Establishment and Application of a duplex real-time qPCR method for detection of Salmonella spp. and Serratia fonticola in imported feedstuffs

Abstract

Salmonella spp. is a high-risk bacterial pathogen that is monitored in imported animal-derived feedstuffs. Serratia fonticola is the bacterial species most frequently confused with Salmonella spp. in traditional identification methods based on biochemical characteristics, which are time-consuming and labor-intensive, and thus unsuitable for daily inspection and quarantine work. In this study, we established a duplex real-time qPCR method with invA-and gyrB-specific primers and probes corresponding to Salmonella spp. and S. fonticola. The method could simultaneously detect both pathogens in imported feedstuffs, with a minimum limit of detection for Salmonella spp. and S. fonticola of 197 copies/L and 145 copies/L, respectively (correlation coefficient R2 = 0.999 in both cases). The amplification efficiency for Salmonella spp. and S. fonticola was 98.346% and 96.49%, respectively. Detection of clinical samples was consistent with method GB/T 13091-2002, and all 20 artificially contaminated imported feed samples were positively identified. Thus, the developed duplex real-time qPCR assay displays high specificity and sensitivity, and can be used for the rapid and accurate detection of genomic DNA from Salmonella spp. and S. fonticola within hours. This represents a significant improvement in the efficiency of detection of both pathogens in imported feedstuffs.\n\nImportanceImported feedstuffs must be tested for pathogenic Salmonella species that represent a biological hazard. Various non-Salmonella colony-forming species belong to Enterobacteriaceae, and Serratia fonticola forms colonies of similar color and morphology to Salmonella spp., leading to confusion in daily quarantine tests. Traditional methods based on biochemical and serological characteristics are cumbersome and labor-intensive, and unable to fully support current quarantine testing demands. Thus, there is an urgent need to develop a rapid and accurate method for the effective identification of these pathogens. The duplex real-time qPCR method established herein can rapidly identify Salmonella spp. and S. fonticola, and has great potential for application to feed safety and prevention of exterior pathogens.