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Escherichia coli O157:H7 and Shiga toxin-converting bacteriophage Edward G. Dudley, Ph.D Department...
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Transcript of Escherichia coli O157:H7 and Shiga toxin-converting bacteriophage Edward G. Dudley, Ph.D Department...
Escherichia coli O157:H7 and Shiga toxin-converting bacteriophage
Edward G. Dudley, Ph.DDepartment of Food Science
Escherichia coli O157:H7 history and food safety issues
http://wwwnc.cdc.gov/eid/article/17/1/pdfs/p2-1101.pdf
Foodborne illness affects 48 million annually
Escherichia coli O157:H7 is a recently discovered foodborne pathogen
E. coli are first characterized by serotyping
• O-antigen– Somatic antigen– >170 known
• H-antigen– Flagellar antigen– >60 known
• E. coli O157:H7
Images from Dr. Erika A. Taylor’s website 5
Transmission of O157:H7 to humans usually starts with cattle
Nougayrède et al., 2003
Control of E. coli O157:H7 in food supply starts at processing plant
Beef represents ~50% of foodborne cases of disease
Evolution of one of the defining virulence factors of E. coli O157:H7
Escherichia coli evolves via genomic insertions and deletions
“horizontal gene transfer”
Welch R A et al. PNAS 2002;99:17020-17024
©2002 by National Academy of Sciences
<30% of genes are shared in all Escherichia coli strains
Temperate phage are drivers of most genomic diversity in Escherichia coli
diagram from Dr. Ken Todar
Many virulence factors are phage encoded
Foodborne pathogens:
Clostridium botulinumStaphylococcus aureusVibrio choleraeSalmonella entericaShigella flexneriOther Escherichia coli
Plunkett III, G., D. J. Rose, T. J. Durfee, and F. R. Blattner. 1999. Sequence ofShiga toxin 2 phage 933W from Escherichia coli O157: H7: Shiga toxin as a phagelate-gene product. J. Bacteriol. 181:1767-1778.
Recombination Regulation PR’ Stx2A/B Lysis Capsid/tail fiber
Escherichia coli O157:H7 carry an active phage that encodes a toxin
cI = repressor protein
DNA damaging agents induce phage and increase toxin production
14
Ciprofloxacin (DNA gyrase)
One “A” subunit (319 amino acids)
Five “B” subunits (91 amino acids)
http://journal.frontiersin.org/Journal/10.3389/fcimb.2012.00081/full
Shiga toxin blocks protein synthesis by targeting 28S rRNA
AB5 toxin
Do other organisms change amount of toxin produced?
Do gut organisms affect virulence of Escherichia coli O157:H7?
Experimental setup
E. coli O157:H7 strain PA2
Plate counts ELISA for toxin production
Commensal(non-pathogenic)
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Shiga toxin levels affected by other intestinal E. coli strains
Germ free mouse experiments
Colonize with E. coli C600
Day -7
Inoculate with E. coli O157:H7
Day 0
Control
Test
Day 1 Day 6
Plate fecesSacrifice 5 mice
Increased virulence of E. coli O157:H7 in presence of non-pathogenic E. coli
Growing threats to the food supply
The Shiga toxin phage can mobilize to other E. coli, creating new pathogens
enteroaggregative Escherichia coli
• Serotype O104:H4• Ill: 4,321. HUS: ~30% of cases. Dead: 50
Several “new” O-groups are of increasing concern
Year Serogroup Location Food/event # ill
2014 O111 Minnesota Cabbage (Applebees and Yard House restaurants)
13
O121 5 States Sprouts (Jimmy Johns, Pita Pit)
19
2013 O121 9 States (including PA)
Farm Rich Products frozen snacks
35
2012 O145 5 States Unknown 18
2011 O26 OH, PA, AL Sprouts (Jimmy Johns) 29
2010 O145 5 States (including PA)
Shredded romaine lettuce
33
The “Big Six”: Shiga toxin E. coli of serogroups O26, O45, O103, O111, O121, O145