Immuno-detection and differentiation of Listeria monocytogenes and Listeria ivanovii in stone fruits

Aims The aim of this study was to develop a rapid detection and differentiation method for pathogenic Listeria species in stone fruits. Methods and Results We utilized activated charcoal enrichment media (ACM) to induce overexpression and hypersecretion of pathogenic Listeria virulence proteins which can subsequently be detected via immunoblot analysis. Plum and nectarine slices spiked with either L. monocytogenes or L. ivanovii were incubated in pre-enrichment broth followed by enrichment in ACM. Secreted proteins were precipitated and subjected to SDS-PAGE and immunoblot analysis using a combination of L. monocytogenes-specific antibody (alpha-listeriolysin O) and antibody specific for both L. monocytogenes and L. ivanovii (alpha-Internalin C). As low as 1 CFU per gram of L. monocytogenes in plum and nectarine was detected, whereas a detection limit of 10 CFU per gram was achieved for L. ivanovii in each food tested following a 20-h enrichment period. Nonpathogenic Listeria species and non-Listeria bacterial pathogens tested were negative. Conclusions These results demonstrate the highly sensitive and specific nature of the detection method for pathogenic Listeria in stone fruits using activated charcoal enrichment as well as the capability to discriminate between L. monocytogenes and L. ivanovii. Significance and Impact of the Study This method is the first to identify and differentiate L. monocytogenes and L. ivanovii in select stone fruit enrichments within 24 h using immunological techniques. The rapidity and sensitivity of the method could aid in the reduction of exposure to the public in the event of an outbreak and expedite the administration of appropriate antibiotics to infected individuals.