Pulsed-field gel electrophoresis genotyping and antimicrobial resistance profiles of Staphylococcus aureus isolated from subclinical mastitis in dairy cattle in Brazil

Staphylococcus aureus is a contagious pathogen frequently associated with bovine subclinical mastitis (SCM) cases in Brazil. Molecular characterization of S. aureus allows monitoring of specific features at the strain level, such as transmission routes and antimicrobial resistance, and it can be a helpful tool for implementation of prevention measures among and within herds. We evaluated molecular typing and antimicrobial resistance profiles of S. aureus isolates from lactating cows with SCM. A total of 79 S. aureus isolates recovered from bovine SCM were submitted to pulsed-field gel electrophoresis (PFGE) analysis and tested for antimicrobial susceptibility against 13 antimicrobials, based on minimum inhibitory concentrations. Based on the band patterns generated by PFGE, dendrograms were constructed to compare S. aureus pulsotypes (n = 17). Resistance was observed for amoxicillin (100% of the isolates), erythromycin (96%) and for ampicillin and penicillin (77%). All S. aureus isolates were susceptible to gentamicin, enrofloxacin, ciprofloxacin and tetracycline. One methicillin-resistant S. aureus strain was identified based on resistance to cefoxitin. We found a wide genotypic diversity of S. aureus causing SCM among the isolates. In general, S. aureus was sensitive to quinolones and aminoglycosides, while we observed β-lactams resistance in most of the isolates. Our findings are similar to those of previous results that reported high resistance of S. aureus mainly to β-lactams. Consequently, control measures for this bacterium need to be implemented in order to control the spread of the disease and establish more assertive treatment protocols.