Minimum inhibitory concentrations of selected antimicrobials against Escherichia coli and Trueperella pyogenes of bovine uterine origin.
Minimum inhibitory concentrations (MIC) of 9 antimicrobials for isolates of 2 common bovine intrauterine bacterial pathogens, Escherichia coli (n=209) and Trueperella pyogenes (n=35), were determined using broth microdilution methodology. The isolates were recovered from dairy cows from 7 herds postpartum using the cytobrush technique. The pathogens were initially identified using phenotypic techniques. Additionally, PCR was used to confirm the identity of T. pyogenes isolates and to categorize the E. coli isolates into phylogenetic groups A, B1, B2, and D. Minimum inhibitory concentrations in excess of published cut-points or bimodal distributions of MIC indicated potential antimicrobial resistance to ampicillin, cefuroxime, cephapirin, and oxytetracycline for E. coli, and to oxytetracycline for T. pyogenes. Of the antimicrobials tested, ticarcillin/clavulanic acid, ceftiofur, and enrofloxacin had the lowest MIC for these 2 pathogens. Differences in MIC of some antimicrobials were found between herds, age, breeds, and E. coli phylogenetic groups. Isolation of E. coli with an MIC ≥8μg/mL of oxytetracycline at 23d postpartum was associated with a lower probability of pregnancy within 6wk of commencement of breeding compared with those isolates with an MIC <8μg/mL (relative risk=0.66). Minimum inhibitory concentrations for uterine pathogens were determined for isolates from New Zealand dairy cows. However, in the absence of either epidemiological or clinical interpretive criteria, the interpretation of these MIC remains unclear. Further studies are required to define interpretative criteria, including determination of pharmacokinetic and pharmacodynamic profiles for antimicrobials.
Cognosco, Anexa Animal Health, Morrinsville 3300, New Zealand; Epicentre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North 4442, New Zealand. Electronic address: mdeboer@anexa.co.nz.
Melvin
M
de Boer
Epicentre, Institute of Veterinary, Animal and Biomedical Sciences, Massey University, Palmerston North 4442, New Zealand.
Cord
C
Heuer
Pokeno 2471, New Zealand.
Hassan
H
Hussein
Cognosco, Anexa Animal Health, Morrinsville 3300, New Zealand.
Scott
S
McDougall
D000191:Actinomycetaceae / Q000187:drug effects*; D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage / Q000494:pharmacology*; D002417:Cattle; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D005260:Female; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D009520:New Zealand; D010802:Phylogeny; D011247:Pregnancy
D000900:Anti-Bacterial Agents
antimicrobial susceptibility; dairy cow; minimum inhibitory concentration; uterine infection