Listeria species as contaminants of lettuce and its resistant genes in Benin city, Nigeria

Abstract

This study was aimed at determining the level of Listeria contaminants and subsequently detects some resistance genes among the isolated Listeria species from lettuce sold in some vegetable markets in Benin City, Nigeria. Twenty-four lettuce samples were purchased from three vegetable markets in Benin City, Nigeria and examined using standard microbiological methods. Microbial characterization revealed Listeria monocytogenes and L. grayi as the predominant species isolated. Plate count analysis on Listeria selective agar revealed that lettuce sold in Oba market and Forestry market had the highest and lowest mean count of Listeria species 224.00 x 10² CFU/g and 83.00 x 10² CFU/g respectively. Most (63.75%) of the Listeria species isolates were found to be susceptible to Ofloxacin (5 μg), Ciprofloxacin (10 μg), Streptomycin (10 μg), Gentamycin (10 μg), Pefloxacin (5 μg) whereas species harbouring tetracycline (65%) and erythromycin (60%) resistant genes. The study provides an evidence of the colonization of Listeria species in lettuce sold in Benin City which may pose serious public health threat to the populace.

Keywords: Listeria monocytogenes, Listeria grayi, Lettuce, Resistance genes