The Landscape of Salmonella enterica Serovar Gallinarum-Pullorum Antimicrobial Resistance in Bangladesh's Poultry Industry: A Combined Phenotypic and Molecular Study.

Salmonella enterica serovar Gallinarum-Pullorum is a prevalent poultry-borne pathogen that could facilitate the zoonotic transmission of multidrug-resistant (MDR) strains to humans, significantly contributing to the global burden of antimicrobial resistance (AMR). A total of 200 samples were collected from chickens of various flocks suspected of salmonellosis based on clinical diagnosis and isolation via standard bacteriological protocols, of which 138 tested positive for serovar Gallinarum-Pullorum by polymerase chain reaction (PCR). Each PCR-positive sample's isolates were sent for antimicrobial susceptibility testing, and each PCR-positive sample's DNA samples were sent for PCR-based resistance gene detection to evaluate the effectiveness of antimicrobials, MDR, and AMR status. Isolates were sensitive to gentamicin, amoxicillin-clavulanic acid, and cephalexin at rates of 84.78%, 83.33%, and 81.78%, respectively. Conversely, amoxicillin (71.01% resistant) and tetracycline (73.91% resistant) showed the highest rates of resistance. The MDR group accounted for 123 isolates, translating to a commanding combined prevalence of 89.13%, and resistance peaked at four resistant agents, with an incidence of 31.16% (43). Multiple antibiotic resistance (MAR) Index levels varied from 0.1 to 0.7. AML-SXT-TE-NOR and AML-SXT-TE-NOR-ENR were the most commonly seen patterns, each occurring in five isolates (3.62%). The tetA (74.64%) and the sul1 (73.19%) were the most prevalent resistance genes, with the presence of blaCMY (71.01%), blaTEM (9.42%), blaCTX (7.97%), sul2 (55.80%), dfrA1 (37.68%), aph(3')-IIa (42.03%), aac(3)-VIa (5.80%), aadB (3.62%), floR (35.51%), gyrA (60.87%), and parC (47.83%) genes. This study reveals that S. enterica exhibits high levels of AMR, manifesting in MDR phenotypes supported by a robust presence of resistance-conferring genes.