Detection of Enterovirulent Escherichia Coli

By: Jvo Siegrist, AnalytiX Volume 8 Article 4

Enterovirulent E. coli, like the enterohemorrhagic E. coli (EHEC), are known to cause severe disease. Undercooked or raw meat is often responsible for outbreaks. One solution is to detect their presence in food with new and reliable growth media.

Jvo Siegrist, Product Manager Microbiology ivo.siegrist@sial.com

E. coli are Gram-negative, rod-shaped bacteria belonging to the family of Enterobacteriaceae. Normally a useful organism in the human digestive system, a few E. coli strains are capable of causing human illness by several different mechanisms. The enterohemorrhagic E. coli (EHEC) strain designated as E. coli O157:H7 is the most important of the enterovirulent E. coli. It produces large quantities of one or more potent toxins that cause severe hemorrhagic colitis or hemolytic uremic syndrome. These toxins (verotoxin, shiga-like toxin) are identical or closely related to the toxin produced by Shigella dysenteriae.

Different types of E. coli are known based on their pathogenic mechanisms:

  • Enteropathogenic E. coli (EPEC). Virulence mechanism is unrelated to the excretion of typical E. coli enterotoxins. Causes gastroenteritis (childhood diarrhea).
  • Enteroinvasive E. coli (EIEC) or Shiga toxin-producing E. coli (STEC). Causes a Shigella-like dysentery.
  • Enterotoxigenic E. coli (ETEC). Produce heat-labile (LT) or heat-stable (ST) enterotoxins. Cause traveller’s diarrhea.
  • Enteroaggregative E. coli (EAggEC) or Enteroadherent E. coli (EAEC). Able to attach to tissue culture cells in an aggregative manner and may produce EAST (EnteroAggregative ST) toxin. Subgroups, like diffusely adhering E. coli (DAEC) strains and Cytodetaching E. coli (CDEC), are differentiated. Primarily associated with persistent diarrhea in children in developing countries and also traveller’s diarrhea

 

Important features used for the detection of E. coli O157:H7 from other E. coli and other bacteria appear in Table 1. These features are also used in our diverse media to detect and differentiate E. coli O157:H7 found in Table 2.

 


Table 1 Biochemical characteristics of E. coli O157:H7

 

Media System Part No. Name Description
Non-selective + differential system 17178 Mucate Broth For the identification of enteropathogenic E. coli and Shigella species in milk and milk products.
Selective + differential systems 44782 E. coli O157:H7 MUG Agar A fluorescent selective agar for the isolation and differentiation of enterohaemorrhagic (EHEC) E. coli O157:H7-strains from food and clinical material.
  39894 HiCrome™ EC O157 Agar
Optional supplement: 0.25 mL/L 1 % potassium tellurite solution (17774)
A chromogenic medium for isolation and differentiation of E. coli O157 from food and environmental samples.
  72557 HiCrome™ EC O157:H7 Selective Agar, Base
Supplement: 1 vial/L of HiCrome ECO157:H7 Selective Supplement (44931)
Recommended for selective isolation and easy detection of E. coli O157:H7 from food samples.
  80330 HiCrome™ Enrichment Broth Base for EC O157:H7 Recommended for isolation and selective differentiation of E. coli 0157:H7 from food and environmental samples by a chromogenic method.
  83339 HiCrome™ MacConkey-Sorbitol Agar
Supplement: 2 vial/L Tellurite- Cefixime Supplement (77981)
Recommended for selective isolation of E. coli O157:H7 from food and animal feed. The medium contains sorbitol instead of lactose. E. coli produce purple colonies. The colour is due to production of acid from sorbitol and the neutral red indicator and the B.C. indicator, which detects the presence of the enzyme β-D-glucuronidase, specific for E. coli. Enteropathogenic strains of E. coli O157 do not possess β-D-glucuronidase activity and do not ferment sorbitol, producing colourless colonies.
  88902 MacConkey-Sorbitol Agar Optional supplement: 2 vial/L CTSupplement (77981) Recommended medium for selective isolation of pathogenic E. coli O157:H7 which ferments sorbitol but not lactose.
Selective media 71882 mEC Broth with Novobiocin For the selective enrichment of enterohemorrhagic E. coli in food. The medium is used for the isolation and identification of E. coli O157:H7 from meat according to USDA-FSIS methods.
  76704 mTSB Broth with Novobiocincin For the selective enrichment of enterohemorrhagic E. coli in food. The medium meets the requirements of the DIN Norm 10167 for the detection of E. coli serotype O157:H7 in food. It is also recommended by the FDA-BAM as a method for the isolation of enterohemorrhagic E. coli.

 

Table 2 List of Sigma-Aldrich media for enterovirulent E. coli

Key: red = chromogenic media; blue = fluorescent media

For a complete list of our growth and selective media, and our other products and resources for microbiology, please visit our website sigma-aldrich.com/microbiology

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Materials