Final answer:
The most common serotype of enterohemorrhagic E. coli (EHEC) is E. coli O157:H7, known for producing a Shiga-like toxin that can cause severe illnesses including hemorrhagic colitis and hemolytic uremic syndrome. This pathogenicity is due to genes for toxins acquired from Shigella dysenteriae. Identification of this strain is critical for preventing outbreaks and is done through PCR and serological typing.
Step-by-step explanation:
The most common serotype of enterohemorrhagic E. coli (EHEC) that is known to cause severe illnesses, including epidemics, is E. coli O157:H7. This strain possesses surface antigens, classified as O and H antigens, which contribute to its pathogenicity and the immune response it elicits. The 'O' refers to the O-side chain of the lipopolysaccharide and the 'H' to the flagella. Strain O157:H7 is infamous for producing a Shiga-like toxin responsible for severe conditions such as hemorrhagic colitis and hemolytic uremic syndrome, which could be life-threatening.
The pathogenic capabilities of EHEC O157:H7 are partly due to the acquisition of Shiga toxin genes through transduction, a form of horizontal gene transfer. These genes likely originated from Shigella dysenteriae and were integrated into the E. coli chromosome via a prophage from a bacteriophage that had previously infected Shigella. As this toxin halts protein synthesis within affected cells, it leads to cellular death and the disease manifestations associated with EHEC infections. Unlike enteropathogenic E. coli (EPEC) which lacks the Shiga toxin genes, EHEC harbors both genes necessary for pedestal formation on intestinal epithelial cells and the genes encoding for the Shiga-like toxin.
In the context of a potential outbreak or infection, distinguishing EPEC from EHEC is critical and achieved by testing for both the locus of enterocyte effacement (LEE) and the Shiga toxin genes. The Shiga-like toxin is also referred to as verotoxin due to its association with severe gastrointestinal disease. Surveillance methods such as PCR and serological typing are standard for identifying the presence of EHEC O157:H7, which is essential given this pathogen's potential to cause large-scale outbreaks through contaminated food and water.