Detection and Determination of the Frequency of Listeria monocytogenes in Food samples by Molecular analysis of the hlyA gene

Listeriolysin (LLO) is a sulfhydryl-activated hemolysin bound to cholesterol, that is encoded by the hlyA gene of Listeria monocytogenes. The aim of this study was to detect and determine the frequency of Listeria monocytogenes in food samples through molecular analysis of the hlyA gene.

The present study was a descriptive cross-sectional assay conducted from the middle of October 2018 to the end of January of the same year. One hundred sixty-five samples of different types of meat, vegetables, hamburgers and shrimps were examined. Samples were randomly collected from restaurants, delicatessens, prepared food places, and different supermarkets. All samples were analyzed with phenotypic and biochemical tests. The samples suspected of Listeria monocytogenes, after DNA extraction, were evaluated by PCR with specific primers for the hlyA gene. Then the data and results were evaluated with using SPSS v.23 software and Excel software.

Phenotypic methods (microbial culture and biochemical investigation) confirmed 18 positive samples for Listeria monocytogenes, of which 10 (6.06%) samples were positive for Listeria monocytogenes by PCR of the hlyA gene. The rate of contamination in pounded kebab was 37.9%, chicken meat 4.4%, local hamburger 16.66% and lettuce 13.33%. Compared to other studies, these findings were more prevalent in some foods (e.g., local hamburger) and less in others (e.g., chicken meat).

The use of biochemical methods for determining the frequency of Listeria monocytogenes in food samples in Sanandaj had a high percentage of false positives.