Detection by real-time PCR and conventional culture of Salmonella Typhimurium and Listeria monocytogenes adhered to stainless steel surfaces under dry conditions

Abstract

This study evaluated the capacity of real-time PCR and conventional culture methods to detect Salmonella enterica serovar Typhimurium and Listeria monocytogenes adhered to stainless steel surfaces used as food contact surfaces. The adhesion of the microorganisms to the surfaces was performed under dry conditions to represent the stress to which these pathogens can be subjected in the food processing environment. The samples were analyzed with various pre-enrichment times: S. Typhymurium (0, 6, and 18 h) and L. monocytogenes (0, 6, and 25 h) and with procedures concentrating or not concentrating the samples after the pre-enrichments. The results showed that real-time PCR obtained increased capacity than the conventional method to detect a low number of both pathogens, and real-time PCR even detected samples without pre-enrichment. However, pre-enrichment is recommended to avoid the detection of false positives from dead cells during adhesion and to ensure the absence of false negatives due to low initial concentrations. The concentration of the adhering bacteria increased the frequency in the detection of positive results for S. Typhimurium, but this effect was not observed in the case of L. monocytogenes.