E.coli O157:H7Marie Schneiders| VM 811 | Michigan State University

E. Coli O157:H7 - part of a subset of gram negative STEC (Shiga Toxin Escherichia coli) bacteria called EHEC

Characteristics

• EHEC: Enterohemorrhagic E. coli

• Characterized by production of Stx 1 and/or 2 and presence of LEE

• Facultative Anaerobe

Jack in the Box Incident of 1993

• Implicated in a McDonald’s out break in 1982 - at this time the organism was considered rare

• 1993: 732 people infected after eating hamburgers at 73 Jack in the Box restaurants in California, Idaho, Washington, and Nevada

• The majority of victims were children under the age of 10

• 4 children died

• 178 other victims were left permanently damaged

The largest outbreak in the world took place in Japan in 1996

The cause of the outbreak was white radish sprouts

6,309 school children and 92 school staff members became ill

By August 9,578 cases were reported and 11 people died

Sources of E. coli O157:H7

Raw and undercooked ground beef (most commonly implicated)

Water (potable, well, and recreational)

Bagged lettuce, spinach, and alfalfa sprouts

Yogurt, mayonnaise, fermented sausages, cheese, unpasteurized fruit juices

Frozen cookie dough

Virulence Factors

Shiga Toxin• Stx 1 nearly identical to that

produced by Shigella dysenteriae Type I

• Stx 2 most often associated with HUS (hemolytic uremic syndrome) – characterized by renal failure

Presence of LEE

• “Locus for enterocyte effacement”

• Encodes for intimin – a protein that enables bacterial attachment to epithelial cells

Other• Horizontal gene transfer

• Several other putative virulence factors, including enterohemolysin

• role of these factors in pathogenesis remains undetermined

Intimin receptor (Tir) translocates into the host cell and inserts itself into the host-cell plasma membrane

Receptor interacts with intimin on the bacterial surface firmly anchoring the bacterium to the host cell

Human Exposure to E.coli O157:H7

• FSIS (Food Safety & Inspection Service) estimates that 99.993% and 99.982% of cooked ground beef in low and high prevalence seasons respectively are not expected to have surviving E. coli O157:H7 organisms present

• FSIS estimates that in grinder loads consisting of 2,000 lbs. raw trim (combo) between 40% and 88% of these loads contained one or more E. coli O157:H7 in the low prevalence season and 61% to 94% in the high prevalence season

Frequency

• ~63,000 cases of EHEC infections in the U.S. yearly according to the CDC

• Ground beef continues to be implicated in most infections

• Contaminated produce is on the rise as a cause of infection

Infectious dose, clinical signs, and symptoms.

Estimated to be 10-100

cells

Infectious Dose

Symptoms typically

appear in 3-4 day, but can range 1-9

days

Incubation Period

asymptomatic, to mild

diarrhea, to severe

complications

Mild Symptoms

Hemorrhagic colitis

Hemolytic Uremic

Syndrome

Acute Symptoms

Hemorrhagic colitis and HUS

o Hemorrhagic Colitis

o Severe abdominal cramps, nausea, vomiting, diarrhea that is initially watery

o Diarrhea becomes bloody and may look like it consists entirely of blood and occurs every 15-30 minutes

o 3% - 7% of HC cases progress to HUS

o Duration of symptoms is 2-9 days with an average of 8

o HUS is the premature destruction of red blood cells which impede the filtering function of kidneys

o May cause kidney failure, but if properly treated in a healthy individual a full recovery may be expected

Detection and Diagnosis

• In raw, ground beef:

• Real-time PCR with Immuno-magnetic separation

• ELISA, VIP, chromogenic agars

• In symptomatic patients:

• Plate bloody stool sample on to Phenol Red Sorbitol agar – O157 does not ferment sorbitol

• Serologically confirm isolates from agar using O157 and H7 antigens

Host Defense

• Mucins, AMPs, and members of the intestinal microbiota

• Mucins create a dynamic physical barrier

• Anti-microbial peptites are effectors of the innate immune response

• Resident microbiota provide a microbial barrier against pathogens

• Bacteria that originated from the intestinal microbiota have the capacity for interfering with or block the process of pathogenicity of enteric bacterial pathogens

Control: In-Vivo

• Competetive Exlclsuion

• No field trials yet

• Beta-agonists (Ractopamine)

• Illegal to use almost everywhere but in the U.S. & questionable results

• Fasting

• Pre and Post Transportation

• Sudden feed switch to hay

• Results in lower slaughter weight

• Direct Fed Microbials (DFM)

• Probiotics

Control: Pre-harvest

• Clean water

• Clean feed

• Clean environment

• Separate housing of calves and heifers or reduced animal density

• Biosecurity – wildlife exclusion to the fullest extent possible

• Bacteriophage sprayed on hide of live cattle in holding pens

Control: Slaughter

• Sanitary Dress

• Sanitary Hide Removal

• Bunging

• Rodding the Weasand

• HACCP Program

• Interventions

• Steam cabinets

• Anti-microbial carcass wash

Control : Processing & Sampling

• N60 trim sampling - 60 slices per lot

• 1 Lot = 5 combos

• New single-combo “Shaver” sampling

• N60+

• 1 combo = 1 lot

• Mechanical coring of 5 sites in a single combo using a drill and specialized drill head

• Each combo tested at the lab using RT-PCR

• Positive combos removed from food supply - sold to cook or rendered.

Control: Consumer End

• Practice proper hygiene

• Cook meats thoroughly

• Prevent cross-contamination

• Avoid consuming raw or unpasteurized dairy products or juices

References

• http://en.wikipedia.org/wiki/1993_Jack_in_the_Box_E._coli_outbreak

• http://www.mayoclinic.org/diseases-conditions/hemolytic-uremic-syndrome/basics/definition/con-20029487

• http://www.nature.com/nature/journal/v449/n7164/fig_tab/nature06247_F2.html

• http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1471992/

• http://www.fsis.usda.gov/OPPDE/rdad/FRPubs/00-023N/00-023NReport.pdf

• http://www.fsis.usda.gov/wps/wcm/connect/d5314cc7-1ef7-4586-bca2-f2ed86d9532f/Reducing-Ecoli-Shedding-in-Cattle.pdf?MOD=AJPERES

• http://www.fsis.usda.gov/OPPDE/rdad/FSISDirectives/6410.1.pdf

• http://www.ncbi.nlm.nih.gov/pubmed/24751204

• http://www.cdc.gov/Features/EcoliInfection/