Demonstration of the effective performance of a combined enrichment/real-time PCR method targeting the prfA gene of Listeria monocytogenes by testing fresh naturally contaminated acid curd cheese

Abstract

Aims: A rapid real-time PCR-based method for the detection of Listeria monocytogenes was applied to the examination of 44 Quargel cheese samples from a recent outbreak in Austria and compared to the standard method according to ISO-16140.

Methods and results: The combined enrichment/real-time PCR method amplifying the prfA locus was performed according to [Rossmanith et al.(2006) Res Microbiol, 157, 763-771]. Qualitative and quantitative examination of the samples was performed according to the standard method ISO-11290. Comparison of the combined enrichment/real-time PCR method with ISO-11290 resulted in 100% relative accuracy, 100% relative sensitivity and 100% relative specificity.

Conclusions: A previously published study describing the validation of the method, including samples after storage at -80 degrees C, resulted in lower performance values. In contrast, the samples were stored at +4 degrees C in this study. The results of this study indicate an effect of storage, thus masking the true performance of the method.

Significance and impact of the study: The results of this study are discussed together with the previously published data to demonstrate the excellent qualities of this rapid (< or = 30 h) method when applied to fresh specimens stored at +4 degrees C.