan in combination with 10, 30, or 50 mg OTC/kg fish weight/day (groups M1, M2, and M3, respectively), and group 6 (O) received 50 mg OTC/kg fish weight/day. Fish were sampled to determine the innate immunity parameters and residual OTC levels in the muscle tissue during a 28-day feeding regimen. Residual OTC levels were considerably higher in groups M3 and O compared with the other groups, and peaked on day 14. This was followed by a slight decrease on day 28, despite a continuous supply of OTC. Notably, fish fed with OTC alone had significantly decreased phagocytic rates and superoxide anion production observed in head kidney leukocytes, as well as poorer protection against Vibrio alginolyticus infection. These immunosuppressive effects were not observed in the fish fed with β-glucan in combination with a lower dose of OTC (group M2). Thus, these data suggest that the combination of dietary β-glucan and OTC exerts synergistic immunostimulating effects that protect groupers from bacterial infection.

Topics: Animal Feed; Animals; Bass; beta-Glucans; Chimera; Dietary Supplements; Fish Diseases; Head Kidney; Immunity, Innate; Immunosuppressive Agents; Leukocytes; Oxytetracycline; Phagocytosis; Vibrio alginolyticus; Vibrio Infections

In Egypt, Nile tilapia represents the main cultured type due to its economical price, palatability and easy culturing. This study was aimed to elucidate the pathogenicity of V. alginolyticus isolated from diseased sea bass and experimentally infected healthy Nile tilapia fish.. Healthy Nile tilapia fish were injected I/P with V. alginolyticus isolated from diseased sea bass. Symptoms and mortality rates of infected Nile tilapia fish were recorded during the experimental period. Re-isolation of V. alginolyticus was done from infected tilapia fish by bacteriological methods. For confirmation the pathogenicity of Vibrio isolated either from marine fish or tilapia fish, PCR test was done using tdh and bla gens. Liver and kidney function tests with histopathological examinations of some organs were performed. Treatment trial was done according to the antibiotic sensitivity test.. The isolated Vibrio is highly pathogenic to Nile tilapia fish causing deterioration in all parameters which finished by severe mortalities. Treatment with florfenicol, enrofloxacin, or oxytetracycline reduced the mortality rate and improved liver and kidney function parameters of infected Nile tilapia fish.. V. alginolyticus can infect both marine and fresh water fish inducing a high mortality rate. Treatment of infected fish with florfenicol, enrofloxacin, or oxytetracycline reduces the mortality rate.

Topics: Animals; Anti-Bacterial Agents; Aquaculture; Bass; Cichlids; Enrofloxacin; Fish Diseases; Oxytetracycline; Thiamphenicol; Vibrio alginolyticus; Vibrio Infections

The aetiological agent of Piscirickettsiosis is Piscirickettsia salmonis, a Gram-negative intracellular pathogen, and high doses of antibiotics have regularly been employed to treat this infection. Seven florfenicol and/or oxytetracycline resistance genes (tet pump, tetE, Tclor/flor, Tbcr, TfloR, ompF and mdtN) were identified in strains by in silico genome analyses. Later, the number of single nucleotide polymorphisms (SNPs) and its relationship with the resistance to these antibiotics were identified and analysed, using the original LF-89 strain as reference. Trials to determine and compare the minimum inhibitory concentration (MIC) of oxytetracycline and florfenicol in each strain, as well as to quantify the gPCR transcripts levels in the selected genes, were performed. Therefore, variations in the resistance to both antibiotics were observed, where the strain with fewer SNPs showed the highest susceptibility. Consistently, the in silico 3D analyses of proteins encoded by the selected genes revealed structural changes, evident in the sequences with the highest number of SNPs. These results showed that the bacterial resistance to oxytetracycline was mainly linked to the presence of SNPs in relevant sites, antibiotic resistance genes and an OmpF porin, leading to important changes in the protein structure.

Topics: Animals; Drug Resistance, Microbial; Fish Diseases; Genes, Bacterial; Microbial Sensitivity Tests; Oxytetracycline; Piscirickettsia; Piscirickettsiaceae Infections; Polymorphism, Single Nucleotide; Thiamphenicol

The mucosal surfaces of fish harbour microbial communities that can act as the first-line of defense against pathogens. Infectious diseases are one of the main constraints to aquaculture growth leading to huge economic losses. Despite their negative impacts on microbial diversity and overall fish health, antibiotics are still the method of choice to treat many such diseases. Here, we use 16 rRNA V4 metataxonomics to study over a 6 week period the dynamics of the gill and skin microbiomes of farmed seabass before, during and after a natural disease outbreak and subsequent antibiotic treatment with oxytetracycline. Photobacterium damselae was identified as the most probable causative agent of disease. Both infection and antibiotic treatment caused significant, although asymmetrical, changes in the microbiome composition of the gills and skin. The most dramatic changes in microbial taxonomic abundance occurred between healthy and diseased fish. Disease led to a decrease in the bacterial core diversity in the skin, whereas in the gills there was both an increase and a shift in core diversity. Oxytetracycline caused a decrease in core diversity in the gill and an increase in the skin. Severe loss of core diversity in fish mucosae demonstrates the disruptive impact of disease and antibiotic treatment on the microbial communities of healthy fish.

Topics: Animals; Anti-Bacterial Agents; Aquaculture; Bass; Disease Outbreaks; Fish Diseases; Gills; Gram-Negative Bacterial Infections; Microbiota; Oxytetracycline; Photobacterium; Skin

This study was carried out to evaluate the potential antibacterial and immunomodulatory effects of the dietary acidifier propionic acid (PA) when given alone or in combination with oxytetracycline (OTC) on Nile tilapia (Oreochromis niloticus). Apparently healthy O. niloticus (n = 240; 52 ± 3.75 g) were randomly allocated into four equal groups (n = 60/group): control group fed a basal diet alone and the other three groups fed basal diets supplemented with either PA (200 mg /kg of diet, PA group) or OTC (500 mg/kg of diet, OTC group) alone or in combination (PA + OTC group). Each group was subdivided into two subgroups (n = 30/subgroup, each subgroup had triplicate of 10 fish); subgroup (A) was used to evaluate the antibacterial effects with the aforementioned 2 weeks feeding regime, and subgroup (B) was used to evaluate the immunomodulatory effects against Aeromonas hydrophila infection with similar 2 weeks feeding regime. Among the four groups, PA + OTC group showed the highest significant (p < 0.0001) antibacterial activity as indicated by widest inhibition zones against A. hydrophila and lowest total gastrointestinal bacterial counts. Additionally, this group had the best immunomodulatory effect as noticed by a significant (p < 0.05) increase in total serum protein, globulin, IgM, phagocytic activity and index, lysosome activity, and significant (p < 0.05) upregulation in the expression levels of immunity-related genes (MHC I, MHC IIA, MHC IIB, Tlr7, IgM heavy chain, TNFα, and IL1β) in head-kidney. Notably, the combined dietary PA and OTC improved the hematological parameters and reduced the oxidative damage of hepatopancreas and head-kidney induced by OTC. This data suggests dietary PA as potential adjuvant to OTC in O. niloticus diets to get maximal antibacterial and immunomodulatory effects.

Topics: Aeromonas hydrophila; Animal Feed; Animals; Anti-Bacterial Agents; Cichlids; Diet; Dietary Supplements; Fish Diseases; Gene Expression Regulation; Gram-Negative Bacterial Infections; Immunologic Factors; Kidney; Liver; Oxytetracycline; Phagocytosis; Propionates

Leakage of medical residues into the environment can significantly impact natural communities. For example, antibiotic contamination from agriculture and aquaculture can directly influence targeted pathogens, but also other non-targeted taxa of commensals and parasites that regularly co-occur and co-infect the same host. Consequently, antibiotics could significantly alter interspecific interactions and epidemiology of the co-infecting parasite community. We studied how minor environmental concentrations of antibiotic affects the co-infection of two parasites, the bacterium Flavobacterium columnare and the fluke Diplostomum pseudospathaceum, in their fish host. We found that antibiotic in feed, and particularly the minute concentration in water, significantly decreased bacterial virulence and changed the infection success of the flukes. These effects depended on the level of antibiotic resistance of the bacterial strains. Antibiotic, however, did not compensate for the higher virulence of co-infections. Our results demonstrate that even very low environmental concentrations of antibiotic can influence ecology and epidemiology of diseases in co-infection with non-targeted parasites. Leakage of antibiotics into the environment may thus have more complex effects on disease ecology than previously anticipated.

Topics: Animals; Anti-Bacterial Agents; Aquaculture; Coinfection; Drug Resistance, Bacterial; Fish Diseases; Flavobacteriaceae Infections; Flavobacterium; Oncorhynchus mykiss; Oxytetracycline; Trematoda; Trematode Infections; Virulence; Water Pollution, Chemical

Oxytetracycline (OTC) is commonly employed in fish farms to prevent bacterial infections in China, and because of their widely and intensive use, the potential harmful effects on organisms in aquatic environment are of great concern. Ciliates play an important role in aquatic food webs as secondary producers, and Pseudocohnilembus persalinus, is one kind of them which are easily found in fish farms, surviving in polluted water. Therefore, using P. persalinus as experimental models, this study investigated the effects of oxytetracycline (OTC) on the growth, antioxidant system and morphological damage in pollution-resistant ciliates species. Our results showed that the 96-h EC

Topics: Animals; Bacterial Infections; Fish Diseases; Gene Expression Regulation; Oligohymenophorea; Oxidative Stress; Oxytetracycline; Protozoan Proteins; Superoxide Dismutase

Piscirickettsia salmonis is the pathogen causing Piscirickettsiosis. For treatment, the industry mainly uses oxytetracycline and florfenicol, so it is essential to understand the degree of susceptibility of this pathogen to these drugs. But this is still unknown for a large number of P. salmonis strains, as are the molecular mechanisms responsible for greater or lesser susceptibility. However, genes that confer resistance to these antimicrobials have been reported and characterized for this and other bacterial species, among which are membrane proteins that take out the drug. Our results identified differences in the degree of susceptibility to both antibiotics among different Chilean isolated of these bacteria. We analysed 10 available genomes in our laboratory and identified ~140 genes likely to be involved in antibiotic resistance. We analysed six specific genes, which suggests that some of them would eventually be relevant in conferring resistance to both antibiotics, as they encode for specific transporter proteins, which increase the number of transcripts when grown in media with these antibiotics. Our results were corroborated with EtBr permeability analysis, which revealed that the LF-89 strain accumulates this compound and has a reduced capacity to expulse it compared with the field strains.

Topics: Animals; Anti-Bacterial Agents; Chile; Drug Resistance, Bacterial; Fish Diseases; Oxytetracycline; Piscirickettsia; Piscirickettsiaceae Infections; Thiamphenicol

An 8-week feeding trial was conducted to evaluate the effects of dietary probiotics on growth performance and non-specific immune responses in starry flounder, Platichthys stellatus. Fish averaging 46.5 ± 0.65 g (mean ± SD) were fed one of the six experimental diets; one control (Cont), and five other diets were prepared by supplementing single-probiotics 1 (Bacillus subtilis; SP

Topics: Animal Feed; Animals; Anti-Infective Agents; Aspergillus oryzae; Bacillales; Blood Chemical Analysis; Diet; Disease Resistance; Edwardsiella tarda; Enterobacteriaceae Infections; Fish Diseases; Flounder; Oxytetracycline; Probiotics; Random Allocation; Saccharomyces cerevisiae

Topics: Animals; Anti-Bacterial Agents; Fish Diseases; Fluorescent Antibody Technique, Indirect; Microbial Sensitivity Tests; Oncorhynchus mykiss; Oxytetracycline; Piscirickettsia; Piscirickettsiaceae Infections; Polymerase Chain Reaction; Salmo salar; Thiamphenicol

Topics: Animals; Anti-Bacterial Agents; Brazil; Carrier State; Cichlids; Fish Diseases; Microbial Sensitivity Tests; Oxytetracycline; Streptococcal Infections; Streptococcus agalactiae

Edwardsiellosis is one of the most important bacterial diseases in eels. Edwardsiella tarda (E. tarda) isolates (n=94) from diseased eels were screened against the eight most commonly used antimicrobial agents in aquaculture in Taiwan. These isolates were highly susceptible to ampicillin, amoxicillin, florfenicol, oxolinic acid and flumequine. In total, 20 of the 94 (21.3 per cent) isolates tested were resistant to oxytetracycline (OTC). Among the 20 tetracycline-resistant E. tarda isolates, tet(A) was the predominant resistance determinant and was detected in 100 per cent of the isolates, whereas 90 per cent of these isolates carried the tet(M) determinant. The efflux pump inhibitor omeprazole reduced the minimum inhibitory concentrations (MICs) of OTC for these isolates by twofold to eightfold, suggesting that an intact efflux pump, presumably encoded by tet(A), is required for high-level tetracycline resistance. Real-time PCR experiments showed that increased expression levels of tet(A) and tet(R) could contribute to OTC resistance. Southern blot hybridisation also confirmed that the 20 OTC-resistant E. tarda isolates all carried the TetA determinant on a plasmid that is approximately 50 or 70 kb in size, and restriction fragment length polymorphisms (RFLP) showed that the tet(A) gene was located on an 8-10 kb EcoRI fragment in all of these plasmids. The same plasmid type and RFLP patterns were detected across different farms in the same region, but differences in their pulsed-field gel electrophoresis (PFGE) patterns were observed. This suggests a possible role for horizontal spreading and local transmission of the plasmid in the OTC-resistant E. tarda population of eels from two different geographic origins.

Topics: Animals; Edwardsiella tarda; Eels; Enterobacteriaceae Infections; Fish Diseases; Oxytetracycline; Taiwan; Tetracycline Resistance

The present study aimed to determine oxytetracycline (OTC), florfenicol (FLO) and oxolinic acid (OXO) MICs and zone diameters for 24 Chilean Vibrio ordalii isolates using the methods for broth dilution susceptibility testing of bacteria isolated from aquatic animals and the methods for antimicrobial disk susceptibility testing of bacteria isolated from aquatic animals guidelines published by the Clinical Laboratory Standards Institute (CLSI). The results were then used in a normalized resistance interpretation (NRI) analysis to establish tentative laboratory-specific epidemiological cut-off (ECOFF) values. MIC results were similar at the two tested temperatures (22 °C and 18 °C). At 18 °C, the NRI analysis of OTC, FLO and OXO MIC data calculated laboratory-specific ECOFF values and non-wild-type (NWT) rates to be ≤4 mg/l (24%), ≤16 mg/l (4%) and ≤8 mg/l (25%), respectively. Tests performed with all V. ordalii isolates following the officially recommended incubation temperature (22 °C) revealed difficulties in measuring inhibition zone diameters. When disk diffusion tests were performed using Mueller-Hinton agar with 1% NaCl (MHA-1) at 18 °C the inhibition zone diameter distributions showed the formation of WT populations which could be defined using NRI analysis. For OTC the laboratory-specific ECOFF value was ≥38 mm with NWT rate of 16.7%. For FLO and OXO, the laboratory-specific ECOFF values were ≥38 and ≥40, respectively, generating NWT rates of 25 and 46%, respectively. Although the CLSI suggests testing Vibrio spp. on MHA-1 at 22 °C, we found measurements of the 24 isolates were better defined and normally distributed at 18 °C. This is the first study determining the MIC and disk diffusion test of V. ordalii isolated from diseased salmonids, where laboratory-specific ECOFF values could be established. Also resistance to OTC, FLO and OXO among some Chilean isolates was demonstrated.

Topics: Animals; Anti-Bacterial Agents; Fish Diseases; Microbial Sensitivity Tests; Oxolinic Acid; Oxytetracycline; Thiamphenicol; Vibrio; Vibrio Infections

The excessive use of antibiotics in aquaculture can adversely affect not only the environment, but also fish themselves. In this regard, there is evidence that some antibiotics can activate the immune system and reduce their effectiveness. None of those studies consider in detail the adverse inflammatory effect that the antibiotic remaining in the water may cause to the fish. In this work, we use the zebrafish to analyze quantitatively the effects of persistent exposure to oxytetracycline, the most common antibiotic used in fish farming.. We developed a quantitative assay in which we exposed zebrafish larvae to oxytetracycline for a period of 24 to 96 hrs. In order to determinate if the exposure causes any inflammation reaction, we evaluated neutrophils infiltration and quantified their total number analyzing the Tg(mpx:GFP)(i114) transgenic line by fluorescence stereoscope, microscope and flow cytometry respectively. On the other hand, we characterized the process at a molecular level by analyzing several immune markers (il-1β, il-10, lysC, mpx, cyp1a) at different time points by qPCR. Finally, we evaluated the influence of the inflammation triggered by oxytetracycline on the regeneration capacity in the lateral line.. Our results suggest that after 48 hours of exposure, the oxytetracycline triggered a widespread inflammation process that persisted until 96 hours of exposure. Interestingly, larvae that developed an inflammation process showed an improved regeneration capacity in the mechanosensory system lateral line.

Topics: Animals; Animals, Genetically Modified; Anti-Bacterial Agents; Biomarkers; Fish Diseases; Inflammation; Oxytetracycline; Regeneration; Zebrafish

Lancefield group C Streptococcus dysgalactiae is an emerging fish pathogen, which was first isolated in 2002 in Japan. Streptococcus dysgalactiae isolates collected from diseased fish in Japan (n=12), Taiwan (n=12), China (n=2), Malaysia (n=3), and Indonesia (n=1) were characterized using biased sinusoidal field gel electrophoresis (BSFGE), sodA gene sequence analysis, and antimicrobial susceptibility. These isolates exhibited high phenotypic homogeneity irrespective of the countries from where the strains were collected. Seventeen isolates were found to be resistant to oxytetracycline and carried the tet(M) gene, except for the strains collected in Taiwan and the PP1564 strain collected in China. The sodA gene sequence analysis revealed that 23 isolates were identical, except for one Japanese isolate (KNH07902), in which a single nucleotide differed from that of the other isolates. Based on BSFGE typing by ApaI macrorestriction, the isolates - including the Japanese, Taiwanese, and Chinese isolates - could be grouped into one main cluster at a 70% similarity level. However, the macrorestriction genotypes of some isolates were apparently distinct from those of the main cluster.

Topics: Animals; Anti-Bacterial Agents; Asia, Eastern; Asia, Southeastern; Bacterial Proteins; DNA, Bacterial; Drug Resistance, Bacterial; Fish Diseases; Genetic Variation; Genome, Bacterial; Oxytetracycline; Perciformes; Phylogeny; Sequence Analysis, DNA; Smegmamorpha; Streptococcal Infections; Streptococcus; Superoxide Dismutase

The effect of oxytetracycline (OTC) treatment on intestinal bacterial populations in juvenile Atlantic salmon Salmo salar was evaluated. Oxytetracycline was administered by way of medicated feed to fish held in experimental tanks. Restriction fragment length polymorphism and sequencing of 16S rDNA from isolates were used to analyze the intestinal microbiota before, during, and after OTC administration. The microbiota from untreated fish was more diverse, consisting mainly of Pseudomonas, Acinetobacter, Bacillus, Flavobacterium, Psycrobacter, and Brevundimonas spp. In contrast, the microbiota of the OTC-treated group was characterized by lower diversity and consisted only of Aeromonas, clustering with A. sobria and A. salmonicida. Antibiotic-resistant isolates were identified as Aeromonas spp.; sequencing the resistance determinant showed it to be the tetE gene. Overall, OTC treatment changed the composition of the intestinal microbiota of Atlantic salmon, as evidenced by a reduction in bacterial diversity. These results support the current concern that antibiotic treatment can facilitate the proliferation of opportunistic bacteria by eradicating competing microorganisms.

Topics: Aeromonas; Animal Feed; Animals; Anti-Bacterial Agents; Bacteria; Biodiversity; Colony Count, Microbial; DNA, Bacterial; DNA, Ribosomal; Drug Resistance, Bacterial; Fish Diseases; Gastrointestinal Tract; Microbial Sensitivity Tests; Oxytetracycline; Polymorphism, Restriction Fragment Length; RNA, Ribosomal, 16S; Salmo salar

Soyabean meal (SBM)-induced enteritis in the distal intestine of the teleost Atlantic salmon (Salmo salar L.) and other salmonids may be considered a model for diet-related mucosal disorders in other animals and man. The role of the intestinal microbiota in its pathogenesis was explored. Compared to diets containing fishmeal (FM) as the sole protein source, responses to extracted SBM or the prebiotic inulin, with or without oxytetracycline (OTC) inclusion, were studied following a 3-week feeding trial. Intestinal microbiota, organosomatic indices and histology, as well as immunohistochemical detection of proliferating cell nuclear antigen (PCNA), heat shock protein 70 (HSP70) and caspase-3-positive cells in the distal intestine, were studied. Distal intestine somatic indices (DISI) were higher in inulin and lower in SBM compared to FM-fed fish. The low DISI caused by SBM corresponded with histological changes, neither of which was affected by OTC, despite a significant decrease in adherent bacteria count. Image analysis of PCNA-stained sections showed a significant increase in the proliferative compartment length in SBM-fed fish, accompanied by apparent increases in reactivity to HSP70 and caspase-3 along the mucosal folds, indicating induction of cellular repair and apoptosis, respectively. Fish fed the SBM diet had higher total number as well as a more diverse population composition of adherent bacteria in the distal intestine. Thus SBM-induced enteritis is accompanied by induction of distal intestinal epithelial cell protective responses and changes in microbiota. Putative involvement of bacteria in the inflammatory response merits further investigation.

Topics: Animals; Apoptosis; Bacteria; Body Constitution; Caspase 3; Cell Proliferation; Diet; Enteritis; Fish Diseases; Fishes; Glycine max; HSP70 Heat-Shock Proteins; Intestinal Mucosa; Intestines; Inulin; Oxytetracycline; Probiotics; Proliferating Cell Nuclear Antigen; Salmo salar

A method was optimised and validated for simultaneous monitoring of several drugs of different classes of antibiotics such as quinolones (oxilinic acid and flumequine), tetracyclines (oxytetracycline), sulfonamides (sulfadiazine) and trimethoprim in fish muscle and skin. The method is based on solid-liquid extraction without further sample clean up followed by liquid chromatography-mass spectrometry (LC-MS) determination with electrospray ion source (ESI) in positive mode. The limits of quantification (LOQs) were lower than 20 microg/kg for all compounds and repeatability, expressed as relative standard deviations (RSD), were lower than 15%. Therefore, the LC-MS method was successfully applied for the quantitative determination of antibiotics in gilthead sea bream muscle and skin and oxytetracycline in medicated fishes.

Topics: Animals; Anti-Bacterial Agents; Chromatography, High Pressure Liquid; Drug Residues; Fish Diseases; Fishes; Molecular Structure; Muscles; Oxytetracycline; Quinolones; Reference Standards; Reproducibility of Results; Sea Bream; Sensitivity and Specificity; Solid Phase Extraction; Spectrometry, Mass, Electrospray Ionization; Sulfonamides; Tandem Mass Spectrometry; Tetracyclines; Trimethoprim; Veterinary Drugs

Topics: Animals; Anti-Bacterial Agents; DNA, Bacterial; Fish Diseases; Flavobacteriaceae Infections; Flavobacterium; Oncorhynchus mykiss; Oxytetracycline; Polymerase Chain Reaction; Scotland; Water Microbiology

Topics: Animals; Arkansas; Bass; Chlamydia; Chlamydia Infections; Disease Outbreaks; Dose-Response Relationship, Drug; Epithelial Cells; Fish Diseases; Gills; Kidney; Oxytetracycline

Columnaris disease was induced in channel catfish, Ictalurus punctatus (Rafinesque), by bath exposure to four highly virulent isolates of Flavobacterium columnare. In untreated controls, mortality began 20 h after exposure and reached 100% by 48 h. Mortality in channel catfish given antibiotic treatments with oxytetracycline or a combination of sulphadimethoxine and ormetoprim in feed prior to bacterial challenge was zero with all four strains of F. columnare. Diquat (Zeneca Agricultural Products, Wilmington, DE, USA) was the most effective bath treatment; mortality with all four strains was zero. With potassium permanganate, chloramine-T, hydrogen peroxide and copper sulphate, bath treatment efficacy varied significantly among strains (P = 0.0346) and among treatments (P = 0.0033). Bath treatments with chloramine-T and potassium permanganate significantly reduced (P < 0.05) mortality from 100 to 75 and 69%, respectively, but copper sulphate and hydrogen peroxide treatments were not effective. Based on our results, oral antibiotics prevented columnaris disease but, of the bath treatments, only Diquat produced a dramatic reduction in the mortality of acutely infected fish. Diquat is labelled for aquatic use as an herbicide in the USA but in large ponds it is prohibitively expensive.

Topics: Animals; Anti-Bacterial Agents; Aquaculture; Catfishes; Chloramines; Copper Sulfate; Fish Diseases; Flavobacteriaceae Infections; Flavobacterium; Oxytetracycline; Potassium Permanganate; Pyrimidines; Sulfadimethoxine; Tosyl Compounds

The antimicrobial agents used to treat bacterial fish diseases are archaic, and their uses may result in the emergence of drug-resistant bacterial strains. This study evaluated the in vitro antimicrobial activity of combinations of Tricide and neomycin or oxytetracycline on common disease-causing bacteria of fish and its possible use as an alternative treatment of these diseases. Tricide solutions containing of 8 mM United States Pharmacopeia (USP) disodium ethylenediaminetetraacetate dehydrate (chelator) and 20 mM USP 2-amino-2-hydroxymethyl-1,3-propanediol (buffer) potentate the antimicrobial action of neomycin and oxytetracycline when reacted in vitro with Aeromonas hydrophila, Streptococcus iniae, Pseudomonas aeruginosa, and Staphylococcus aureus. Serial passage of the test organisms in Tricide or Tricide and neomycin or oxytetracycline did not result in the development of resistant forms. Combinations of Tricide and neomycin or oxytetracycline reduced the amount of antibiotics necessary for fish therapy, render drug-resistant bacteria sensitive to antimicrobial therapy, may be used to decontaminate recently shipped fish, and should reduce the formation of antibiotic-resistant forms.

Topics: Animals; Anti-Bacterial Agents; Bacteria; Bacterial Infections; Buffers; Chelating Agents; Dose-Response Relationship, Drug; Edetic Acid; Fish Diseases; Fishes; Hydrogen-Ion Concentration; In Vitro Techniques; Microbial Sensitivity Tests; Neomycin; Oxytetracycline; Propylene Glycols

In 1994, tilapia (Oreochromis mossambicus and Sarotherodon melanotheron) in wild and farmed populations on Oahu, Hawaii, USA, began to die of an unknown disease that was similar but not identical to piscirickettsiosis in salmonids. Only tilapia were affected. Diseased tilapia often swam erratically and had trouble staying at depth. Scattered cutaneous haemorrhage and exophthalmia were often noted. In many cases, fish were found dead with no clinical signs. Gills exhibited epithelial hyperplasia with severe multifocal consolidation of secondary lamellae. Multiple granulomas were observed in the gills, spleen, kidney, choroid gland and testes, but not in the liver. Tilapia mortalities occurred only during the cooler months (October to April) of the year and were not recorded during the warmer months (May to September). The mortalities declined with each successive year, after the 1994 outbreak, and currently losses are sporadic. Oxytetracycline-medicated feed reduced mortality. Cytologic examination of blood smears revealed moderate to large numbers of Gram-negative, pleomorphic, intracellular bacteria in rare circulating monocytes. Histologically, some predilection for nervous tissue and brain was observed. When viewed with transmission electron microscopy, pleomorphic coccoid bacteria, measuring 0.56 +/- 0.14 x 0.7 +/- 0.20 microm, occurred free in the cytoplasm and within phagolysosomes. The organisms had a double cell wall, no defined nucleus and variable electron-dense and -lucent areas. Unlike Piscirickettsia salmonis, the agent of piscirickettsiosis, the Hawaiian tilapia Piscirickettsia-like organism (HTPLO) does not form craterform lesions in the liver and is active above 20 degrees C. HTPLO can be transmitted horizontally by cohabitation, and cold stress induces the syndrome in juvenile tilapia from farms where the disease is endemic.

Topics: Animals; Anti-Bacterial Agents; Aquaculture; Bacterial Infections; Disease Outbreaks; Fish Diseases; Gammaproteobacteria; Hawaii; Microscopy, Electron; Oxytetracycline; Seasons; Tilapia

A new oxytetracycline (OTC) resistance (Otc(r)) determinant, Tet 34, was cloned from chromosomal DNA of Vibrio sp. no. 6 isolated from intestinal contents of cultured yellowtail (Seriola quinqueradiata). The transformant, containing cloned Tet 34, could grow in broth containing 25 microg of drug per ml with 10 mM MgCl2. Tet 34 encoded an open reading frame (ORF) 154 amino acids long. The amino acid sequence of the ORF was homologous to sequences of several bacterial xanthine-guanine phosphoribosyltransferases (XPRTs), which act in purine nucleotide salvage synthesis. Mg2+ binding site residues and the active site were highly conserved in XPRT and the ORF of Tet 34. The results suggest that Tet 34 encodes a new Mg2+-dependent Otc(r) mechanism.

Topics: Amino Acid Sequence; Animals; Anti-Bacterial Agents; Aquaculture; Fish Diseases; Fishes; Intestines; Magnesium; Molecular Sequence Data; Oxytetracycline; Pentosyltransferases; Tetracycline Resistance; Vibrio; Vibrio Infections

A new virus disease that displays dermal ulceration and high mortality has been occurring since 1996 in color carp Cyprinus carpio reared in warm water in Japan. In histological examinations, initial erosive lesions displayed necrosis, hemorrhage and fibrin deposition in the dermal loose connective tissue and were accompanied by the partial destruction of the epidermis. Developed ulcerative lesions involved the lateral musculature with bacterial invasions. In visceral organs, necrotic cells were observed in the hematopoietic tissue, the spleen and the intestinal tissues as well as in cardiac muscle fibers which showed no signs of bacterial invasion. Electron microscopy revealed corona-like virus particles in these necrotic cells. The necrotic cells of the hematopoietic tissue and the spleen were accompanied by the formation of tubular structures and crystalline inclusions. The putative virus was isolated and cultured in epithelioma papillosum cyprini (EPC) cells. Carp experimentally inoculated with the cultured virus showed virus transmission, and the same pathological signs of the disease and mortalities as in natural infections.

Topics: Animals; Anti-Bacterial Agents; Carps; Coronaviridae Infections; Coronavirus; Cytopathogenic Effect, Viral; Disease Outbreaks; Fish Diseases; Histocytochemistry; Japan; Microscopy, Electron; Muscle, Smooth, Vascular; Oxytetracycline; Skin; Skin Ulcer; Spleen; Viremia; Virion

The minimum inhibitory concentration (MIC) was measured to evaluate the antibacterial activities of chloramphenicol (CP), thiamphenicol (TP) and florfenicol (FFC) against the aquatic bacterial isolates from soft-shell turtles, fish and shellfish. Amoxicillin (AMPC), oxytetracycline (OTC) and oxolinic acid (OA) were included to compare with above protein synthesis inhibitors. The results showed that the order of MIC range of the isolates from soft-shell turtles for tested drugs was OA>FFC, CP>TP> AMPC, OTC. The percentage of the resistant strains indicated that OA was the lowest (7.14%) and OTC was the highest (85.07%). The order of antibacterial activity against the isolates from fish was OA>FFC>CP>AMPC>OTC>TP. The percentage of the resistant strains revealed that OA (13.64%) and OTC (80.91%) were the lowest and the highest, respectively. For the isolates from shellfish, the order of antimicrobial activity was OA>CP, FFC>AMPC, OTC, TP. TP showed the greatest percentage of the resistant strains (58.7%), but that of OA was the lowest (4.35%). The most common resistant patterns of the isolates from turtles, fish and shellfish were AMPC-OTC, CP-TP-AMPC-OTC, and FFC-CP-TP-AMPC-OTC, respectively. There were partially-complete resistance of the resistant isolates among CP, TP and FFC. The findings indicated that previous treatment might affect the choice of drug to use for aquatic bacterial diseases.

Topics: Amoxicillin; Animals; Anti-Bacterial Agents; Anti-Infective Agents; Aquaculture; Bacteria; Chloramphenicol; Fish Diseases; Fishes; Microbial Sensitivity Tests; Oxolinic Acid; Oxytetracycline; Penicillins; Shellfish; Taiwan; Thiamphenicol; Turtles

The susceptibility of six Vibrio harveyi strains to antibiotics was studied. Four strains originally isolated from diseased penaeids and two reference strains originally isolated from either sea water (ATCC 25919) or diseased Talorchestia sp. (ATCC 14126) were used in the present study. Results revealed that all three strains isolated in Taiwan exhibited resistance against nitrofurantoin, novobiocin and sulphonamide. The two reference strains and the strain isolated in Indonesia were susceptible to these three antibiotics.

Topics: Animals; Anti-Bacterial Agents; Chloramphenicol; Ciprofloxacin; Decapoda; Doxycycline; Drug Resistance, Microbial; Erythromycin; Fish Diseases; Fishes; Microbial Sensitivity Tests; Nalidixic Acid; Nitrofurantoin; Novobiocin; Oxolinic Acid; Oxytetracycline; Penicillins; Seawater; Streptomycin; Sulfonamides; Vancomycin; Vibrio; Vibrio Infections; Water Microbiology

The choice of antibacterial drugs for the treatment of bacterial diseases in farmed salmonids changed dramatically during the period 1980-1994. In terms of treatment doses, oxytetracycline chloride was the most frequently prescribed antibacterial drug during the periods 1980-1983 and 1985-1986. In 1984, prescriptions changed in favour of furazolidone and trimethoprim/ sulphadiazine (1:5). Oxolinic acid was introduced for use in farmed fish in Norway in 1987, and immediately became the drug of choice, comprising 36% and 50% of the prescribed treatment doses in 1987 and 1988, respectively. In 1989, flumequine was temporarily approved for use in farmed salmonids, and during the period 1989-1994 antibacterial drug therapy in farmed salmonids acquired the character of "mono-therapy' with the quinolones flumequine and oxolinic acid. This rapid change-over in the choice of drug may partly be explained by the development of bacterial drug resistance in farmed salmonids, both to oxytetracycline and trimethoprim/sulphadiazine. The prescribing of furazolidone declined to zero during the study period. The morbidity caused by bacterial infections was defined as the number of treatment doses of antibacterial drugs per kg biomass of farmed salmonids per year. It was estimated that during the period 1988-1995, an average of 39% (mean value) of farmed salmon received, in theory, an antibacterial cure once each year. In comparison, the corresponding figure for the period 1981-1988 was 60%. However, in 1993 this figure fell to 13%, and declined even further in 1994 to 2.3%. The practice of on-farm mixing of medicated feed, using prescribed raw materials (pure drug substances) or premix formulations, declined significantly during the period 1992-1994. This was due to the introduction, in 1992, of new regulations on the prescribing of drugs to farmed fish.

Topics: Animals; Anti-Bacterial Agents; Biomass; Drug Prescriptions; Fish Diseases; Furazolidone; Longitudinal Studies; Norway; Oxytetracycline; Salmon; Trimethoprim

The effect of the antibacterial drugs flumequine (FQ) and oxytetracycline (OTC) on the defence system of the European eel (Anguilla anguilla L., 1758) was investigated using an experimentally induced infection with the parasitic swimbladder nematode Anguillicola crassus. Eight weeks after oral administration of infective larvae, the mean recovery of the parasites in FQ-treated eels was lower than in non-medicated control animals, and significantly lower than in OTC-treated eels. Mean numbers of peripheral blood granulocytes and B-lymphocytes, as well as the total number of circulating lymphoid cells, showed a significant increase as a result of the infection, while drug treatment merely affected the quantity of the lymphoid cells. The difference in protection against the parasite after FQ or OTC administration points to a modulation of the fish resistance as a result of the drug treatment. The results favour a modulation of the cellular rather than the humoral response, as no specific antibodies were found.

Topics: Air Sacs; Anguilla; Animals; Anti-Bacterial Agents; Anti-Infective Agents; Female; Fish Diseases; Fluoroquinolones; Male; Nematode Infections; Oxytetracycline; Quinolizines

A high-performance liquid chromatographic analytical method was developed for the determination of oxytetracycline in Artemia nauplii. A solid-phase extraction protocol was used to recover oxytetracycline and the internal standard tetracycline, from the Artemia samples. Oxytetracycline was analyzed using a 150 x 4.6 mm I.D. Hypersil-ODS column, a mobile phase of acetonitrile-tetrahydrofuran-0.01 M oxalic acid buffer (pH 3.0) (15:3:82, v/v), and an ultraviolet detection wavelength of 365 nm. The calibration curve of oxytetracycline in Artemia was linear (r2 = 0.9998) from 0.1 to 6.4 micrograms/g of tissue. Using a signal-to-noise ratio of 4:1 the oxytetracycline detection limit was 10 ng/g of tissue. Mean recovery of oxytetracycline amounted to 97%, while intra-assay variability was 1.5%. Quantitative data from an in-vivo feeding study indicated an excellent uptake of oxytetracycline by Artemia, as its levels reached 25.6 micrograms per g of nauplii.

Topics: Animal Feed; Animals; Artemia; Chromatography, High Pressure Liquid; Fish Diseases; Fishes; Furans; Liposomes; Oxytetracycline; Tetracycline

The in vitro antimicrobial activities of oxolinic acid, flumequine, sarafloxacin, enrofloxacin, and oxytetracycline against strains of bacteria pathogenic to fish (Aeromonas salmonicida subsp. salmonicida, atypical A. salmonicida, Vibrio salmonicida, Vibrio anguillarum, and Yersinia ruckeri) were determined at two different incubation temperatures, 4 and 15 degrees C, by a drug microdilution method. The main objective of the study was to examine the effect of incubation temperature on the in vitro activities of 4-quinolones and oxytetracycline against these bacteria. When tested against A. salmonicida subsp. salmonicida, all of the quinolones examined had MICs two- to threefold higher at 4 degrees C than at 15 degrees C. Similarly, 1.5- to 2-fold higher MICs were recorded for all of the quinolones except sarafloxacin at 4 degrees C than at 15 degrees C when the drugs were tested against V. salmonicida. In contrast to those of the quinolones, the MICs of oxytetracycline were two- to eightfold lower at 4 degrees C than at 15 degrees C against all of the bacterial species tested. Of the antimicrobial agents tested against the bacterial species included in the study, enrofloxacin was the most active and oxytetracycline was the least active. Sarafloxacin was slightly more active than flumequine and oxolinic acid, especially against oxolinic acid-resistant A. salmonicida subsp. salmonicida strains.

Topics: 4-Quinolones; Animals; Anti-Bacterial Agents; Bacteria; Fish Diseases; Fishes; Microbial Sensitivity Tests; Oxytetracycline; Temperature

Oxolinic acid, a promising drug for the treatment of bacterial fish disease agents, was tested for possible immunomodulatory effects on fish. Another antibiotic oxytetracycline, known to be immunosuppressive at higher treatment doses, and levamisole, a known immunostimulator for higher vertebrates, were also compared for causing changes in the nonspecific defense compartment and the specific immune system in rainbow trout. Groups of fish were immunized with Yersinia ruckeri O-antigen bacterin in combination with selected doses of the drugs. The nonspecific defense activity was measured by demonstrating neutrophil metabolic activity by the nitroblue tetrazolium assay, by counting engulfed bacterial cells for a phagocytic index and by counting leukocytes with adherent bacterial cells for the adherence index. The specific immune response was monitored by the passive hemolytic plaque assay demonstrating the numbers of antibody-producing cells. The results showed that oxolinic acid, used at recommended doses for the treatment of bacterial diseases, did not cause immunosuppression in either the nonspecific defense or specific immune system compartments, whereas tetracycline at 10 mg/kg caused reduced activity in both. Fish given levamisole injections before the antigen injection showed a stimulated nonspecific defense but a much reduced specific immune response.

Topics: Adjuvants, Immunologic; Animals; Antibody-Producing Cells; Antigens, Bacterial; Bacterial Adhesion; Fish Diseases; Immunization; Levamisole; Nitroblue Tetrazolium; O Antigens; Oxolinic Acid; Oxytetracycline; Phagocytosis; Salmonidae; Trout

Topics: Air Sacs; Animals; Chloramphenicol; Fish Diseases; Furazolidone; Immune Sera; Immunization; Inflammation; Methylene Blue; Neomycin; Oxytetracycline; Streptomycin; Sulfonamides

Edwardsiella tarda, an enteric, gram-negative bacterium, causes gas-filled, malodorous lesions in muscle tissue of channel catfish. Incidence and epizootiology of the disease are presented.

Topics: Administration, Oral; Animals; Diet; Disease Outbreaks; Enterobacteriaceae; Enterobacteriaceae Infections; Fish Diseases; Kidney; Oxytetracycline; Salmonidae

Topics: Administration, Oral; Amprolium; Animal Feed; Animals; Fish Diseases; Furazolidone; Oxytetracycline; Protozoan Infections; Protozoan Infections, Animal; Salmonidae; Sulfamerazine

Topics: Animals; Dog Diseases; Dogs; Fish Diseases; Fish Products; Foodborne Diseases; Oxytetracycline; Salmonidae; Species Specificity; Trematode Infections