Antibiotic Resistance Genes in Cattle Gut Microbiota: Influence of Housing Conditions

Resistance to antimicrobial drugs is an urgent problem not only in public health, but also in animal husbandry. The widespread use of antimicrobials in feed additives is one of the main reasons for the rapid spread of antibiotic resistance in the microbiota of the gastrointestinal tract of farm animals. To characterize antibiotic resistance genes (resistome), we performed metagenomic analysis of the feces of 24 cattle from different regions of Russia, including cows of different breeds and yaks. Animals differed in the type of housing: year-round on pastures or in barns of conventional farms, with consumption of feed additives. Although genes of resistance to aminoglycosides, β-lactams, glycopeptides, MLS antibiotics (macrolides, lincosamides, and streptogramins), phenicols, and tetracyclines were detected in samples from both groups of animals, the content of the resistome in the fecal microbiome of stall-bred cattle was about ten times higher than in animals kept on pastures. The resistome of stall cattle was dominated by β-lactamases and tetracycline resistance genes, the content of which in the microbiome was 24 and 60 times higher, respectively, than in animals kept on pastures. Apparently, the spread of resistance to β-lactams and tetracyclines in stall cattle reflects the active use of these antibiotics in livestock production. Metagenomic analysis of livestock feces can be used to quantify antibiotic resistance genes for the purpose of monitoring antimicrobial drugs used in animal husbandry.