Resistance to third-generation cephalosporins and quinolones in Escherichia coli isolated from broiler chicken feces and carcasses at slaughter in Rio de Janeiro state, Brazil

Costa, Gisllany AlvesDias, Thomas SallesFialho, Daniele SoaresSilva, Larissa de Assis MonteiroFigueira, Arthur de AlmeidaCunha, Nathalie Costa daPereira, Virginia Léo de AlmeidaAbreu, Dayse Lima da Costa

ABSTRACT: Escherichia coli is a significant component of the poultry intestinal microbiota and a critical indicator of antimicrobial resistance. This study investigated the antimicrobial susceptibility and the presence of cephalosporin and quinolone resistance genes in E. coli strains isolated from broiler chicken feces and carcasses in Rio de Janeiro, Brazil. Phenotypic resistance characterization was performed using Disk Diffusion and Double Disk Synergy Tests (DDST) for cephalosporin and quinolone antimicrobials, while resistance genes were detected by PCR. Statistical analyses were conducted using Chi-square and Fisher's Exact tests. Results indicated that 44.4% of the strains were resistant to at least one cephalosporin, with a higher resistance frequency observed in carcass isolates. Furthermore, 61.4% of strains were identified as Extended-spectrum β-lactamases (ESBL) producers through DDST, also with a higher prevalence in carcass samples. Resistance to at least one quinolone was detected in 96% of the strains, with no significant difference between feces and carcass isolates, except for nalidixic acid, which showed higher resistance in fecal isolates. The bla TEM gene was most frequently detected in both sources, followed by bla CTX-M, which was more prevalent in carcasses. CTX-M groups 1, 2, 8, and 9 were identified, with CTX-M-2 being the most frequent. Among quinolones, qnrA, qnrB, qnrD, and qnrS genes were detected, with qnrB predominating. The bla SHV, bla CTX-M-25, and qnrC genes were not found. This study highlighted the detection of ESBL or genes encoding this characteristic and the high prevalence of quinolone-resistant E. coli carrying various qnr genes in poultry farms in Rio de Janeiro, Brazil.