ANTIBIOTIC RESISTANCE IN LISTERIA ISOLATES FROM FRESH VEGETABLES IN LAGOS STATE, NIGERIA

Listeria species are important foodborne pathogens that have increasingly been associated with fresh produce due to contamination during cultivation, harvesting, transportation, and marketing. The emergence of antibiotic-resistant Listeria strains in foods poses a significant public health concern because such organisms may transfer resistance determinants through the food chain. This study investigated the antibiotic resistance profiles of Listeria isolates recovered from fresh vegetables sold in selected markets in Lagos State, Nigeria. A total of 354 vegetable samples comprising lettuce, cabbage, and carrot were collected from five major markets. Isolation was performed using PALCAM agar, while identification was achieved using Analytical Profile Index (API) kits. Antibiotic susceptibility testing was conducted using the disk diffusion method. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were determined using the microbroth dilution technique. The isolates were identified as Listeria monocytogenes, Listeria innocua, and Listeria ivanovii, with L. monocytogenes being the predominant species. High resistance rates were observed against rifampicin, perfloxacin, erythromycin, sulphamethoxazole-trimethoprim, oxacillin, and chloramphenicol, whereas susceptibility was generally observed for tigecycline, gentamicin, amoxicillin, and vancomycin. Multiple antibiotic resistance index values ranged from 0.31 to 0.62. MIC and MBC analyses revealed varying resistance levels among isolates, with Listeria monocytogenes exhibiting the highest resistance patterns. The findings demonstrated the occurrence of multidrug-resistant Listeria species in fresh vegetables sold in Lagos markets, highlighting the need for improved food safety practices and antimicrobial resistance surveillance.