Rapid Detection of Viable <em>Listeria monocytogenes</em> in Chilled Pork

Scientists based in Nanjing describe a method to show the presence of live cells of the foodborne pathogen, L. monocytogenes, in chilled pork and to predict the approximate level of contamination by using an RNA-dependent real-time PCR method.

16 November 2011

3 minute read

By: Jackie Linden

In their paper published in the journal, Food Control, recently, Keping Ye of Nanjing Agricultural University and co-authors there and at Nanjing Normal University in China explain that the objective of their study was to develop an RNA-dependent real-time reverse-transcriptase PCR (real-time RT-PCR) method for the detection of Listeria monocytogenes in chilled pork without the need for pre-enrichment steps, and the soundness of the method was simultaneously validated and evaluated by DNA-based real-time PCR and traditional culture methods.

For specificity testing, a lack of amplification signals and no Tm peak at around 78.37°C were obtained from any of 41 other bacterial strains associated with meat species under the conditions used.

The R2 and efficiency of standard curves constructed by 10-fold serial dilutions of pure L. monocytogenes were, respectively, 0.995 and 90.1 per cent; lower than that of the DNA-based assay.

The detection limit was up to 100 colony-forming units (cfu) per millilitre in both pure culture and in artificially contaminated chilled pork samples.

Quantitative detection showed that the RNA-based assay obtained relatively accurate results when samples had undergone treatments (such as high pressure), but without treatment, the results showed a slight deviation compared with plate counts.

The RNA-dependent real-time RT-PCR method developed in this study was found to be rapid and sensitive and should be useful for reliable detection of viable L. monocytogenes in chilled pork, especially for pre-treated samples, concluded Ye and co-authors. However, they added, the method cannot be recommended to quantify L. monocytogenes accurately but only to show the presence of live cells and approximately predict its level of contamination.

Reference

Ye K., Q. Zhang, Y. Jiang, X. Xu, J. Cao and G. Zhou. 2011. Rapid detection of viable Listeria monocytogenes in chilled pork by real-time reverse-transcriptase PCR. Food Control, 25 (1), 117-124.