PCR Method Validated for Meat Salmonella Screening

DENMARK - A same-day real-time PCR method for screening of meat and carcass swabs for Salmonella was found to work well. The experiments have been published by Charlotta Löfström from the National Food Institute and colleagues in BMC Microbiology.

22 May 2009

3 minute read

Europe

Background

One of the major sources of human Salmonella infections is meat. Therefore, efficient and rapid monitoring of Salmonella in the meat production chain is necessary. Validation of alternative methods is needed to prove that the performance is equal to established methods. Very few of the published PCR methods for Salmonella have been validated in collaborative studies.

This study describes a validation including comparative and collaborative trials, based on the recommendations from the Nordic organisation for validation of alternative microbiological methods (NordVal) of a same-day, non-commercial real-time PCR method for detection of Salmonella in meat and carcass swabs.

Results

The comparative trial was performed against a reference method (NMKL-71:5, 1999) using artificially and naturally contaminated samples (60 minced veal and pork meat samples, 60 poultry neck-skins, and 120 pig carcass swabs).

The relative accuracy was 99 per cent, relative detection level 100 per cent, relative sensitivity 103 per cent and relative specificity 100 per cent.

The collaborative trial included six laboratories testing minced meat, poultry neck-skins, and carcass swabs as un-inoculated samples and samples artificially contaminated with 1 to 10 colony-forming units (cfu) in 25g, and 10 to 100 cfu in 25g.

Valid results were obtained from five of the laboratories and used for the statistical analysis. Apart from one of the non-inoculated samples being false positive with PCR for one of the laboratories, no false positive or false negative results were reported.

Partly based on results obtained in this study, the method has obtained NordVal approval for analysis of Salmonella in meat and carcass swabs.

The PCR method was transferred to a production laboratory and the performance was compared with the BAX Salmonella test on 39 pork samples artificially contaminated with Salmonella. There was no significant difference in the results obtained by the two methods.

Conclusions

The real-time PCR method for detection of Salmonella in meat and carcass swabs was validated in comparative and collaborative trials according to NordVal recommendations.

The PCR method was found to perform well.

The test is currently being implemented for screening of several hundred thousand samples per year at a number of major Danish slaughterhouses to shorten the post-slaughter storage time and facilitate the swift export of fresh meat.

Reference

Lofstrom C., M. Krause, M.H. Josefsen, F. Hansen and J. Hoorfar. 2009. Validation of a same-day real-time PCR method for screening of meat and carcass swabs for Salmonella. BMC Microbiology, 9:85. doi:10.1186/1471-2180-9-85.