International Journal of Sub-Saharan African Research (IJSSAR)

Background: In Nigeria, vegetables are often prone to contamination that leads to food-borne disease with significant public health and economic burdens such as listeriosis. Persistence of such contamination could be due to inadequate hygienic practices and poor handling which affect food safety, quality, and security. Limited empirical data on antimicrobial resistance patterns and virulence gene profiles of Listeria species in vegetables create gap in evidence needed for effective surveillance and control strategies.
Objective: This study assessed detection and prevalence of antimicrobial resistance patterns, and virulence gene profiles of Listeria monocytogenes with other Listeria species in vegetables obtained from selected Nigerian markets. Methods: A cross-sectional study was conducted on 270 vegetable samples comprising cucumber (n = 90), cabbage (n = 90), and carrot (n = 90), obtained from 30 markets across selected Nigerian states. Samples were collected directly from farmers’ vendors, and analyzed for presence of Listeria species using standard microbiological and molecular techniques. Antimicrobial susceptibility testing was performed against 15 antibiotics using the disk diffusion method. Polymerase chain reaction (PCR) assays were used to detect 18 antimicrobial resistance genes and 9 virulence-associated genes in the isolates. Results: Antimicrobial resistance genes were identified across Listeria species. Listeria monocytogenes showed resistance to chloramphenicol, aminoglycosides, and vancomycin; L. ivanovii to carbapenems; L. seeligeri to chloramphenicol, aminoglycosides, tetracycline, and vancomycin; L. innocua to macrolides, vancomycin, and fluoroquinolones; and L. grayi to macrolides, vancomycin, aminoglycosides, and chloramphenicol. Virulence genes (prs, hlyA, clpE, plcA, prfA, iniB, actA, RADP) were detected in L. monocytogenes from cabbage samples in Agege (77.78%) and Oshodi (44.44%) markets, except plcB. L. grayi exhibited all assessed virulence genes in cabbage and carrot samples. Conclusions: This study concludes that there was presence of six strains of Listeria spp (including Listeria monocytogenes) in the vegetable with antimicrobial resistance and virulent genes, which might be due to consequences of cross-contamination, along farm-market supply chain. Handlers must thereby ensure good production, hygienic handling, and practices from farm to plate. Unique contributions: This study provides novel insights into detection and prevalence of antimicrobial resistance, and virulence profiles of Listeria monocytogenes and other Listeria species in fresh vegetables across Nigerian markets. It highlights the presence of hypervirulent and multidrug-resistant strains in commonly consumed vegetables, demonstrating environmental contamination in Osun State and high virulence potential in Ondo State. These findings offer critical evidence for understanding microbial safety of vegetables in Nigeria and emphasized on the need for targeted surveillance and improved handling practices along farm-to-market supply chain.
Key Recommendation: To mitigate the risk of listeriosis from fresh vegetables, it is recommended that hygienic handling practices and proper storage be enforced along the farm-to-market supply chain. Regular surveillance and monitoring of Listeria contamination, coupled with adherence to food safety standards, are essential to reduce the prevalence of multidrug-resistant and virulent strains in commonly consumed vegetables.