Escherichia coli O157:H7 Overview

Overview

Introduction to Escherichia. coli O157:H7

The Shiga toxin-producing E. coli (STEC) serotype E. coli O157:H7 produces Stx1 and/or Stx2 (mainly Stx2 subtypes) and contains the locus of enterocyte effacement (LEE) pathogenicity island which causes attaching-and-effacing lesions and fails to ferment sorbitol (resulting in colorless colonies on SMAC agar). The infectious dose of this pathogen requires fewer than 100 CFU to cause infection.

The infection causes hemorrhagic colitis which results in severe abdominal pain and extensive bloody stools without substantial fever development. The development of hemolytic uremic syndrome (HUS) occurs in 5-15% of cases primarily affecting children under ten years and elderly patients who develop the triad of microangiopathic hemolytic anemia and thrombocytopenia and acute kidney injury. The condition of HUS stands as the primary reason for pediatric acute renal failure throughout various nations while resulting in 5% patient deaths and resulting in permanent kidney damage for many survivors.

The main habitat of this bacteria exists in cattle but human transmission happens through consuming raw milk and undercooked beef and through contact with contaminated produce and water and by direct person-to-person transmission. The use of antibiotics leads to higher HUS risk because it stimulates toxin production so patients receive only supportive care. The prevention of this infection depends on proper food preparation at 71°C or higher and milk pasteurization and produce cleaning and proper hand hygiene practices.

Key Characteristics of E. coli O157:H7

Serotype: The bacterium contains the O157:H7 serotype which identifies its somatic antigen 157 and flagellar antigen 7
Shiga toxins: The bacteria produce two primary toxins known as Stx1 and Stx2 but Stx2 toxin leads to severe disease symptoms.
Does NOT ferment sorbitol: The bacterium fails to ferment sorbitol which results in a colorless appearance on Sorbitol-MacConkey agar (SMAC) tests thus enabling diagnostic identification (most E. coli strains ferment sorbitol to produce pink results).
Carries the locus of enterocyte effacement (LEE): The pathogenicity island known as locus of enterocyte effacement (LEE) enables the bacteria to create attaching-and-effacing (A/E) lesions on intestinal cells.
Low infectious dose: The pathogen requires only 100 organisms to start causing illness.

Figure 1. Summary of E. coli O157:H7 pathogenesis using basic symbols. (Source: Gally, 2017)

E. coli O157:H7 Genome and Major Virulence Factors

The E. coli O157:H7 genome contains 5.5 Mb of DNA which includes a 4.1 Mb chromosome and a 90 kb virulence plasmid named pO157. The genome of E. coli O157:H7 contains 1.4 Mb of unique DNA sequences which stem from horizontal gene transfer through phage-mediated processes.

Major virulence factors:

Shiga toxins (Stx1, Stx2 & variants): The pathogen contains Shiga toxins Stx1 and Stx2 and their variants which stem from lambdoid prophages that carry stx1/stx2 genes. The Stx2 toxin variant shows the strongest link to severe disease progression and HUS development. The toxin functions by blocking protein synthesis through ribosomal damage which results in endothelial tissue destruction.
Locus of enterocyte effacement (LEE): The Locus of enterocyte effacement (LEE) contains a 35–43 kb pathogenicity island which includes a Type III secretion system (T3SS) and genes for intimin (eae) and translocated intimin receptor (Tir) and effectors (Esp). The pathogen creates A/E lesions through its LEE system which leads to pedestal formation.
pO157 plasmid: The pO157 plasmid contains three main virulence genes which include enterohemolysin (ehxA) and catalase-peroxidase (katP) and serine protease (espP) and toxB adhesion-related genes.
Other factors: The pathogen contains additional virulence factors which include Non-LEE encoded effectors (Nle) and O-antigen and H7 flagellar genes that help the bacteria resist serum components and evade the host immune system.

Host Range of E. coli O157:H7

E. coli O157:H7 demonstrates exceptional adaptability which enables it to thrive in cattle while causing severe disease in human hosts. The pathogen uses LEE-mediated attaching-effacing mechanisms together with flagella and curli fimbriae and EspA filaments to establish efficient colonization of the bovine recto-anal junction which results in prolonged high-level fecal shedding without causing any clinical symptoms in the primary host. The pathogen survives in external environments and human infections through multiple stress-resistance systems which include glutamate- and glutamine- and arginine-dependent acid resistance and RpoS-regulated responses for gastric pH 2–3 survival and tellurite resistance and enhanced oxidative stress tolerance and low-temperature survival and osmotic tolerance and robust biofilm formation on produce and meat and abiotic surfaces. The pathogen maintains efficient transmission from cattle to humans through its ability to withstand food processing and refrigeration and acidic foods and human stomach conditions.

E. coli O157:H7 Detection Technologies

The detection of E. coli O157:H7 requires immediate and precise methods because it affects food safety and medical diagnosis and outbreak tracing. The detection of E. coli O157:H7 uses multiple methods which include culture-based techniques and immunological tests and molecular assays and new detection approaches.

Culture-based (gold standard): The detection of E. coli O157:H7 relies on Sorbitol-MacConkey agar (SMAC) or CT-SMAC (with cefixime-tellurite) for culture-based identification which produces non-sorbitol-fermenting colorless colonies that need O157 latex agglutination and H7 flagellar confirmation.
Immunological: The detection of E. coli O157:H7 uses lateral flow immunoassays and ELISA tests which identify Stx1/Stx2 or O157 antigen. The detection time for these methods ranges from 15 to 30 minutes although they show reduced sensitivity when compared to molecular detection methods.
Molecular (current clinical and reference standard): The current clinical and reference standard for E. coli O157 detection uses real-time PCR to detect stx1/stx2 and eae and O157-specific genes.
Isothermal amplification: The detection methods of isothermal amplification include Loop-mediated isothermal amplification (LAMP) and recombinase polymerase amplification (RPA) which allow for field-based equipment-independent testing.
Whole-genome sequencing (WGS): Whole-genome sequencing (WGS) serves as a reference laboratory tool for PulseNet to perform high-resolution strain typing and outbreak investigation.

Emerging technologies: The detection methods of CRISPR-Cas12/13-based SHERLOCK and biosensors and MALDI-TOF MS for rapid colony confirmation and metagenomic shotgun sequencing from enriched food samples represent new technologies.

Figure 2. Schematic illustration of the preparation and use of foam-based sandwich ELISA (f-ELISA). (a) Immobilization of antibodies and capture of E coli O157:H7. (b) Addition of HRP-labeled secondary antibody and enzymatic substrate TMB to generate color signals and obtaining of images using a smartphone. (Source: Pan, 2024)

Creative Diagnostics Solutions for O157:H7 Detection

Creative Diagnostics provides a wide range of high-quality reagents and antibodies and ready-to-use kits for E. coli O157 detection which serves both industrial food testing and research applications and diagnostic development. The company provides O157 LPS and H7 flagellin and Shiga toxin components and specific monoclonal and polyclonal antibodies for ELISA and LFIA and Western blot applications and ELISA kits for food and water analysis. Creative Diagnostics provides materials for lateral flow assay development through their nitrocellulose membranes and gold nanoparticle conjugates and detector reagents and optimized buffers. The company provides complete development services and OEM solutions which include assay optimization and antibody conjugation and diagnostic kit prototyping and scalable manufacturing solutions to help partners create high-performance detection platforms that meet regulatory standards.

High-Quality Antigens and Proteins

Specific Monoclonal and Polyclonal Antibodies

These antibodies are suitable for ELISA, LFIA, Western blot, and other immunoassay platforms.

Ready-to-Use Detection Kits

Creative Diagnostics supports partners across the food industry, contract testing laboratories, and diagnostic developers in building high-performance, regulatory-ready detection solutions for E. coli O157:H7.

Related Resources

Shiga Toxin-Producing E. coli (STEC/VTEC)

Shiga Toxin 1 vs Shiga Toxin 2

References

Gally, David L., and Mark P. Stevens. "Microbe Profile: Escherichia coli O157: H7–notorious relative of the microbiologist's workhorse." Microbiology 163, no. 1 (2017): 1-3.
Pan, Bofeng, et al. "Rapid and ultrasensitive colorimetric biosensors for onsite detection of Escherichia coli O157: H7 in fluids." ACS sensors 9.2 (2024): 912-922.

Reagent Solutions

E. coli O157 H7 Antibodies

Target	Cat. No.	Product Name	Host	Isotype	Application
E. coli Flagellin	DMAB-CAB5124	Human Anti-E. coli O157:H7 FliC Monoclonal antibody, clone B1475	Human	IgG1		Inquiry
E. coli O Antigen	DPAB0438	Goat Anti-E.coli O157:H7 polyclonal antibody	Goat	IgG	ELISA	Inquiry

E. coli O157 H7 Antigens

Target	Cat. No.	Product Name	Host
E. coli Verotoxin	DAGA-985	Recombinant E.Coli O157:H7 Shiga Like Toxin-2 Subunit B [His]	E. coli	Inquiry
E. coli LPS	DAGB132	E. coli O157:H7 LPS	E. coli	Inquiry
E. coli	DAG-ZL0474	Inactivated Escherichia coli O157:H7 Culture Fluid	N/A	Inquiry
	DAG-ZL0479	Inactivated Escherichia coli EHEC O157:H7 Culture Fluid	N/A	Inquiry
	DAG-ZL0493	Inactivated Escherichia coli O157:H7 Culture Fluid	N/A	Inquiry

E. coli O157 ELISA Kits

Target	Cat. No.	Product Name	Size	Species	Application	Detection Sample
E. coli O Antigen	DEIA-NS2402-6	E.coli O157 ELISA Kit	96T	Human	Quantitative	Ground beef, milk, lettuce, etc	Inquiry
E. coli	DEIA2437	E. coli O157 ELISA Kit	96T	N/A	Quantitative	Food, Fecal or Environmental Samples	Inquiry

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