Understanding Escherichia coli Pathotypes

What are E. coli pathotypes and why are they important?

To better classify the diversity of E. coli, microbiologists developed the concept of pathotypes, which group strains that share similar virulence traits and cause similar diseases.^1,2,4,5 Pathotyping helps connect a strain's genetic makeup with its ability to cause disease. Different pathotypes possess distinct combinations of virulence factors, such as toxins, adhesins, invasins, and secretion systems, that determine how they interact with the host and the types of infections they cause. As a result, pathotype classification is widely used in clinical diagnostics, outbreak investigations, epidemiological surveillance, comparative genomics, and studies of bacterial evolution.

Broadly, pathogenic E. coli can be divided into two categories:

• Intestinal (diarrheagenic) pathotypes (DEC), which primarily cause gastrointestinal disease.
• Extraintestinal pathogenic E. coli (ExPEC), which cause infections outside the gastrointestinal tract, including urinary tract infections (UTIs), bloodstream infections, and neonatal meningitis.

Understanding the differences among pathotypes helps explain why some E. coli strains cause mild self-limiting diarrhea, while others can lead to severe complications such as hemolytic uremic syndrome (HUS), sepsis, or meningitis.^1,2

Table 1: E. coli pathotypes at a glance

How are E. coli pathotypes identified?

Historically, pathotypes were identified using serotyping, toxin detection, adherence assays, and animal models. Today, whole-genome sequencing (WGS) enables direct identification of virulence genes, allowing strains to be classified based on their pathogenic potential rather than phenotype alone.^1,2

Using genomes available through the ATCC Genome Portal and analyzed with EcoliTyper v1.2.1— a species-optimized genomic surveillance pipeline that integrates sequence type (ST) based on MLST, serotyping, phylogrouping and pathotype assignment—researchers can rapidly identify major diarrheagenic and extraintestinal pathogenic E. coli lineages.⁶ The ATCC Genome Portal connects genomic data directly to ATCC's authenticated biological materials, enabling researchers to quickly identify strains of interest and select reference organisms appropriate for diagnostic, epidemiological, or pathogenesis studies.

Highlights from the ATCC collection

Pathotyping of the ATCC E. coli collection identified representatives from nearly all major pathogenic E. coli lineages. Together, these strains provide a broad reference set for studying intestinal disease, extraintestinal infections, virulence evolution, and host-pathogen interactions.

Enterohemorrhagic E. coli (EHEC)

EHEC strains produce Shiga toxins and possess intestinal attachment mechanisms that contribute to severe foodborne disease, hemorrhagic colitis, and hemolytic uremic syndrome (HUS). EHEC is generally considered a subset of STEC that combines Shiga toxin production with additional adherence factors that enhance intestinal colonization. Important virulence determinants include Shiga toxins (stx1 and/or stx2) and the adhesin intimin (eae), which promotes attachment to intestinal epithelial cells.^1,2 The ATCC EHEC collection encompasses both classical O157:H7 strains and major non-O157 serotypes associated with foodborne outbreaks making them valuable reference organisms for studies of Shiga toxin-mediated disease, host-pathogen interactions, and food safety.

Table 2: Representative EHEC strains available from ATCC

Enteropathogenic E. coli (EPEC)

EPEC strains are defined by attaching-and-effacing lesions mediated by the locus of enterocyte effacement (LEE) pathogenicity island. They are important causes of infant and pediatric diarrheal disease worldwide.^1,2 These strains are useful models for studying epithelial attachment, pedestal formation, and the evolutionary relationship between EPEC and EHEC lineages. O26 non-stx lineages also provide insight into the evolution of Shiga toxin-producing pathogens.^1,2

Table 3: Representative EPEC strains available from ATCC

Enterotoxigenic E. coli (ETEC)

ETEC is a major cause of traveler’s diarrhea and childhood diarrheal disease, particularly in low- and middle-income countries. Disease results from production of heat-labile (LT) and/or heat-stable (ST) enterotoxins that disrupt normal intestinal fluid regulation.^1,2 These reference strains can be used in studies of enterotoxin biology, colonization factors, vaccine development, and host-pathogen interactions.

Table 4: Representative ETEC strains available from ATCC

Enteroaggregative E. coli (EAEC)

EAEC strains are characterized by aggregative adherence, biofilm formation, and prolonged colonization of the intestinal mucosa. They have been linked to persistent diarrhea, traveler’s diarrhea, and foodborne outbreaks.^1,3 The diversity of EAEC strains in the collection can support research into adherence mechanisms, biofilm formation, virulence regulation, and strain variation.

Table 5: Representative EAEC strains available from ATCC

Enteroinvasive E. coli (EIEC)

EIEC strains invade intestinal epithelial cells and share many pathogenic features with Shigella, causing inflammatory diarrhea and dysentery-like disease.^1,2 These strains support studies of intracellular invasion, epithelial interactions, and inflammatory intestinal disease.

Table 6: Representative EIEC strains available from ATCC

Diffusely adherent E. coli (DAEC)

DAEC strains display diffuse adherence patterns mediated primarily by Afa/Dr adhesins and have been associated with diarrheal disease and urinary tract colonization.^1,3 These isolates are useful for investigating bacterial attachment, host-cell signaling, and adhesin-mediated pathogenesis.

Table 7: Representative DAEC strains available from ATCC

Shiga toxin-producing E. coli (STEC)

STEC strains produce Shiga toxins but may lack some of the adherence factors commonly associated with EHEC. They remain important foodborne pathogens capable of causing severe disease.^1,2 These isolates allow researchers to examine Shiga toxin biology independently of classical EHEC-associated mechanisms.

Table 8: Representative STEC strains available from ATCC

Hybrid pathotypes (STEC-EAEC hybrid)

Genome-based pathotyping has revealed the presence of hybrid pathogens formed through horizontal gene transfer between distinct E. coli lineages. These combinations of virulence factors can produce strains with increased pathogenic potential.^1,4 ATCC® BAA-2326™ and BAA-3235™ belong to the O104:H4 lineage associated with the 2011 Germany outbreak and contain virulence characteristics from both STEC and EAEC. These strains provide models for studying pathogen emergence, horizontal gene transfer, and virulence evolution.

Extraintestinal pathogenic E. coli (ExPEC)

Not all pathogenic E. coli strains cause intestinal disease. Extraintestinal pathogenic E. coli (ExPEC) are responsible for urinary tract infections, neonatal meningitis, sepsis, and bloodstream infections. Unlike diarrheagenic E. coli pathotypes, ExPEC strains are defined by combinations of adhesins, toxins, iron acquisition systems, capsules, and fitness factors rather than a small group of defining virulence genes.^4,5 These strains can support research on urinary tract infection pathogenesis, neonatal meningitis, host adaptation, antimicrobial resistance, and invasive disease.^4,5

Table 9: Representative ExPEC strains available from ATCC

Advancing research with ATCC reference strains

The ATCC E. coli collection provides researchers with a diverse, authenticated, and genomically characterized resource representing both intestinal and extraintestinal pathogenic lineages. Each strain is maintained under rigorous quality control to ensure authenticity, purity, and traceability. Standardized characterization data and associated genomic information are available through the ATCC product page and its respective Genome Portal page, supporting reproducible research. From classical EHEC outbreak strains to UPEC and MNEC reference isolates, the collection supports comparative genomics, virulence research, antimicrobial resistance studies, assay development, food safety testing, and public health applications.

Understanding E. coli pathotypes is increasingly important as whole-genome sequencing reveals the extensive diversity within the species. The differences between strains can translate into dramatically different virulence mechanisms, transmission dynamics, and clinical outcomes. By classifying isolates according to pathotype, researchers gain a framework for connecting genomic variation with disease biology.^1,4

Integrating comprehensive genomic characterization with authenticated biological materials enables researchers to move beyond species-level identification and toward a deeper understanding of the specific genetic factors that drive pathogenicity. As new virulence mechanisms and hybrid lineages continue to emerge, resources such as the ATCC collection and its Genome Portal will remain essential for advancing translational research, improving diagnostics, supporting public health surveillance, and enabling the development of next-generation therapeutics and vaccines.^1,4,6

Did you know?

ATCC provides the whole-genome sequences for over 250 Escherichia coli strains on the ATCC Genome Portal.

Explore now

References

1. Robins-Browne RM, et al. Are Escherichia coli Pathotypes Still Relevant in the Era of Whole-Genome Sequencing? Front Cell Infect Microbiol 6: 141, 2016. PubMed: 27917373
2. Kaper JB, Nataro JP, Mobley HLT. Pathogenic Escherichia coli. Nat Rev Microbiol 2(2): 123-140, 2004. PubMed: 15040260
3. Clements A, et al. Infection Strategies of Enteric Pathogenic Escherichia coli. Gut Microbes  3(2): 71-87, 2012. PubMed: 22555463
4. Geurtsen J, et al. Genomics and Pathotypes of the Many Faces of Escherichia coli. FEMS Microbiol Rev 46(6): fuac031, 2022. PubMed: 35749579
5. Whelan S, Lucey B, Finn K. Uropathogenic Escherichia coli (UPEC)-Associated Urinary Tract Infections: The Molecular Basis for Challenges to Effective Treatment. Microorganisms  11(9): 2169, 2023. PubMed: 37764013
6. Beckley B, Vincent A. EcoliTyper: a Species-Optimized Computational Pipeline for Comprehensive Genotyping and Surveillance of Escherichia coli. BMC Bioinformatics DOI: 10.1186/s12859-026-06529-6, 2026. PubMed: 42265598