Antimicrobial Resistance Profiles of Multidrug-Resistant Enterobacteria Isolated from Feces of Weaned Piglets

Nosocomial infections caused by multidrug-resistant enterobacteria have become a major challenge in global public health. Previous studies have indicated that use of antibiotics in livestock production chains is linked to the rising threat of antibiotic resistance in humans. In this study, we aimed to evaluate the distribution of genes encoding resistance to tetracycline, β-lactams, and colistin in multidrug-resistant enterobacteria isolated from feces of weaned pigs. Ninety-four enterobacteria isolates were submitted to antibiotic susceptibility test by minimum inhibitory concentration (MIC). In addition, we performed conjugation experiments to verify if plasmid-bearing isolates containing the mcr-1 gene could transfer their resistance determinant to a colistin-sensitive recipient strain. Our results demonstrated a positive association between the detection of antibiotic resistance genes in enterobacteria and the phenotypic resistance profiles of the bacterial isolates. At least one of the extended-spectrum β-lactamases (ESBL) genes (bla_CTX-M, bla_TEM, or bla _SHV) and tetA was found among most bacterial genera analyzed. In addition, results revealed that the mcr-1 gene can be transferred from E. coli UFV-627 isolate to an F^- recipient (Escherichia coli K₁₂) by conjugation. Our findings support the hypothesis that swine represents an important reservoir of antibiotic resistance genes and suggest that horizontal transfer mechanisms (e.g., conjugation) may mediate the spread of these genes in the swine gastrointestinal tract.