Antimicrobial resistance and genotypic relatedness of environmental staphylococci in semi-extensive dairy farms

This study aimed to investigate the occurrence, genotypic relatedness and antimicrobial resistance of Staphylococcus aureus and coagulase-negative Staphylococcus from milk and environmental sources in dairy herds. A total of 110 staphylococci recovered from 147 samples collected at 21 semi-extensive dairy farms in Northeastern Brazil were investigated. Staphylococcus aureus isolates were identified and screened for methicillin resistance by means of a duplex-PCR. The highest frequency of contamination by S. aureus was observed for milk samples (38.1%), while contamination by coagulase-negative staphylococci (CoNS) was most commonly detected in milkers’ hand swabs (52.4%) and environmental samples (29.5%). Two mecA-positive Staphylococcus aureus (2/40; 5%) were detected, while the same gene was found in fourteen (14/70; 20%) CoNS. Clonally related isolates from milk and environmental sources, such as the surface of gates, were detected by PFGE. This study reports the occurrence of MRSA in dairy farms under semi-extensive production practices and reinforces the importance of environment as a source of Staphylococcus contamination in dairy herds.