The investigation of molecular characterization of presumptive Listeria monocytogenes isolates from a food-processing environment

Listeria is a Gram-positive, non-spore forming, facultative anaerobic intracellular bacterium. The most important pathogens in mammals include Listeria monocytogenes and Listeria ivanovii. The former generally causes disease and death in both humans and animals while the latter performs sporadically and primarily causes illness in ruminants. The aim of this project was to use conventional and molecular techniques to determine whether the provided samples were L. monocytogenes, and whether they were genetically similar or different. The provided presumptive Listeria cultures isolated from industrial processed food are conventionally assumed to be L. monocytogenes. All samples were cultured on brain heart infusion agar and broth first and then on blood agar. Later, hly gene amplification was applied. The provided culture phenotypically resembled L. monocytogenes as it caused haemolysis on blood agar plates; however, the absence of the hly gene revealed that they were genotypically different. 16S rRNA confirmed three species of Listeria species including L. grayi, L. welshimeri and L. ivanovii. The results from 16S rRNA sequencing confirmed the results obtained from hly gene amplification. Enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC PCR) confirmed that all bacterial cultures were isolated from different sources depending on their ERIC PCR profile variation.