gentamicin-sulfate and Mastitis--Bovine

Bovine subclinical mastitis is an inflammation of the mammary gland caused by bacterial intramammary infection, accounting for large economic losses. Treatment of subclinical mastitis is not suggested for lactating cows due to the risk of milk contamination. The objectives of this study were to evaluate an antimicrobial peptide, nisin, in the treatment of subclinical mastitis in lactating cows. A total of 90 lactating Holstein cows with subclinical mastitis were randomly divided into nisin-treated (n = 46) and control (n = 44) groups. In the nisin-treated group, cows received an intramammary infusion of nisin at a dose of 2,500,000 IU once daily for 3 days while the control cows received no treatment. Milk samples were collected from the affected mammary quarters before treatment and 1 and 2 weeks after treatment for analyses of bacteria, somatic cells, and N-acetyl-beta-D-glucosaminidase (NAGase). Results indicated that nisin therapy had bacteriological cure rates of 90.1% for Streptococcus agalactiae (10 of 11), 50% for Staphylococcus aureus (7 of 14), 58.8% for coagulase-negative staphylococci (7 of 17), and 65.2% for all cases (30 of 46). Meanwhile, only 15.9% (7 of 44) of untreated cows spontaneously recovered. NAGase activity in milk samples and the number of mammary quarters with a milk somatic cell count of > or =500,000/ml were significantly decreased after nisin treatment while no significant changes took place in the control group. Because of its therapeutic effects on bovine subclinical mastitis, as well as its safety in humans, nisin deserves further study to clarify its effects on mastitis caused by different pathogens.

Topics: Acetylglucosaminidase; Animals; Anti-Bacterial Agents; Cattle; Cell Count; Female; Irritants; Lactation; Mammary Glands, Animal; Mastitis, Bovine; Milk; Nisin

Nocardia farcinica strains showing high-level resistance to amikacin were isolated from clinical cases in a Canada-wide bovine mastitis epizootic. Shotgun cloning of the resistance genes in the amikacin-resistant mastitis isolate N. farcinica IFM 10580 (W6220 [Centers for Disease Control and Prevention]) using a multicopy vector system revealed that the 16S rRNA gene with an A-to-G single-point mutation at position 1408 (in Escherichia coli numbering) conferred "moderate" cross-resistance to amikacin and other aminoglycosides to an originally susceptible N. farcinica strain IFM 10152. Subsequent DNA sequence analyses revealed that, in contrast to the susceptible strain, all three chromosomal 16S rRNA genes of IFM 10580, the epizootic clinical strain, contained the same A1408G point mutations. Mutant colonies showing high-level aminoglycoside resistance were obtained when the susceptible strain N. farcinica IFM 10152 was transformed with a multicopy plasmid carrying the A1408G mutant 16S rRNA gene and was cultured in the presence of aminoglycosides for 3 to 5 days. Of these transformants, at least two of the three chromosomal 16S rRNA genes contained A1408G mutations. A triple mutant was easily obtained from a strain carrying the two chromosomal A1408G mutant genes and one wild-type gene, even in the absence of the plasmid. The triple mutant showed the highest level of resistance to aminoglycosides, even in the absence of the plasmid carrying the mutant 16S rRNA gene. These results suggest that the homozygous mutations in the three 16S rRNA genes are responsible for the high-level aminoglycoside resistance found in N. farcinica isolates of the bovine mastitis epizootic.

Topics: Amikacin; Aminoglycosides; Animals; Anti-Bacterial Agents; Base Sequence; Canada; Cattle; DNA Primers; Drug Resistance, Bacterial; Female; Genes, Bacterial; Homozygote; In Vitro Techniques; Mastitis, Bovine; Microbial Sensitivity Tests; Nocardia; Nocardia Infections; Point Mutation; RNA, Bacterial; RNA, Ribosomal, 16S