Use of antimicrobial susceptibility testing of bacterial pathogens isolated from the milk of dairy cows with clinical mastitis to predict response to treatment with cephapirin and oxytetracycline.
OBJECTIVE
To determine whether results of antimicrobial susceptibility testing of bacterial pathogens isolated from the milk of dairy cows with clinical mastitis were associated with duration of clinical signs or bacteriologic cure rate following treatment with cephapirin and oxytetracycline.


METHODS
Observational study on a convenience sample.


METHODS
58 dairy cows with 121 episodes of clinical mastitis.


METHODS
Cows that only had abnormal glandular secretions were treated with cephapirin alone. Cows with an inflamed gland and abnormal glandular secretions were treated with oxytetracycline and cephapirin. Cows with systemic signs of illness, an inflamed gland, and abnormal glandular secretions were treated with oxytetracycline and flunixin meglumine and frequent stripping of the affected glands. The Kirby-Bauer method was used for antimicrobial susceptibility testing, and current guidelines were used to categorize causative bacteria as susceptible or resistant to the treatment regimen.


RESULTS
Median durations of episodes of clinical mastitis caused by susceptible (n = 97) and resistant (24) bacteria were not significantly different. Bacteriologic cure rates at 14 and 28 days were similar for episodes caused by susceptible and resistant bacteria; however, for 56 episodes of clinical mastitis caused by gram-positive bacteria and treated with cephapirin alone, bacteriologic cure rate at 28 days was significantly higher for susceptible than for resistant bacteria.


CONCLUSIONS
Results suggest that antimicrobial susceptibility testing was of no value in predicting duration of clinical signs or bacteriologic cure rate in dairy cows with mastitis, except for episodes caused by gram-positive organisms treated with intramammary administration of cephapirin alone.
Constable
Peter D
PD
Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana 61802, USA.
Morin
Dawn E
DE
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology / Q000627:therapeutic use*; D002417:Cattle; D002514:Cephapirin / Q000494:pharmacology / Q000627:therapeutic use*; D003131:Combined Modality Therapy; D024881:Drug Resistance, Bacterial; D004359:Drug Therapy, Combination; D005260:Female; D006094:Gram-Positive Bacteria / Q000187:drug effects / Q000302:isolation & purification; D007774:Lactation; D008414:Mastitis, Bovine / Q000188:drug therapy* / Q000382:microbiology; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D008892:Milk / Q000382:microbiology*; D010118:Oxytetracycline / Q000494:pharmacology / Q000627:therapeutic use*; D013997:Time Factors; D016896:Treatment Outcome
D000900:Anti-Bacterial Agents; D002514:Cephapirin; D010118:Oxytetracycline