Isolation and detection of Listeria spp, Salmonella spp and Yersinia spp using a simultaneous enrichment step followed by a surface adhesion immunofluorescent technique.

The use of a rapid surface adhesion immunofluorescent (SAIF) technique for the isolation of three pathogens using a single enrichment step from broth and enriched meat cultures was investigated. Buffered peptone water (BPW, 225 ml) was inoculated with Listeria monocytogenes, Salmonella enteritidis and Yersinia enterocolitica to a level of 10 cfu ml(-1) and incubated overnight at 30 degrees C. Minced beef samples (25 g) were inoculated with the three pathogens to a level of 100 cfu g(-1) and incubated overnight at 30 degrees C in BPW (225 ml). Pathogens were isolated by surface adhesion to a polycarbonate membrane which was immersed in the enriched culture. The pathogens were detected using membrane counts (rinse and immunofluorescent) and standard plate counts. It was noted that the attachment of the three pathogens to the membrane was considerably enhanced when compared with single inoculum experiments and the reasons and implications of this for the rapid method are discussed. A small selection of naturally contaminated retail samples (n = 60) was tested for the presence of L. monocytogenes and S. enteritidis using a simultaneous enrichment step with SAIF detection and a standard cultural method of detection. A good correlation was found between both methods for L. monocytogenes (r2 = 0.91, RSD = 0.26) and S. enteritidis (r2 = 0.89, RSD = 0.28). This indicates that simultaneous analysis of these two pathogens could be carried out using the SAIF assay.