Lecture 13 - Detection, Identification and analysis of...

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Detection, Identification and analysis of Foodborne Pathogens
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Traditional Methods Gold standard Conventional methods Labor intensive Time consuming Costly Rapid methods Results in less time Reduce cost
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Rapid Methods Immuno-based assays ELISA Immunochromatographic or dipstick assays DNA-based assays PCR DNA hybridizations DNA microarrays
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Zero tolerance policy Listeria monocytogenes in ready to eat products Escherichia coli O157:H7 in non-intact fresh beef products Methods have to detect 1 colony- forming unit
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Problems Non-uniform distribution of pathogens Low level of target pathogen Interference of food matrix Injured organisms
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Molecular tools Beyond just presence/absence Deeper questions Genes involved in pathogenesis, persistence etc Fully determine microflora and relationship Development of better tests Intervention strategies
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Culture based methods Conventional Enrichment Plating Differential/selective Colony confirmations 5 or more days Enumeration MPN APC Injured bacteria
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Immunological Testing Antigen and Antibody reaction Sandwich ELISA assay is most popular Examples VIDAS (bioMerieux) EIA (BioControl) Reveal (Neogen) Rapidchek (SDI) Interference with colored pigments, less sensitive
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Nucleic acid based methods DNA hybridization Polymerase chain reaction Real-time PCR Reverse transcriptase PCR Multiplex PCR PCR on a chip DNA microarrays
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• Complete genomic sequence of strains discussed (bacteria and viruses) • Bacteria have 3,000,000-6,000,000 bp per genome • Complete genomic sequence gives a complete parts list of genes for an organism • Once one has the sequence then the genes coding for ribosomal RNA, transfer RNA and protein can be predicted Genomics
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Example of what we have learned from genomics E. coli O157:H7 has about 33% more genes than does the non-pathogenic lab strain E. coli K-12 Many of these genes in E. coli O157:H7 and not in E. coli K-12 potentially have a role in pathogenicity However, some genes in
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Lecture 13 - Detection, Identification and analysis of...

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