title: Activity of selected antimicrobial agents against strains of Staphylococcus aureus isolated from bovine intramammary infections that produce beta-lactamase.
abstract: The activity of selected antimicrobial agents was determined against strains of Staphylococcus aureus that were isolated from bovine intramammary infections and that were positive or negative for beta-lactamase. A total of 107 S. aureus strains (70 that were positive for beta-lactamase and 37 that were negative for beta-lactamase) were used in the study. Production of beta-lactamase was determined using a chromogenic cephalosporin disk method. Minimum inhibitory concentrations (MIC) for each test strain were determined using a commercially available microdilution panel. The following compounds were tested: penicillin, ampicillin, oxacillin, cephapirin, ceftiofur, penicillin plus novobiocin, erythromycin, and pirlimycin. Of the five beta-lactam compounds tested, penicillin and ampicillin were most affected by beta-lactamase activity, but oxacillin, cephapirin, and ceftiofur were not affected. Penicillin plus novobiocin also demonstrated excellent activity against strains of S. aureus that were both positive and negative for beta-lactamase. Erythromycin and pirlimycin demonstrated good activity against the S. aureus strains that were negative for beta-lactamase; 90% of the isolates had an MIC of < or = 0.5 microgram/ml (MIC90). The MIC90 for erythromycin and pirlimycin for strains that were positive for beta-lactamase was > 64.0 micrograms/ml. However, 8 strains, in addition to producing beta-lactamase, were also resistant to macrolides and lincosaminides. Recalculation of the MIC90 without these 8 strains yielded equivalent values for both erythromycin and pirlimycin with strains that were positive or negative for beta-lactamase (MIC90 < or = 0.5 microgram/ml).
authors.affiliation: Animal Health Discovery Research, Pharmacia & Upjohn, Inc., Kalamazoo, MI 49001, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Watts
authors.forename: S A
authors.initials: SA
authors.lastname: Salmon
mesh_terms: D000667:Ampicillin / Q000494:pharmacology / Q000627:therapeutic use; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D002417:Cattle; D002511:Cephalosporins / Q000494:pharmacology / Q000627:therapeutic use; D002514:Cephapirin / Q000494:pharmacology / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D004352:Drug Resistance, Microbial; D004917:Erythromycin / Q000494:pharmacology / Q000627:therapeutic use; D005260:Female; D008321:Mammary Glands, Animal / Q000382:microbiology*; D008414:Mastitis, Bovine / Q000188:drug therapy / Q000201:enzymology / Q000382:microbiology*; D009675:Novobiocin / Q000494:pharmacology / Q000627:therapeutic use; D010068:Oxacillin / Q000494:pharmacology / Q000627:therapeutic use; D010406:Penicillins / Q000494:pharmacology / Q000627:therapeutic use; D013203:Staphylococcal Infections / Q000188:drug therapy / Q000382:microbiology / Q000662:veterinary*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000201:enzymology / Q000302:isolation & purification; D001618:beta-Lactamases / Q000096:biosynthesis*; D047090:beta-Lactams / Q000378:metabolism
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D010406:Penicillins; D047090:beta-Lactams; D009675:Novobiocin; D004917:Erythromycin; D000667:Ampicillin; C053503:ceftiofur; D002514:Cephapirin; D001618:beta-Lactamases; D010068:Oxacillin