Antimicrobial resistance of Staphylococcus spp isolated in dairy farms and its relationship with the antimicrobial control and treatment of bovine mastitis

Abstract Antimicrobial resistance (AMR) of Staphylococcus strains from dairy farms has been attributed to the use of antibiotics in humans and animals. We conducted this research to identify the AMR genotypes and phenotypes of Staphylococcus spp isolates from different sources on dairy farms and their relationship with the control and treatment of mastitis. Antimicrobial susceptibility test was performed on 349 Staphylococcus isolates, identified by Vitek® 2 compact automated system and Maltitoff, from milk of cows with subclinical mastitis, teats of cows with and without mastitis, nasal mucosa of workers, and the environment of dairy farms. AMR genes were identified in S. aureus isolates by PCR. 152 S. aureus and 197 non-aureus staphylococci (NAS) showed resistance mainly to penicillin (54.1% and 32.4%) and ampicillin (50.3% and 27.0%), which was associated with the use of these antibiotics on farms. S. aureus isolated from workers and the environment exhibited significantly higher AMR compared to β-lactams. The identification of the blaZ (83.9%), aacA-aphD (48.6%), ermC (23.5%), tetK (12.9%) and mecA (11.8%) genes in S. aureus had low correspondence with the AMR phenotype. We conclude that the use of β-lactam antibiotics influences the expression of AMR on Staphylococcus circulating in dairy farms and that environmental and human isolates of S. aureus may be involved in the persistence of resistant strains in dairy farms.