The Activity of a Combination of Penicillin and Novobiocin Against Bovine Mastitis Pathogens: Development of a Disk Diffusion Test

• Published in: Journal of dairy science 1997-02, Vol.80 (2), p.413-421
• Main Authors: Thornsberry, C., Burton, P.J., Yee, Y.C., Watts, J.L., Yancey, R.J.
• Format: Article
• Language: English
• Subjects: Animal productions; Animals; Anti-Bacterial Agents - administration & dosage; Anti-Bacterial Agents - pharmacology; ANTIBACTERIAL PROPERTIES; ANTIBIOTICOS; ANTIBIOTICS; ANTIBIOTIQUE; ANTIMICROBIAL PROPERTIES; antimicrobial susceptibility tests; ASSOCIATION MEDICAMENTEUSE; Biological and medical sciences; BOVINE MASTITIS; Cattle; Diffusion; DOSAGE; DOSIFICACION; DRUG COMBINATIONS; Drug Therapy, Combination; DRUGS; EFFICACY; FARMACOLOGIA; Female; Fundamental and applied biological sciences. Psychology; LAIT; LECHE; MAMMITE BOVINE; MASTITIS BOVINA; Mastitis, Bovine - drug therapy; Mastitis, Bovine - microbiology; MEDICAMENT; MEDICAMENTOS; MEZCLA DE MEDICAMENTOS; Microbial Sensitivity Tests; MILK; minimum inhibitory concentration; Novobiocin - administration & dosage; Novobiocin - pharmacology; PENICILINA; PENICILLINE; PENICILLINS; Penicillins - administration & dosage; Penicillins - pharmacology; PHARMACOLOGIE; PHARMACOLOGY; PROPIEDADES ANTIMICROBIANAS; PROPRIETE ANTIMICROBIENNE; RESIDU; RESIDUES; RESIDUOS; SINERGISMO; Staphylococcus - drug effects; STAPHYLOCOCCUS AUREUS; STREPTOCOCCUS; Streptococcus - drug effects; SYNERGISM; SYNERGISME; Terrestrial animal productions; Vertebrates
• ISSN: 0022-0302; 1525-3198
• DOI: 10.3168/jds.S0022-0302(97)75952-6

The combination of penicillin and novobiocin is currently available for the treatment of bovine mastitis, but methods are not available for susceptibility testing of the combination by veterinary diagnostic laboratories. The minimum inhibitory concentration (MIC) and disk diffusion data were determined for penicillin, novobiocin, and a combination of the two in a 1:2 ratio for 225 staphylococcal, streptococcal, and Gram-negative isolates from bovine intramammary infections. Based on the drug concentrations in milk following infusion, linear regression analysis, and error rate bounding, the interpretive zone diameters selected were ≤16mm for resistant isolates and≥17mm for susceptible isolates with a disk containing 10U of penicillin and 30μg of novobiocin. Additionally, MIC breakpoints of ≤2μg/ml of penicillin and 4μg/ml of novobiocin were selected to categorize isolates as susceptible and≥4μg/ml of penicillin and 8μg/ml of novobiocin were selected to categorize isolates as resistant. The MIC and disk diffusion results, as well as studies to monitor bacterial killing by antimicrobial agents over time, indicated that the combination of penicillin and novobiocin in a 1:2 ratio was more active than were the individual drugs. Kinetics of the kill curves with the penicillin and novobiocin combination (1:2 ratio) showed that the combination was bactericidal for Staphylococcus aureus and Staphylococcus xylosus.