Methicillin-resistant Staphylococcus (MRS) present in the udder ofdairy cows with clinical and subclinical mastitis on a commercial farm in Jataí-GO, Brazil: scientific article
DOI:
https://doi.org/10.11606/issn.1678-4456.bjvras.2025.236172Keywords:
MRS, Antibiogram, Phenotypic expression, Dairy cattleAbstract
Among the primary diseases affecting the Brazilian dairy herd is bovine mastitis, a complex, multifactorial disease whose primary pathogen is Staphylococcus spp., which is known for its high resistance to beta-lactam antimicrobials and environmental factors. The present study aimed to isolate staphylococci from milk samples collected from cows at a dairy farm in Jataí, GO, Brazil. Isolation was carried out using samples from 90 sick animals collected between November and March. After isolation and identification, antibiotic tests were performed to assess resistance and investigate the presence of associated virulence genes. The method chosen for the antibiogram was disk diffusion, which we used to evaluate two groups of animals with clinical and subclinical mastitis at that property. Of the milk samples analyzed, 58.9% were positive for Staphylococcus sp., with 5.5% coagulase-positive (SPC) and 53.3% coagulase-negative (SCN). The SPC bacteria were associated with clinical and subclinical mastitis, while SCN was often associated with subclinical mastitis (68.75%). The high frequency of Staphylococcus sp. indicates they remain a primary causative agent of mastitis, with SCN having the greatest impact in this herd. Among the antibiotics tested, we found three with prevalent resistance, namely, oxacillin, penicillin, and vancomycin. We also identified coagulase-negative staphylococci (CoNS) as the predominant cause of subclinical mastitis in the bovine herd. Methicillin-resistant (MRS) and vancomycin resistant Staphylococcus isolates stood out as causes of mastitis. MRS isolates also underwent a polymerase chain reaction (PCR) test to detect the mecA and mecC genes. However, no isolate exhibited those resistance genes. This shows that antibiotic resistance may occur through other mechanisms and genes.
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