Characterization of multidrug-resistant and ESBL-producing Gram-negative bacteria in the poultry litter-soil interface in Sergipe, Brazil.

Antimicrobial resistance (AMR) is a significant threat to global public health, frequently exacerbated by the inappropriate use of antibiotics in animal production for growth promotion, prophylaxis and therapy. This study aimed to isolate and characterize antibiotic-resistant Gram-negative bacteria from a poultry farm in Sergipe, Brazil. A total of four samples were collected, including one poultry litter sample from each poultry house (PH-1, PH-2, and PH-3) and one adjacent soil sample. Bacterial isolates were recovered using MacConkey agar supplemented with enrofloxacin (2 μg/mL). Characterization included morphological assessment, biochemical profiling (IMViC), and antimicrobial susceptibility testing by disk diffusion. Genotypic identification was performed using 16S rRNA gene sequencing, and the presence of antibiotic resistance genes (ARGs) was screened via PCR. All samples yielded enrofloxacin-resistant Gram-negative bacteria (4/4, 100%). Ten colonies with distinct phenotypic characteristics were initially selected from each sample (n = 4) to minimize the recovery of clonal isolates (n = 40). All isolates from poultry litter (n = 30) were identified as Escherichia coli. In contrast, adjacent soil samples exhibited greater taxonomic diversity, including Pseudomonas spp. (n = 4), E. coli (n = 2), Enterobacter spp. (n = 2), Atlantibacter hermannii (n = 1), and Shigella sp. (n = 1). Most isolates (n = 39) were classified as multidrug-resistant (MDR), with one isolate identified as extensively drug-resistant (XDR). Among the E. coli isolates, 27% exhibited an extended-spectrum β-lactamases (ESBL) phenotype. Molecular analysis identified several ARGs, including determinants for tetracyclines (tetA, tetB, tetG), quinolones (gyrA, qnrS), sulfonamides (sul1), and β-lactams (blaTEM, blaCTX-M-15, blaSHV). These findings highlight the significant prevalence of multidrug-resistant bacteria in poultry production environments and underscore the role of poultry litter as a reservoir for clinically relevant resistance genes. The results emphasize the urgent need for integrated surveillance and mitigation strategies within a One Health framework to limit the environmental dissemination of AMR.