Characterization of virulent Listeria monocytogenes isolates recovered from ready-to-eat meat products and consumers in Cairo, Egypt

Maysa A I Awadallah,Iman I A Suelam

doi:10.14202/vetworld.2014.788-793

Abstract

Aim: This study aimed to investigate the occurrence of some virulence genes distributed in Listeria monocytogenes isolated from ready-to-eat (RTE) meat products and consumers in Cairo province, Egypt. Materials and Methods: A total of 120 beef luncheon, chicken luncheon and frankfurter beef (40 samples, each) were collected from 10 different local shops situated in Al-salam city, Cairo province, Egypt. Stool samples were collected from 40 people who had the habit of consuming RTE meat. The suspected L. monocytogenes isolates were subjected to a multiplex polymerase chain reaction (PCR) for rapid speciation and virulence determination using primers specific for inIA, inIC, and inIJ genes. Results: Culture examination of all samples on Oxford media revealed presence of colonies characteristic to L. monocytogenes in 6 beef luncheon (15%), 4 chicken luncheon (10%), 1 frankfurter beef (2.5%) and 1 human stool (2.5%) samples. Species identity of L. monocytogenes was verified through the amplification of a 800 bp fragment with inIA primers in 2 out of 6 culture isolates from beef luncheon (5%), and 1 out 4 culture isolates from chicken luncheon (2.5%) samples. Statistical analysis revealed no significant difference between the occurrence of L. monocytogenes in different food samples examined (p>0.05). The virulence of these strains was ascertained by the presence of 517 bp and 238 bp fragments of inIC and inIJ genes, respectively in the isolates that contained the 800 bp fragment. The culture isolates obtained from one frankfurter beef sample, and one human stool sample were found negative by multiplex PCR for the presence of L. monocytogenes and its virulence specific genes. Conclusion: It could be concluded that L. monocytogenes are circulating in beef and chicken luncheon sold in Cairo, Egypt. Multiplex PCR is reliable for confirmation of L. monocytogenes. This study suggests the implementation of hygienic measures at all levels from production to consumption in order to improve food safety. Furthermore, authors recommended consumption of beef frankfurter or any RTE meat sold in their original intact packing due to low level of contamination.

Highlights

Listeriosis has been recognized as an emerging food borne zoonoses [1]
Statistical analysis revealed no significant difference between the occurrence of L. monocytogenes in different food samples examined (p>0.05)
The culture isolates obtained from one frankfurter beef sample, and one human stool sample were found negative by multiplex polymerase chain reaction (PCR) for the presence of L. monocytogenes and its virulence specific genes

Summary

Introduction

Listeria monocytogenes has been recognized as an important opportunistic human pathogen since 1929 and as food borne pathogen since 1981 [2]. Ready-to-eat (RTE) meat products are, usually, cooked during manufacture and consumed without further heating. They present high risk to the consumers due to possible cross contamination with food borne pathogens and further growth of such pathogens [3]. The extended distribution throughout the food processing environment and asymptomatic human carriers [4] and the psychrotrophic character of Listeria species appear to be the main causes of the prevalence in different kinds of refrigerated RTE meat products and contamination could occur either pre- or post-processing [5].

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