Advantages of virulotyping foodborne pathogens over traditional identification and characterization methods

Authors: Gurtler, Joshua; DOYLE, MICHAEL - University Of Georgia; KORNACKI, JEFFREY - Kornacki Microbiology Solutions, Inc; Fratamico, Pina; Gehring, Andrew; Paoli, George

Submitted to: Foodborne Pathogens Virulence Factors and Host Susceptability
Publication Type: Book / Chapter
Publication Acceptance Date: 3/16/2017
Publication Date: 4/21/2017
Citation: Gurtler, J., Doyle, M.P., Kornacki, J.L., Fratamico, P.M., Gehring, A.G., Paoli, G. 2017. Advantages of virulotyping foodborne pathogens over traditional identification and characterization methods. Foodborne Pathogens Virulence Factors and Host Susceptability. New York, NY: Springer Publishing. p. 3-40.

Interpretive Summary: Food products are often tested for the presence of pathogenic bacteria by traditional microbiological methods. A potentially more accurate determination of whether a bacterium is pathogenic may be accomplished by testing for genetic virulence markers, which indicate whether the bacterium is truly a pathogen. These genetic markers are known as virulence factors and testing for these markers has been called virulotyping. The use of virulotyping could prevent some pathogenic bacteria, which may otherwise be thought to be harmless, from entering the food supply. On the other hand, virulotyping could also indicate that a bacterium thought to be harmless is, in fact, pathogenic to humans. The United States Department of Agriculture, Food Safety and Inspection Service currently tests raw non-intact beef, such as ground beef and mechanically tenderized beef and raw intact beef intended for non-intact use, such as beef manufacturing trim, for the presence of two virulence genes, as well as serotyping the isolates. This method could serve as a model for other applications of virulotyping.

Technical Abstract: This chapter provides an overview regarding the advantages of virulotyping over historic serology-based, PCR-based on genes that identify an organism, or enzymatic and biochemical-based analyses of foodborne pathogens in clinical diagnostics and food industry microbiology testing. Traditional identification and characterization methods are designed to detect a given genus, species, serovar or genetic variants of bacteria via enzymatic, genetic or biochemical characterization. Virulotyping is a technique that identifies specific virulence genes within the pathogen’s genome; thus having the discriminatory power to differentiate between a virulent and an avirulent (nonpathogenic) strain of bacterium within a species. As an example, the United States Department of Agriculture, Food Safety and Inspection Service (USDA-FSIS) methods for detection, isolation and identification of Shiga toxin producing E. coli (STEC) use the presence of the eae and stx genes along with specific identification of specifiec O-groups (O26, O45, O103, O111, O121, O145 and O157) that are associated with a majority of human illnesses to determine if one of these adulterant STEC is present in a raw beef verification sample. While there are an estimated 175,905 cases of foodborne STEC illnesses in the U.S. annually, the U.S. Centers for Disease Control and Prevention (CDC) reported that 5.9% (10,378) of laboratory-confirmed STEC illnesses reported to them in 2012 were caused by STEC that were not among the top seven serovars. While virulence testing for the top seven STEC serovars is just one example of potential advantages of virulotyping, further benefits may also be realized from virulotyping other common foodborne pathogens (e.g., Campylobacter spp., Salmonella enterica, and Listeria monocytogenes), should avirulent subgroups one day be identified. While PCR and microarray analyses are currently used to perform virulotyping, genome sequencing-based methods may be a more robust and discriminatory technique, when it becomes practicable for food safety testing and clinical diagnostics. A potential future virulotyping-based medical diagnostics and food testing system might be envisioned in the United States, which could prevent illnesses.