Relationship between antimicrobial susceptibility of clinical mastitis pathogens and treatment outcome in cows.
OBJECTIVE
To determine whether there was any association between results of in vitro antimicrobial susceptibility testing of pathogens isolated from cows with mild or moderate clinical mastitis and outcome of treatment.


METHODS
Observational study.


METHODS
133 cows with mild or moderate mastitis in a single quarter.


METHODS
Cows were treated by means of intramammary infusion of pirlimycin (50 mg) in the affected quarter once daily for 2 days; additional intramammary treatments with the same product were administered if the milk continued to appear abnormal. Duration of treatment and days until clinical cure were recorded. Bacterial isolates were tested for antimicrobial susceptibility by means of a broth micro-dilution technique.


RESULTS
Environmental streptococci, coliforms, and coagulase-negative Staphylococcus spp were the most commonly isolated pathogens. Duration of treatment and days until clinical cure were not significantly different for cows from which pathogens that were susceptible or resistant to pirlimycin were isolated. Bacteriologic cure rates 14 and 21 days after treatment were not significantly different for cows with mastitis caused by susceptible or resistant bacteria. Similar results were found when data only from cows with mastitis caused by gram-positive isolates were analyzed.


CONCLUSIONS
In the present study, differences in clinical outcome for cows with mild or moderate mastitis that could be attributed to differences in results of in vitro susceptibility testing were not identified. The use of in vitro susceptibility testing to guide intramammary mastitis treatment cannot be recommended on the basis of results of this study.
Hoe
Fernanda G H
FG
Department of Dairy Science, University of Wisconsin, Madison, WI 53706, USA.
Ruegg
Pamela L
PL
D000818:Animals; D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D002417:Cattle; D002981:Clindamycin / Q000031:analogs & derivatives* / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial; D004755:Enterobacteriaceae / Q000187:drug effects / Q000254:growth & development; D005260:Female; D008414:Mastitis, Bovine / Q000188:drug therapy*; D008826:Microbial Sensitivity Tests / Q000662:veterinary; D008892:Milk / Q000382:microbiology*; D013210:Staphylococcus / Q000187:drug effects / Q000254:growth & development; D013291:Streptococcus / Q000187:drug effects / Q000254:growth & development; D016896:Treatment Outcome
D000900:Anti-Bacterial Agents; D002981:Clindamycin; C034093:pirlimycin