Antimicrobial Resistant Genes in Non-Typhoidal Salmonella Species in Food and Stool Samples in Port Harcourt, Rivers State, Nigeria

Background: Non-typhoidal Salmonella (NTS) species are the major cause of foodborne infection.

Aim: To analyze antimicrobial-resistant genes found in non-typhoidal Salmonella species in food and stool samples in Port Harcourt using molecular methods.

Study Design: This was a cross-sectional study with simple randomized sampling.

Methodology: In this study, 12 Salmonella-positive isolates obtained from food and stool samples in Port Harcourt were subjected to antimicrobial sensitivity testing using the disk diffusion method of the commonly prescribed antibiotics in the city. Molecular techniques were employed to determine the presence of TET-W and CTX-M resistant genes, and also phylogenetic relationships.

Results: Out of 12 isolates [7 (3.3%) food samples and 5 (2.4%) stool samples], all (100.0%) were sensitive to ofloxacin, imipenem, levofloxacin, and gentamicin. High sensitivity was also observed to be ciprofloxacin (92.0%) and ceftriaxone (75.0%). However, complete resistance (100.0%) was recorded against tetracycline and cefotaxime. Resistance to cefpodoxime-proxetil (16.7%) and amikacin (8.3%) was exclusive to food isolates. Clinical isolates showed 20.0% resistance compared to 23.0% in food isolates, with none being sensitive to all antibiotics tested. Resistance patterns by antibiotic class indicated 0.0% resistance to fluoroquinolones, 4.2% to aminoglycosides, 25.0% to beta-lactams, and 100.0% to tetracycline. Multiple Antibiotic Resistance (MAR) analysis revealed that 75.0% of isolates had MAR indices >0.2, significantly higher (p = .0143) than those with MAR <0.2. Notably, all isolates with MAR indices >0.2 were obtained from Obio/Akpor. PCR assays confirmed the presence of resistance genes, with TET-W detected in all tested stool and food isolates, while CTX-M was found in 25.0% of food isolates but not in stool isolates.

Conclusion: There was total resistance to tetracycline antibiotics. More antimicrobial resistance was noted in food samples than in clinical samples which could have arisen from the use of antibiotics in agricultural activities or improper handling of food by vendors.