MOLECULAR CHARACTERIZATION OF PATHOGENS AND THEIR RESPONSES TO ENVIRONMENTAL FACTORS
Location: Molecular Characterization of Foodborne Pathogens
Title: Comprehensive approaches for molecular biomarker discovery for the detection and identification of Cronobacter spp. (Enterobacter sakazakii), Salmonella, and other foodborne pathogens
Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 2, 2011
Publication Date: March 1, 2011
Citation: Yan, X., Gurtler, J., Fratamico, P.M., Hu, J., Gunther, N.W., Juneja, V.K., Huang, L. 2011. Comprehensive approaches for molecular biomarker discovery for the detection and identification of Cronobacter spp. (Enterobacter sakazakii), Salmonella, and other foodborne pathogens. Applied and Environmental Microbiology. 77:1833-1843.
Interpretive Summary: Cronobacter and Salmonella are two bacteria found as contaminants of powdered infant milk. Unfortunately, these two types of bacteria present a considerable health risk to infants who might become infected by consumption of contaminated infant formula milk. Therefore, to ensure the safety of powdered infant milk, a method was developed to detect and identify Cronobacter and Salmonella when they are contaminating infant formula based on the unique genes that they carry. This research was able to identify a unique signature in both Cronobacter and Salmonella that can be used to differentiate these harmful bacteria from other harmless bacteria in food and the environment. A direct and simple method for detecting the presence of the unique gene signature for Cronobacter and Salmonella in food products is described by this research. This has resulted in the production of a new technique with good potential for improving the safety of powdered infant milk and the children dependent on this product from life threatening infections caused by Cronobacter and Salmonella.
Cronobacter spp. (formerly Enterobacter sakazakii) and Salmonella are increasingly implicated as important bacterial contaminants in low-moisture food products, including powdered infant formula. Estimates indicate that 40-80% of infants infected with C. sakazakii and/or Salmonella in the U.S. may not survive the illness. A systematic approach, combining literature-based data mining, comparative genome analysis, and the direct sequencing of PCR products of specific biomarker genes was used to construct an initial collection of genes to be targeted. These targeted genes, particularly genes producing virulence factors and genes responsible for unique phenotypes have the potential to function as biomarkers for the detection and identification of Cronobacter spp., Salmonella, and the other foodborne pathogens in low-moisture food products. In this paper, a chitinase gene, a well-studied virulence factor in fungi, plants, and bacteria, was used to confirm this approach to biomarker discovery. We found that the chitinase gene has very low sequence variability and/or polymorphism between Cronobacter spp. and Salmonella while differing significantly in other foodborne pathogens, either by sequence blasting or experimental testing, including PCR amplification and direct sequencing. Among the foodborne pathogens tested, only Salmonella, Citrobacter, and Cronobacter spp. have a similar chitinase or chitinase-like gene, as determined by computational blasting and PCR.