2011 Annual Report
1a.Objectives (from AD-416)
Objective 1: Develop rapid and effective means to separate and concentrate targeted pathogens from food matrices that can be coupled to very rapid detection methods such as real-time PCR.
1A. Develop filtration/centrifugation methods for separating and concentrating pathogenic Escherichia, Salmonella, Listeria, and Campylobacter spp. from a variety of food matrices. Optimize reagents, apparatus and conditions to achieve maximum speed and recovery with minimum detection limits.
1B. Develop DNA extraction methods providing rapid, efficient, unbiased recovery of inhibitor-free DNA from a variety of pathogens.
Objective 2: Examine environmental factors and microbiological culture conditions affecting genotypes or phenotypes that are important for virulence, isolation, or detection of foodborne pathogens.
2A. Detection of foodborne threat agents (model system- pathogenic Yersinia spp.).
2B. Isolation and detection of foodborne pathogens maintaining mobile genetic elements.
2C. Enrichment of pathogens while maintaining mobile genetic elements.
Objective 3: Develop protein- and nucleic acid-based methods for the multiplexed detection and characterization of food-borne pathogens.
3A. Protein-based microarray and other multiplexed methods for the analysis of foodborne pathogenic bacteria.
3B. Oligonucleotide-based microarray for multiple pathogen detection and characterization.
3C. Multiplex real-time PCR for multiple pathogen identification and quantification.
Objective 4: Develop typing methods for pathogens of concern to associated food regulatory agencies.
4A. Develop Restriction Fragment Sequence Polymorphism method for typing.
4B. Fractionation of a naïve library of biorecognition elements for bacterial typing-An alternative to “molecular typing.”
1b.Approach (from AD-416)
This project plan has multiple goals that are distinct yet may be combined to generate improved, rapid techniques for the analysis of foodborne pathogenic bacteria (e.g., Campylobacter, E. coli, Listeria, Salmonella, and Yersinia spp.). Compared to traditional plate culture techniques, rapid methods for bacterial detection and typing [identification] primarily suffer from relatively poor sensitivity and/or selectivity. To improve detection limits for oligonucleotides using DNA microarray or multiplex RT-PCR, improved methods for DNA extraction, including an optimized alkaline/detergent reagent, will be developed for efficient extraction of nucleic acid from bacteria. Leukocyte removal filters will be used to separate bacteria from food matrices and concentrate the cells allowing for improved limits of detection by antibody microarray and/or time-resolved fluorescence. Culture enrichment conditions (e.g., slightly acidic pH, millimolar concentrations of calcium ion, with or without Irgasan) will be initially optimized for a model pathogenic bacterium (Yersinia) with the intent of concentrating the bacteria from the sample while maintaining mobile genetic elements [plasmids] required for expression of key genotypic and phenotypic markers. Prior to detection/typing with biosensor platforms, enriched Yersinia spp. will be carefully isolated and assessed for maintenance of virulence plasmids using organic dyes (crystal violet and/or Congo red) in conjunction with low calcium plating media. Novel biorecognition elements (initially, single chain variable fragment antibodies fractionated from naive phage display libraries) will be custom generated to improve accuracy of biosensor-based detection or phenotyping platforms (e.g., microarrays) for targeted pathogens. In addition, an abbreviated restriction fragment sequence polymorphism method will be developed and assessed as a novel genotyping method. Promising technologies will be directed towards usage by food producers and regulatory agencies for food safety monitoring and follow-up investigations.
This project was going through the OSQR review process during FY 2011. Progress addressed by SYs working on this project are documented in the reports for 1935-42000-058-00D or 1935-42000-062-00D.
Bhaduri, S. 2011. Effect of salt and acidic pH on the stability of virulence plasmid (pYV) in Yersinia enterocolitica and expression of virulence-associated characteristics. Food Microbiology. 28:171-173.
Bhaduri, S., Chaney, K.J., Smith, J.L. 2011. A procedure for monitoring the presence of the virulence plasmid (pYV) in Yersinia pestis under culture conditions. Foodborne Pathogens and Disease. 8:459-463.