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


Peter Rossmanith, Christian Doppler Laboratory for Molecular Food Analytics, Veterinärplatz 1, 1210 Vienna, Austria.


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°C, resulted in lower performance values. In contrast, the samples were stored at +4°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 (≤30 h) method when applied to fresh specimens stored at +4°C.