Antimicrobial Resistance Profiles of Isolated from Cows with Subclinical Mastitis: Do Strains from the Environment and from Humans Contribute to the Dissemination of Resistance Among Bacteria on Dairy Farms in Colombia?
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is a very prevalent etiologic agent of bovine mastitis, and antibiotic resistance contributes to the successful colonization and dissemination of these bacteria in different environments and hosts on dairy farms. This study aimed to identify the antimicrobial resistance (AMR) genotypes and phenotypes of spp. isolates from different sources on dairy farms and their relationship with the use of antibiotics. An antimicrobial susceptibility test was performed on 349 strains (, = 152; non-aureus staphylococci (NAS), = 197) isolated from quarter milk samples (QMSs) from cows with subclinical mastitis (176), the teats of cows (116), the milking parlor environment (32), and the nasal cavities of milk workers (25). Resistance and multidrug resistance percentages found for and NAS were ( = 63.2%, NAS = 55.8%) and ( = 4.6%, NAS = 11.7%), respectively. and NAS isolates showed resistance mainly to penicillin (10 IU) (54.1% and 32.4%) and ampicillin (10 mg) (50.3% and 27.0%) drugs. The prevalence of AMR was higher in environmental samples (81.3%) compared to other sources (52.6-76.0%). In isolates, the identification of the (83.9%), (48.6%), (23.5%), (12.9%), and (12.1%) genes did not entirely agree with the AMR phenotype. We conclude that the use of β-lactam antibiotics influences the expression of AMR in circulating on dairy farms and that isolates from the environment and humans may be reservoirs of AMR for other bacteria on dairy farms.
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