Advantages of and limits to application of the polymerase chain reaction (PCR) to detection and typing of food-borne pathogenic bacteria

A brief cultural enrichment, followed by physical separation of the organisms from the culture and subsequent PCR using specific primers is a promising alternative to the conventional detection methods of pathogenic bacteria in foods. With limited workload, the method may provide confirmed results within 24 hours without the necessity to routinely isolate pure cultures. Use of PCR without prior cultural enrichment is of interest in the detection of bacteria that are difficult to cultivate, and of nonculturable or nonviable forms. However, for wider application in laboratories of food microbiology, the sensitivity of the latter method is unsatisfactory. Moreover, the time and effort required to concentrate and purify DNA from the samples makes it difficult to obtain the result within one working day. The PCR is an important tool to detect specific genes (especially, virulence genes) in pure cultures. Moreover, PCR-based typing methods have advantages (easily accessible reagents, few if any untypable strains) over typing methods based on phenotypic properties, and may thus assist in tracing back hygienically relevant organisms through the production chain. However, the reproducibility of electrophoretic patterns is a problem, particularly with the RAPD method. The methods described differ in their discriminatory power and the choice of a typing method (be it PCR-based or ,,conventional") is difficult because it must be based on the degree of genetic homogeneity and stability of the species or subspecies to be typed.