Antibiotic Resistance Profile of Salmonella sp. Isolates from Commercial Laying Hen Farms in Central-Western Brazil

Microbial resistance to antibiotics poses a significant threat to both human and animal health, necessitating international efforts to mitigate this issue. This study aimed to assess the resistance profiles of Salmonella sp. isolates and identify the presence of intl1, sul1, and blaTEM resistance genes within antigenically characterized isolates, including Agona, Livingstone, Cerro, Schwarzengrund, Salmonella enterica subsp. enterica serotype O:4.5, Anatum, Enteritidis, Johannesburg, Corvallis, and Senftenberg. These isolates underwent susceptibility testing against 14 antibiotics. The highest resistance percentages were noted for sulfamethoxazole (91%), sulfonamides (51%), and ceftiofur (28.9%), while no resistance was observed for ciprofloxacin. Salmonella Johannesburg and Salmonella Corvallis showed resistance to one antibiotic, whereas other serovars were resistant to at least two. Salmonella Schwarzengrund exhibited resistance to 13 antibiotics. The intl1 gene was detected in six out of the ten serovars, and the sul1 gene in three, always co-occurring with intl1. The blaTEM gene was not identified. Our findings highlight the risk posed by the detected multiple resistances and genes to animal, human, and environmental health. The multidrug resistance, especially to third-generation cephalosporins and fluoroquinolones, highlights the need for stringent monitoring of Salmonella in laying hens. The potential of the environment, humans, eggs, and their products to act as vectors for antibiotic resistance represents a significant concern for One Health.