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

J.I Miyebi,C.C Ezeanya,E.O Daniel

doi:10.4314/njb.v35i2.18

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 10 2 CFU/g and 83.00 x 10 2 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

Highlights

Listeria is the causative agent for “Listeriosis” an infectious disease of public health significance with vulnerable groups as immunocompromised individuals (e.g. HIV/AIDS, patients on chemotherapy), pregnant women, new-born and the elderly (Farber, 1991)
Listeria species isolated in this study include: Listeria monocytogenes (90%) and Listeria gravi (10%)
The high microbial count documented in this study provides an evidence of high level of lettuce contamination by Listeria species

Summary

Introduction

Listeria is the causative agent for “Listeriosis” an infectious disease of public health significance with vulnerable groups as immunocompromised individuals (e.g. HIV/AIDS, patients on chemotherapy), pregnant women, new-born and the elderly (Farber, 1991). Only L. monocytogenes has been associated with outbreaks of human foodborne infection (Gilbert et al, 1999) and other life-threatening illnesses ranging from severe sepsis to meningitis/encephalitis. The first documentation of Listeria in Nigeria by Eyo et al, (1969) emerged after Njoku-Obi and Njoku-Obi (1965) report using serological procedures among healthy blood donors. There emerged positive reports of Listeriosis in Nigeria. The first confirmation of Neonatal Listeriosis in Nigeria associated with L. monocytogenes was reported by Onyemelukwe and Lawande (1982) with evidence of transmission from mother to newborn. Onyemelukwe et al, (1983) and Emele (2000) reported the association of L. monocytogenes in patients with meningitis and septicaemia from Nigeria. In 2002, Shigella sonnei and Listeria monocytogenes infection were linked to lettuce consumption in diet (salad) (Pelczar et al, 2006). Even though the incidence of Listeriosis is low in Nigeria with

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Conclusion