Isolation and Identification of Listeria monocytogenes in Fresh Croaker (Pseudotolithus senegalensis)

Abstract

Listeria monocytogenes is an important foodborne pathogen. Food products contaminated with this bacterium causes listeriosis which is a disease with high mortality and hospitalization rate. It is a known threat to food safety due to its persistence in food processing environment and its ability to survive and grow at several environmental conditions. In this study, a total of 108 fresh croaker samples were collected from retail outlets in Lagos, Nigeria. The isolation of L. monocytogenes involved the use of culture methods based on selective enrichment and plating. Isolates were identified by colony morphology, sugar fermentation and haemolytic properties. Genotypic identification of L. monocytogenes was performed using PCR incorporating 16S rRNA followed by DNA sequence analysis. Eight samples (7.4%) were positive for L. monocytogenes. The sequence and phylogenetic analysis based on the 16S rRNA showed that fresh croaker L. monocytogenes isolates were grouped into two different clusters when compared with reference L. monocytogenes indicating that they belong to different ancestors. This study revealed the presence of L. monocytogenes in fresh croaker in low concentration. However, vulnerable populations are still at risk if these products are consumed raw or lightly cooked.