Strategies for Optimizing Salmonella Control
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Transcript of Strategies for Optimizing Salmonella Control
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Strategies for Optimizing Salmonella Control
Steven C. Ricke
Director of the Center for Food Safety
Wray Endowed Chair in Food SafetyDept. of Food Science
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Salmonella -Why Do We Care?
• Infection and disease in humans- Mortalities- Cost $billions each year
• Survivability in the Environment – Recontaminate food animals– Unpredictable reservoirs - pets– Difficult timeframe for traceback
• Virulence and antibiotic resistance– Pathogenic phenotype– Dissemination of antibiotic resistance
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What makes Salmonella pathogenic?
– Pathogenicity = Ability to cause disease in the host
– Virulence = Potency of infection
– Virulence genes = Anything in the bacterial genome associated with pathogenesis
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Regulation of Virulence in Salmonella
External signals: pH, O2, iron, osmolarity, cation, organic acids, in vivo signals
Induction of virulence genes = pathogenesis
Pathogenesis = stress adaptation, adhesion, invasion, macrophage survival
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Complexity of Salmonella Pathogenic Response• Multiple factors in the gastrointestinal tract
• Variability in human/animal host response to Salmonella
• Multiple environmental matrices during food processing = potential cross protection
• Need: more comprehensive genetics
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Sequence of Pathogen Genomes
• Good news: Completed for more and more Salmonella serotypes
• Bad news: Potential information is overwhelming!!
• How do we use this tool kit to meet the needs of the food industry?
– Tracking: Comparing sequences among isolates – Functional genomics: Identifying essential genes with unique functions for
pathogenesis
– Quantifying gene expression to understand regulation of pathogenesis
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Quantifying Gene Expression: Transcriptional profiling of pathogens
Transcriptional Profiling Overview
Hybridization of labeled probes on microarray slide
Measurement of Fluorescencein 2 channels
red/green
Data analysisIdentification of
differentiallyexpressed genes
Control
Test
RNA extraction from samples
RNA
FluorescentlyLabeled cDNA Probes
cDNA
Application of microarray analysis of foodborne Salmonella in poultry production: A review. S.C. Ricke , A. Khatiwara , and Y.M. Kwon. 2013 Poultry Science 92 :2243–2250.
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Genomic Screening for Cross-Protection Potential in Salmonella to Antimicrobials A, B, or C
Genes A-Resist Genes B-Resist Genes C-Resist
Genes A-Resist Genes B-Resist
Genes C-Resist
No Cross protection = Optimal
Extensive Cross protection = Not good
Application of microarray analysis of foodborne Salmonella in poultry production: A review. S.C. Ricke , A. Khatiwara , and Y.M. Kwon. 2013 Poultry Science 92 :2243–2250.
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Cross Protection - Genomic Studies
• Combinations of heat and organic acids-Decrease viability: synergism-pH: 4.0 vs. 7.0-Acid type: Acetate vs. propionate-Membrane disruption: K ion leakage
• Transcriptome responses: – pH 4.0 and 55 C– Acetate and propionate similar genetically– Repression of heat shock genes– Membrane damage is key
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Applications - Genomic Studies• Sudden shifts in pH may increase S. Typhimurium
virulence level in a food matrix-How long?-Acid type
• Thermal interaction with virulence should be considered
• Chemical composition of food before and after physical processing may be a factor in virulence response
Growth and transcriptional response of Salmonella Typhimurium LT2 to glucose–lysine-based Maillard reaction products generated under low water activity conditions. V. I. Chalova, O. Hernández-Hernández, A. Muthaiyan, S.A. Sirsat, S. Natesan, M. L. Sanz, F. J. Moreno, C. A. O'Bryan, P. G. Crandall, S.C. Ricke. 2012. Food Res. International. 45: 1044-1053.
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How Do We Use The Results? Examples for Application of Salmonella Genomics
- Cost effective control measures = High throughput screening for designing optimal multiple hurdles
- Risk assessment or How safe does it need to be? Better models for food processing impact on infection potential
-Vaccine technologies: Designing optimal vaccine targets
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Thank You