Rapid assay for pathogenic Salmonella organisms by immunofluorescence flow cytometry

Multi-parameter flow cytometry was investigated for the rapid detection of specific serotypes of salmonellas (S. typhimurium and S. montevideo) labelled with fluorescent monoclonal antibodies, both in pure culture and in a typical food matrix (full-fat milk). In all cases, the method was accurate to levels of below 10(4) target cells per ml for a total assay time of about 30 min. After 6 h non-selective enrichment in the presence of a 10,000-fold excess of competing micro-organisms (Escherichia coli) the corresponding detection limit was about 20 cells ml-1. These results suggest that flow cytometry has significant potential for the detection of pathogenic micro-organisms in the food industry.