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

dudley@psu.edu

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