Antimicrobial resistance of bacteria isolated from dairy cow milk samples submitted for bacterial culture: 8,905 samples (1994–2001)

Abstract
Objective—To determine whether antimicrobial resistance patterns of major mastitis pathogens isolated from milk samples from dairy cows have changed over time.Design—Retrospective study.Sample Population—8,905 bacterial isolates obtained from milk samples submitted to the Wisconsin Veterinary Diagnostic Laboratory between January 1994 and June 2001.Procedure—Antimicrobial susceptibility was determined by means of the Kirby-Bauer disk diffusion method. Logistic regression was used to determine whether percentages of isolates resistant to various antimicrobials changed over time.Results—For the gram-positive mastitis pathogens, percentages of isolates resistant to various β-lactam antimicrobials did not increase over the course of the study. Percentage ofStaphylococcus aureusisolates resistant to penicillin decreased from 49 to 30%; percentage ofStreptococcusisolates resistant to penicillin decreased from 6 to 1%. Percentage of isolates resistant to erythromycin increased forS aureus,Escherichia coli, Enterobacterspp,Enterococcusspp, andPasteurellaspp. Percentage of isolates resistant to lincomycin increased forS aureusandStaphylococcusspp. Percentage of coagulase-negativeStaphylococcusisolates resistant to pirlimycin increased from 6 to 19%. For several pathogens, percentages of isolates resistant to sulfisoxazole and to trimethoprim-sulfamethoxazole decreased. No pathogens had a significant increase in the percentage of isolates resistant to novobiocin-penicillin.Conclusions and Clinical Relevance—Results did not indicate a trend toward increased antimicrobial resistance among mastitis pathogens isolated from milk samples from dairy cows between 1994 and 2001. Reduced resistance to β-lactam antimicrobials was identified for several gram-positive mastitis pathogens. (J Am Vet Med Assoc2003;222:1582–1589)

This publication has 13 references indexed in Scilit: