Abstract

Listeria monocytogenes is a Gram positive facultative anaerobic microorganism that causes listeriosis in both animals and humans. The main route of infection has been identified to be by ingestion of food contaminated with the organism particularly those stored at refrigeration temperatures. This study was carried out to determine the occurrence and antimicrobial resistance profile of L. monocytogenes in salad vegetables and ready to eat vegetable salads sold in Zaria metropolis. A total of 355 samples were collected which included 250 salad vegetable samples and 105 samples of salad and coleslaw from food vending outlets within the metropolis. Confirmation of the isolates using conventional biochemical characterization showed that 14 (3.9%) of the total samples collected were positive for L. monocytogenes while 95.9% of the samples were positive for other Listeria spp. Distribution by sample type showed that 11 (4.7%) were positive for L. monocytogenes while 2 (4.4%) and 1 (1.7%) was observed in coleslaw and convention vegetable salads, respectively though the difference was not statistically significant (p value = 0.587). Cabbage and lettuce had the highest prevalence (8.5 and 6.2%, respectively) though this was not statistically significant (p value=0.517). Antibiotic susceptibility testing by disc diffusion method showed that 92.9% of the isolates were resistant to ampicillin while ciprofloxacin has the lowest resistance (14.3%). Antimicrobial resistance profile of the isolates revealed that they were all resistant to at least one antimicrobial agent. The study therefore shows that L. monocytogenes occur in salad vegetables and ready to eat salads sold in Zaria, Nigeria, therefore, adequate precaution should be taken in preparing these vegetables for both human and animal consumption. Also, the antimicrobial resistance pattern shown by the isolates is an indication that adequate measure need be taken to regulate drug use in both humans and animals in order to minimize the risk of increasing antimicrobial resistance.

Key words: Listeria monocytogenes, antimicrobial resistance, anaerobic microorganism.