THE USE OF A PCR-GENERATED INVA PROBE FOR THE DETECTION OF SALMONELLASPP IN ARTIFICIALLY AND NATURALLY CONTAMINATED FOODS

Part of the invasion A gene (invA) of salmonellae (Rahn et al., 1992) was amplified and labelled simultaneously with digoxigenin by the poly merase chain reaction (PCR). This was used as gene probe for a colony hybridization assay which included nitrocellulose filter incubation on modified Rambach agar. 312 Salmonella and 268 non-Salmonella strains were hybridized with the invA probe. No false-negative or false-positi ve results were obtained. In 11 beef samples, which had been contamina ted artificially with Salmonella, the test strain was recovered quanti tatively with the invA probe. Salmonellae could be detected in 29 samp les of 104 further foods of animal origin by means of the gene probe a ssay in contrast to 27 samples which were positive by the standard met hod. The invA probe assay allows for the quantitative estimation of Sa lmonella in fresh meat samples within 48 h. However, with frozen sampl es a pre-enrichment step is necessary.