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Escherichia coli O157:H7 and Shiga
toxin-converting bacteriophage
Edward G. Dudley, Ph.D
Department of Food Science
[email protected]
Escherichia coli O157:H7 history
and food safety issues
Foodborne illness affects 48 million annually
http://wwwnc.cdc.gov/eid/article/17/1/pdfs/p2-1101.pdf
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
5
Images from Dr. Erika A. Taylor’s website
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”
<30% of genes are shared in all
Escherichia coli strains
Welch R A et al. PNAS 2002;99:17020-17024
©2002 by National Academy of Sciences
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 botulinum
Staphylococcus aureus
Vibrio cholerae
Salmonella enterica
Shigella flexneri
Other Escherichia coli
Escherichia coli O157:H7 carry an
active phage that encodes a toxin
Recombination Regulation
PR’ Stx2A/B
cI = repressor protein
Lysis
Capsid/tail fiber
Plunkett III, G., D. J. Rose, T. J. Durfee,
and F. R. Blattner. 1999. Sequence of
Shiga toxin 2 phage 933W from Escherichia
coli O157: H7: Shiga toxin as a phage
late-gene product. J. Bacteriol. 181:17671778.
DNA damaging agents induce phage
and increase toxin production
Ciprofloxacin (DNA gyrase)
14
Shiga toxin blocks protein synthesis by
targeting 28S rRNA
One “A” subunit (319 amino acids)
http://journal.frontiersin.org/Journal/10.3389/fcimb.2012.00081/full
AB5 toxin
Five “B” subunits (91 amino acids)
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
+
Commensal
(non-pathogenic)
Plate counts
ELISA for toxin production
Shiga toxin levels affected by other
intestinal E. coli strains
Germ free mouse experiments
Control
Colonize with E. coli C600
Day -7
Test
Plate feces
Sacrifice 5 mice
Inoculate with E. coli O157:H7
Day 0
Day 1
Day 6
Increased virulence of E. coli O157:H7
in presence of non-pathogenic E. coli
Acute renal tubular necrosis
in mice colonized by PA2
with or without C600
4
p=0.0077
ATN score
3
2
1
0
C600
PA2
PA2+
C600
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