Detection and differentiation of Salmonella Enteritidis and Salmonella Typhimurium by multiplex quantitative PCR from different poultry matrices

Salmonella detection with LAMP and qPCR and identification of serovars of interest by multiplex qPCR in poultry carcasses

Salmonella is present in the poultry production chain and is a major challenge in terms of food safety and animal health. The early Salmonella detection is one of the main tools to control and prevent the transmission of this pathogen. Microbiological isolation and serotyping to identify and differentiate Salmonella serovars are laborious processes, time-consuming, and expensive. Therefore, molecular diagnostic methods can be rapid and efficient alternatives to the detection of this pathogen. Thus, the aim herein was to standardize and evaluate the use of loop-mediated isothermal amplification (LAMP) in comparison with real-time PCR (qPCR) for detection of Salmonella associated with a multiplex qPCR for simultaneous identification and differentiation of S. Enteritidis, S. Typhimurium, S. Pullorum, and S. Gallinarum. The LAMP, qPCR, and multiplex qPCR assays were comparable in specificity. The three techniques were evaluated for specificity for 16 different serovars of Salmonella and for 37 strains of the serovars of interest. The limit of detection and the efficiency of the LAMP, qPCR, and multiplex qPCR reactions were determined. The techniques were applied to 33 samples of chicken carcasses and compared to the results of conventional microbiology for validation. As results, LAMP was specific in the detection of different Salmonella serovars but presented lower limit of detection ranging from 101 to 104 CFU/reaction. In comparison, qPCR could detect less cells (100 to 102 CFU/reaction), reaching equal specificity and better repeatability in the assays. The qPCR multiplexing for identification of the different serovars also showed good specificity, with the detection threshold between entre 101 and 102 CFU/reaction. The results obtained in the analyses on poultry carcasses suggested a correspondence between the results obtained in molecular methods and in conventional microbiology. Thus, the proposed assays are promising for the diagnosis of Salmonella in poultry carcasses, already proved to be faster and more efficient than conventional diagnostics techniques, being of great interest for poultry production, animal, and public health.

Multiplex Real-Time PCR for the Detection of Shiga Toxin-Producing Escherichia coli in Foods

Shiga toxin-producing Escherichia coli (STEC) is a group of human foodborne pathogens transmitted to humans through the consumption of different types of food. Their detection is mainly performed by targeting specific serogroups by classical microbiological methods and, later, by molecular typing with different techniques. The application of multiplex real-time PCR (qPCR) can significantly improve the turnaround time of the existing methodologies as in one single run it is possible to detect and characterize specific microorganisms. In the present chapter, a pentaplex qPCR assay is described for the identification of STEC which may also be applied for the rapid screening of these pathogens in different types of foods. The assay targets the most important virulence factors of these microorganisms, the genes stx1, stx2, and eae, along with the rfbE gene which encodes for the "O157" antigen as this is the most prevalent serogroup among all STEC, as well as an internal amplification control to rule out false-negative results due to qPCR inhibition.