Shiga Toxin

Overview

Entero-hemorrhagic Escherichia Coli (EHEC) is an important species of diarrheagenic E. coli due to their ability to produce Shiga toxin (Stx). E. coli serotype 0157 is the most common strain implicated in outbreaks of Shiga toxin producing E. coli (STEC),, Other strains also can produce the toxin, and these are collectively known as Non-0157 STEC.  Infection with STEC can cause a wide variety of syndromes including diarrhea, hemorrhagic colitis and hemolytic uremic syndrome (HUS). The toxins are members of AB5 protein toxins where A represents an enzymatically active subunit and B is the binding subunit. Binding subunits in Stx have the affinity to the cellular receptors Gb3 present in several organs such as kidney, brain, liver, and pancreas.  Once the toxin binds to the receptor, the active subunit is internalized and shuts down the protein synthesis in the cells.  STEC infections are almost always foodborne in nature. The pathologic process is dependent on the production of the toxin. The most common alerting symptom of the infection is bloody diarrhea, however, non-bloody diarrhea can also be the presenting symptom… One of the most serious complications of STEC infections is Hemolytic Uremic Syndrome (HUS). However, this is not a common complication only affecting; 6-9% of STEC infected individuals; regardless, it has serious sequelae, and higher mortality. In HUS, 5-10 days after the onset of diarrhea, the patient develops a triad of acute renal failure, hemolytic anemia, and thrombocytopenia.

 

Useful For

  • Diagnosis of diarrheal disease caused by STEC
  • Diagnosis of HUS due to STECSTEC outbreak investigation

 

Testing Algorithm

  • Most diarrheal stools are submitted for stool culture, and STEC plate is a part of routine stool culture.
  • Bloody stool specimens tested initially for Clostridium difficile  are plated on a STEC plate and referred to PHML for Direct PCR testing for Stx
  • Positive STEC cultures are confirmed by PCR
  • All STEC isolates are referred to the National Microbiology Laboratory for typing, as a part of  a National surveillance program

 

Indications for Testing

  • Diarrhea, bloody diarrhea, HUS.

 

Method Name

Stool Culture. Shiga toxin testing

 

Reporting Name

Stool culture (STOOCU)

Shiga toxin PCR (SHTGP)

 

Aliases

Diarrhea,

Bloody diarrhea,

HUS

  • Stool specimen in Cary Blair medium or equivalent Transport medium. At room temperature the stool is acceptable for culture within an hour, which is not likely to be achieved, so it is always advised to submit the stool culture in an appropriate transport medium.
  • It is always recommended to obtain stool specimens prior to antimicrobial therapy to ensure microbial viability for better recovery of isolates

 

Specimen Minimum Volume
• At least one gram of stool collected in a proper transport medium

 

Transport Temperature

Specimen Room Temperature Refrigerated Frozen
Stool YES for one hour Yes for 24hr without transport medium and 48 hours with transport medium Yes for PCR only

Reject Due To
Mislabeled or unlabeled

 

Clinical history
Clinical information and in particular risk factors are necessary to triage testing and in the clinical interpretation of results
• Provide clinical history and suspected diagnosis
• Provide duration and descriptionof the diarrheal episode.
• Please state current antimicrobial therapy – dose, route of administration and start/end dates

Reference Values
• Stool is negative for shiga toxin producing E. Coli

 

Interpretation
Result interpretation should always be correlated with patient clinical history.. Positive STEC culture in a patient with diarrhea is usually considered a sufficient evidence for STEC infection, however the sensitivity of the PCR is higher. STEC agar plate can only grow viable bacteria, while PCR can detect both viable and nonviable organisms, thus it can be positive in convalescent stage or if the patient is treated with antimicrobials.. Discordant results should be carefully interpreted in consultation with the Microbiologist on call

 

Clinical Reference
• Rahal, E. A., Fadlallah, S. M., Nassar, F. J., Kazzi, N., & Matar, G. M. (2015). Approaches to treatment of emerging Shiga toxin-producing Escherichia coli infections highlighting the O104:H4 serotype. Frontiers in Cellular and Infection Microbiology, 5, 24. http://doi.org/10.3389/fcimb.2015.00024
• https://www.uptodate.com/contents/clinical-manifestations-diagnosis-and-treatment-of-enterohemorrhagic-escherichia-coli-ehec-infection?source=search_result&search=shiga%20toxin&selectedTitle=2~47
• Manual of Clinical Microbiology 9th edition
• https://www.cdc.gov/ecoli/general/

Status Days Analytic Time Maximum Laboratory Time Specimen Retention
Routine 24/7 Variable 5 days

14 days for typing

NA

 

 

Method Description
STEC testing by PCR and culture, followed by referral for typing

 

Performing Laboratory Location

Newfoundland & Labrador Public Health Laboratory
St. John’s

 
 

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