Genetic diversity and antimicrobial susceptibility profiles among mastitis-causing Staphylococcus aureus isolated from bovine milk samples
- 1 July 2006
- journal article
- Published by American Veterinary Medical Association (AVMA) in American Journal of Veterinary Research
- Vol. 67 (7), 1185-1191
- https://doi.org/10.2460/ajvr.67.7.1185
Abstract
Objective—To determine whether particular antimicrobial susceptibility profiles of bovine mastitis-causing Staphylococcus aureus isolates were associated with specific S aureus genotypes. Sample Population—357 S aureus isolates recovered from milk samples submitted for diagnostic bacteriologic testing from 24 dairy herds. Procedures—Antimicrobial susceptibility of S aureus isolates was assessed by determining minimum inhibitory concentrations (MICs) to 14 antimicrobial agents. After digestion of S aureus genomic DNA by SmaI, electrophoretic patterns were obtained via pulsed-field gel electrophoresis (PFGE) and used to classify isolates into types. Gels were analyzed, and data were used to prepare dendrograms. Results—308 of 357 (86%) S aureus isolates were susceptible to all antimicrobials evaluated. Forty-nine S aureus isolates were resistant to 1 or more antimicrobials; of these isolates, 37 were resistant only to penicillin, 9 were resistant to penicillin and erythromycin, 2 were resistant to tetracycline, and 1 was resistant to erythromycin. Isolates were assigned to 7 PFGE types. An association was found between PFGE type and antimicrobial susceptibility profile. Organisms with resistance to at least one of the tested antimicrobial agents were identified in only 4 of the 7 types of S aureus. Conclusions and Clinical Relevance—Antimicrobial resistance was uncommon among the mastitis-causing S aureus isolates identified in the milk samples. A limited number of genotypes were associated with mastitis in these herds. Antimicrobial resistance phenotypes were associated with particular S aureus PFGE types; this association may have implications for future treatment and control of S aureus–associated mastitis in cattle.Keywords
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