valnemulin and Staphylococcal-Infections

The postantibiotic effect (PAE) and postantibiotic sub-minimum inhibitory concentration (MIC) effect (PA-SME) of valnemulin against Staphylococcus aureus were investigated in vitro using a spectrophotometric technique and classic viable count method. A standard curve was constructed by regression analysis of the number of colonies and the corresponding optical density (OD) at 630 nm of the inoculum. After exposure to valnemulin at different concentrations for an hour, the antibiotic was removed by centrifuging and washing. The PA-SMEs were measured after initial exposure to valnemulin at 4 × the MIC, and then, valnemulin was added to reach corresponding desired concentrations in the resuspended culture. Samples were collected hourly until the culture became turbid. The results were calculated by converting the OD values into the counts of bacteria in accordance with the curve. The MIC of valnemulin against eight strains was identically 0.125 μg ml(-1) . The mean PAEs were 2.12 h (1 × MIC) and 5.06 h (4 × MIC), and the mean PA-SMEs were 6.85 h (0.1 × MIC), 9.12 h (0.2 × MIC) and 10.8 h (0.3 × MIC). The results showed that the strains with identical MICs exhibited different PAEs and PA-SMEs. Valnemulin produced prolonged PAE and PA-SME periods for Staph. aureus, supporting a longer dosing interval while formulating a daily administration dosage.. In this study, valnemulin demonstrated prolonged postantibiotic effects and postantibiotic sub-MIC effects on strains of Staphylococcus aureus. The strains with identical MICs of valnemulin exhibited different PAEs and PA-SMEs. Staphylococcus aureus isolated from different species has little impact on the postantibiotic effect of valnemulin. The result suggests a longer dosing interval while formulating a daily administration dosage, and it may play a valuable role of valnemulin in treating Staph. aureus infections in animals.

Topics: Animals; Anti-Bacterial Agents; Bacterial Load; Chickens; Diterpenes; Microbial Sensitivity Tests; Microbial Viability; Poultry Diseases; Staphylococcal Infections; Staphylococcus aureus; Swine; Swine Diseases

The antibacterial efficacy of valnemulin against Staphylococcus aureus was studied ex vivo in broiler chickens after intravenous and intramuscular administration at a dose of 10 mg/kg bodyweight (BW). The minimum inhibitory concentrations (MICs) of valnemulin against S. aureus strains ATCC 25923 in broth and serum were 0.12 and 1 µg/mL, respectively. The MIC50 and MIC90 of valnemulin against all susceptible S. aureus strains isolated from chickens in the test population were 0.06 and 0.12 μg/mL, respectively. Protein binding, which greatly influences the efficacy of valnemulin, was assayed by equilibrium dialysate in vitro. A high binding fraction of 86.2% was found, which seems in good agreement with the difference of bacterial susceptibility tests observed in broth and serum. The surrogate index of AUC0-24/MIC required for the lowest bacteriostatic effect, and 2 log10CFU reduction in bacterial count were 24.4 h and 38.0 h, respectively. The required daily dose of valnemulin for a bacteriostatic activity was calculated to be 15 mg/kg BW based on the MIC90 of 0.12 µg/mL. Considering the slow disposition process of valnemulin and an AUC0-24 h value of more than 10-fold obtained from diseased animals, a suggested dose of 3 mg/kg BW is sufficient to achieve a satisfactory therapeutic efficacy in infected broilers. Due to the time-dependent antibacterial characteristics of valnemulin, the recommended daily dose should be split into two or three sub-doses to achieve the highest effectiveness while diminishing the risk of development of bacterial resistance.

Topics: Administration, Oral; Animals; Anti-Bacterial Agents; Area Under Curve; Chickens; Diterpenes; Injections, Intramuscular; Microbial Sensitivity Tests; Poultry Diseases; Staphylococcal Infections; Staphylococcus aureus

A novel ABC transporter gene, vga(C), was identified on the 14,365-bp multiresistance plasmid pKKS825 in a porcine methicillin (meticillin)-resistant Staphylococcus aureus isolate of sequence type 398. The vga(C) gene encodes a 523-amino-acid protein which confers resistance not only to streptogramin A antibiotics but also to lincosamides and pleuromutilins. Plasmid pKKS825 also carries the resistance genes aadD, tet(L), and dfrK, which may enable the coselection of vga(C) under selective pressure by kanamycin/neomycin, tetracyclines, and trimethoprim.

Topics: Animals; Anti-Bacterial Agents; ATP-Binding Cassette Transporters; Bacterial Proteins; Diterpenes; Drug Resistance, Multiple, Bacterial; Kanamycin; Lincosamides; Methicillin-Resistant Staphylococcus aureus; Molecular Sequence Data; Neomycin; Plasmids; Pleuromutilins; Polycyclic Compounds; Staphylococcal Infections; Streptogramin A; Swine; Swine Diseases; Tetracyclines; Trimethoprim