Antimicrobial Susceptibility and Molecular Characterization of Tetracycline Resistance Genes in <i>Listeria monocytogenes </i>Isolated from Live Chickens in Jos, Nigeria

Abstract

Listeria monocytogenes remains a critical foodborne pathogen, particularly in poultry production systems where microbial persistence and antimicrobial resistance are prevalent. This study determined the antimicrobial susceptibility and characterized tetracycline resistance genes in Listeria monocytogenes isolated from live chickens in Jos, Nigeria. A total of 40 swab samples (cloacal, beak, and feet) were analyzed using standard cultural, biochemical, and PCR-based methods. The organism was detected in 15.0% of samples, with feet swabs accounting for the highest recovery (10.0%). Bacterial loads ranged from 4.0 × 10² to 1.1 × 10³ CFU/g; statistical analysis showed no significant relationship between the counts and the part of the chicken where samples were collected (p=0.35). Antimicrobial susceptibility testing revealed extensive multidrug resistance, including complete resistance to amoxicillin, gentamicin, and meropenem, and high resistance to ampicillin and tetracycline. Multiple Antibiotic Resistance (MAR) indices (0.38–1.00) reflected strong selective pressure from antimicrobial exposure. PCR amplification confirmed the isolates via 16S rRNA and hly genes, while molecular screening demonstrated universal carriage of the tet(A) gene, with tet(M) absent suggesting efflux-mediated tetracycline resistance predominates in this population. The detection of pathogenic, multidrug-resistant Listeria monocytogenes in live chickens underscores a significant public health risk and highlights the urgent need for improved biosecurity, regulated antimicrobial use, and strengthened surveillance within poultry production systems.