Rapid detection of Salmonella enterica in food samples by a novel approach with combination of sample concentration and direct PCR

Foodborne salmonellosis remains a major economic burden worldwide and particularly for food industries. The diverse and complexity of food matrices pose great challenges for rapid and ultra-sensitive detection of Salmonella in food samples. In this study, combination of pathogen pre-concentration with rapid molecular identification is presented to overcome these challenges.

This combination enabled effective real-time PCR detection of low levels of Salmonella enterica serovar Typhimurium without culture enrichment. Anti-salmonella antibody, immobilized on protein AG-magnetic beads, could efficiently concentrate Salmonella Typhimurium with a capturing efficiency of 95%.

In the direct PCR, a strong linear relationship between bacteria concentration and the number of cycles was observed with a relative PCR efficiency of ∼92% resulting in a limit of detection (LoD) of ∼2 CFU/mL. Analysis of spiked food samples that include vegetable salad, egg yolk, egg white, whole egg and minced pork meat has validated the precision of the method.

A relative accuracy of 98.3% with a sensitivity of 91.6% and specificity of 100% was achieved in the Salmonella spiked food samples. The use of a Phusion hot start DNA polymerase with a high tolerance to possible PCR inhibitors allowed the integration of direct PCR, and thereby reducing the duration of analysis to less than 3 hours.

The Cohen's kappa index showed excellent agreement (0.88) signifying the capability of this method to overcome the food matrix effects in rapid and ultra-sensitive detection of Salmonella in food. This approach may lay a future platform for the integration into a Lab-on-a-chip system for online monitoring of foodborne pathogens.