Fecal cultivable aerobic microbiota of dairy cows and calves acting as reservoir of clinically relevant antimicrobial resistance genes.

Antimicrobial resistance has become a global threat to public health since multidrug-resistant (MDR) bacteria have been reported worldwide carrying different antimicrobial resistance genes (ARGs), and animals have been described as a reservoir of ARGs. The presence of antimicrobial-resistant bacteria and ARGs in the food matrix is a risk to public health. This study aimed to research the presence of clinically relevant ARGs for important antimicrobials and genetic elements in fecal samples from dairy cows and calves on a Brazilian farm. In this study, a total of 21 fecal samples were collected, and then, the DNA of cultivable aerobic bacteria was extracted. Fifty-seven ARGs and twenty-three genetic elements were researched by PCR and confirmed by sequencing. Several ARGs that confer resistance to β-lactams, tetracyclines, fluoroquinolones, sulphonamides, phenicols, aminoglycoside, glycopeptides, and macrolides were detected. A total of 200 amplicons from 23 ARGs (bla, bla, bla, tetA, tetB, tetC, qepA, qnrB, qnrS, oqxA, oqxB, vanC1, vanC2/3, aadA, sul1, sul2, sul3, ermB, mefAE, floR, cmlA, aadA, aph(3')-Ia, aac(3')-Ia), and 145 amplicons from 12 genetic elements (IncF, IncFIA, IncFIB, IncI1, IncY, IncU, IncK, IncP, IncR, IncHI1, ColE-like, intI1) were detected. The results presented in this study call attention to the monitoring of antimicrobial resistance in dairy farms worldwide. MDR bacteria and ARGs can spread to different sources, including milk products, which are one of the most consumed products worldwide, representing a potential risk to human health.