Comparison of PI-PLC based assays and PCR along with in vivo pathogenicity tests for rapid detection of pathogenic Listeria monocytogenes

A study was carried out to compare phosphatidylinositol specific phospholipase C (PI-PLC) assay, chromogenic medium ALOA and a PCR for virulence associated genes (the plcA, hlyA and prfA) with mice and chick embryo inoculation for detection of pathogenic Listeria monocytogenes from milk and ready-to-eat (RTE) indigenous milk products. Eighteen strains of L. monocytogenes were isolated. A good correlation was observed among all the assays. ALOA exhibited distinct results (bluish green colonies with halo formation) within 24–48 h however; enzymatic activity was expressed on PI-PLC assay by 4 days of inoculation. About 93% hemolytic L. monocytogenes isolates were positive for genotypic and phenotypic expression of plcA gene and also proved lethal to mice and chick embryo. The detection of PI-PLC activity on ALOA with PCR targeting the hlyA and plcA genes would be reliable in vitro alternatives to in vivo assays for detecting pathogenic L. monocytogenes.