Evaluation of PCR assay to detect stn gene of Salmonella in chicken meat and lettuce samples

Abstract

Consumption of Salmonella-contaminated foods causes foodborne illness, which is a major problem of public health in developed and developing countries. Chicken meat and lettuce have been reported to be contaminated with this pathogen. Although the culture-based method followed by biochemical confirmation is a standard method, there are many limitations particularly time-consuming and low sensitivity. In this research, we used a developed PCR assay from our previous study indicating high sensitivity and specificity to evaluate the efficacy of Salmonella detection from chicken meats and lettuces based on Salmonella enterotoxin gene (stn) target. The limits of detection from artificial contamination of chicken meat and lettuce were studied. With an overnight enrichment step in Buffered Peptone Water (BPW) performed prior to the PCR assay, it could detect Salmonella, which was 1 CFU/ 25 g chicken meat and 100 CFU/ 50 g lettuce, respectively. Total of 120 food samples including each of chicken meat and lettuce for 60 samples from local markets in Bangkok and other provinces in central part of Thailand were tested with PCR assay of stn gene and culture methods. Using the culture method as gold standard, the sensitivity and specificity for detection of Salmonella by the PCR method were 84.6 and 90.5 % in chicken meat and 69.2 and 97.9 % in lettuce, respectively. Thus, our developed PCR assay can be applied for rapid Salmonella detection in food samples especially in chicken meats.