Enterohemorrhagic E. coli (EHEC)

Mechanism of EHEC Infection

The main virulence factor which makes HUS-inducing EHEC strains different from others is their ability to produce Shiga toxin. The two Shiga toxin variants exist as Stx1 and Stx2 where Stx2a and Stx2c subtypes show the strongest connection to HUS development. The AB5 toxin family includes Shiga toxins which bind to human cell glycosphingolipids such as globotriaosylceramide (Gb3) that exist on endothelial cells of glomeruli and brain tissue. The toxins block protein translation in host cells which results in cell death. The blood vessel damage and blood clot formation during HUS development occur because of these factors.

The consumption of EHEC-contaminated food items including undercooked meat and vegetables and fruits leads to bacterial colonization of the gut by the bacteria which then produces Shiga toxins. The bacterial genome of EHEC contains a prophage which functions as a viral DNA sequence integrated into its genetic material. The prophage exists in a dormant state during the lysogenic phase but becomes active when the bacterium faces environmental stressors such as antibiotic exposure which triggers the lytic cycle and Shiga toxin production. The toxins enter host cells through endocytosis after which they cause severe gastrointestinal symptoms including abdominal pain and bloody diarrhea.

Figure 1. Mechanism of enterohemorrhagic Escherichia coli (EHEC) infection and Shiga toxin production. (Strzelecki, 2025)

EHEC Laboratory Testing Methods

Cultural Techniques

• Sorbitol MacConkey Agar (sMac) detects E. coli O157 through its inability to ferment sorbitol but shows poor detection rates at 50-60%.
• The selective broth enrichment method helps to improve the recovery of E. coli O157.

Immunoassays

• The serotype-specific enzyme immunoassays show high sensitivity levels between 73-100% but they only detect E. coli O157.
• PCR Assays detect Shiga toxins and virulence factors with high sensitivity but these tests are not commonly used in laboratories.
• The cytotoxin testing method needs specialized tissue culture facilities yet it operates outside standard laboratory protocols.

EHEC continues to be a dangerous pathogen which causes severe health problems including bloody diarrhea and HUS. The management and prevention of EHEC infections require prompt detection through molecular and cultural and immunological testing methods. The development of CRISPR-Cas12/13 and microfluidic chip technologies will lead to faster and more accurate EHEC diagnostic methods that enhance medical results and public health reaction capabilities.