Pathogenic E. coli: Types, Toxins, and Detection Methods

Escherichia coli (E. coli) exists as a large collection of non-spore-forming gram-negative bacteria which are motile through peritrichous flagella and mostly exist without causing harm to humans. The bacterium exists as a non-sporulated Gram-negative bacillus which reaches dimensions of 1 μm in length and 0.35 μm in width but its size changes based on strain type and environmental conditionsylum and belongs to the Enterobacteriaceae family. The human gut contains E. coli bacteria aerobic and anaerobic conditions. The bacterium E. coli exists within the Proteobacteria ph. The bacterium exists as an oxidase-negative facultative anaerobe which thrives under both which make up only 0.1 to 5% of its total microbial population. The gastrointestinal tracts of humans and animals normally host E. coli strains which exist as harmless members of their normal microbial communities. Certain E. coli strains developed pathogenic characteristics through the acquisition of virulence factors from plasmids and transposons and bacteriophages and pathogenicity elements. The pathogenic E. coli strains receive their classification through serogroup analysis and pathogenicity mechanisms and clinical symptoms and virulence factor identification. DEC represent the leading bacterial pathogens worldwide which cause significant illness and death in developing nations. The five main phylogenetic groups of E. coli consist of A (blue), B1 (green), B2 (brown), D (pink) and E (red). The specific pathotype Shigella/EIEC has additional phylogroups which are shown in black. The hybrid EAEC and STEC strains show representation through both open square and open circle symbols. The unmarked strains consist of commensal bacteria and ExPEC.

Figure 1. Phylogenetic tree of enteric/diarrheagenic E. coli (DEC). (Roussel, 2019)

Key Virulence Factors and Toxins

The virulence factors of E. coli exist on mobile genetic elements and plasmids and pathogenicity islands which produce endotoxins and exotoxins and adhesion and invasion and iron acquisition factors. The virulence factors of IPEC include verocytotoxin1, verocytotoxin 2, intimin, heat-stable enterotoxin, human variant, porcine variant, heat labile enterotoxin, and invasive plasmid antigen. The pathogenicity of Escherichia coli depends on multiple virulence factors which help the bacteria establish colonization and produce toxins and invade host cells.

Table 1. Gene target, primer sequence, and amplicon size for common intestinal pathogenic E. coli virulence factors

Virulence Factors and Toxins/Toxin Receptor Antibodies

Virulence Factors and Toxins Antigens