Resumo

Staphylococcus aureus infections are a concern in human and animal health. This pathogen has been found in different human environments (community and hospitals) and animal species. Strains resistant to methicillin (MRSA) have been found, and its detection is important once they usually have multidrug resistance. Moreover, a reduced number of clones have been successfully colonizing or causing disease in specific hosts. Molecular typing by MLST (Multi Locus Sequence Typing) and spa typing have been used to study the epidemiology of S. aureus colonization and infection. The aim of this study was to type S. aureus isolated from bulk tank milk of 33 dairy herds by MLST and spa typing, evaluating their epidemiology in São Paulo State. One hundred microliters of milk and its dilutions in saline were cultured on Baird Parker agar. Up to 10 typical and atypical S. aureus colonies were subcultured on blood agar. S. aureus identification was confirmed by phenotypic (coagulase and fermentation of sugars) and genotypic (PCR) methods. One isolate from each farm was used to determine genotypic methicillin resistance, and to perform MLST and spa typing. All isolates were methicillin-susceptible. We identified 14 sequence types (STs), including 6 novel types (ST2510, ST2517, ST2518, ST2519, ST2520, and ST2521), distributed in 7 clonal complexes: CC1 (36.4%), CC97 (21.2%), CC126 (18.2%), CC5 (12.1%), CC30 (6.1%), CC8 (3%) and CC133 (3%). Fourteen spa types were identified, including one novel type (t11364). CCs of MSSA already reported in studies on bovine mastitis in other countries and Brazil (Rio de Janeiro State) were found, demonstrating the presence of these CCs in bulk tank milk from São Paulo. Additionally, novel STs and a spa type were found. The majority of the isolates belonged to CC97, showing the diversity of these bovine isolates in Brazil. Some farms situated close to each other shared identical S. aureus strains by MLST, and their CCs (CC1, CC5, CC30, CC97, and CC126) were previously found in the Southeast region of Brazil, suggesting that they might be usual in this region. Moreover, there was similarity observed between spa types that belong to the same CC - in CC97 and CC1 (highlighting t177). These findings of high homology of repeats belonging to the same MLST CC and between different CCs show that spa typing can be used with MLST as additional tool to determine genetic relationship. FAPESP Post-Doc fellowship 2010/17222-8 and International Internship scholarship 2012/05967-4 FAPESP Grant 2011/09106-0