Application of the 5 '-nuclease PCR assay in evaluation and development ofmethods for quantitative detection of Campylobacter jejuni

Campylobacter jejuni is recognized as a leading human food-borne pathogen. Traditional diagnostic testing for C. jejuni is not reliable due to special growth requirements and the possibility that this bacterium can enter a vi able but nonculturable state. Nucleic acid-based tests have emerged as a us eful alternative to traditional enrichment testing. In this article, we pre sent a 5'-nuclease PCR assay for quantitative detection of C. jejuni and de scribe its evaluation. A probe including positions 381121 to 381206 of the published C. jejuni strain NCTC 11168 genome sequence was identified. When this probe was applied, the assay was positive for all of the isolates of C . jejuni tested (32 isolates, including the type strain) and negative for a ll other Campylobacter spp. (11 species tested) and several other bacteria (41 species tested). The total assay could be completed in 3 h with a detec tion limit of approximately 1 CFU. Quantification was linear over at least 6 log units. Quantitative detection methods are important for both research purposes and further development of C. jejuni detection methods. In this s tudy, we used the assay to investigate to what extent the PCR signals gener ated by heat-killed bacteria interfere,vith the detection of viable C. jeju ni after exposure at elevated temperatures for up to 5 days. An approach to the reduction of the PCR signal generated by dead bacteria was also invest igated by employing externally added DNases to selectively inactivate free DNA and exposed DNA in heat-killed bacteria. The results indicated relative ly good discrimination between exposed DNA from dead C. jejuni and protecte d DNA in living bacteria.