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EHEC can cause disease ranging from relatively mild to life-threatening. Symptoms include bloody diarrhea with severe cramping, but no fever. Although it is often self-limiting, it can lead to hemorrhagic colitis and profuse bleeding. One possible complication is HUS. Diagnosis involves culture, often using MacConkey with sorbitol agar to differentiate between E. coli O157:H7, which does not ferment sorbitol, and other less virulent strains of E. coli that can ferment sorbitol.
Serological typing or PCR testing also can be used, as well as genetic testing for Shiga toxin. To distinguish EPEC from EHEC, because they both form pedestals on intestinal epithelial cells, it is necessary to test for genes encoding for both the Shiga-like toxin and for the LEE. Both EPEC and EHEC have LEE, but EPEC lacks the gene for Shiga toxin. Antibiotic therapy is not recommended and may worsen HUS because of the toxins released when the bacteria are killed, so supportive therapies must be used. [link] summarizes the characteristics of the four most common pathogenic groups.
| Some Pathogenic Groups of E. col i | ||||
|---|---|---|---|---|
| Group | Virulence Factors and Genes | Signs and Symptoms | Diagnostic Tests | Treatment |
| Enterotoxigenic E. coli (ETEC) | Heat stable enterotoxin similar to cholera toxin | Relatively mild, watery diarrhea | Culturing, PCR | Self-limiting; if needed, fluoroquinolones, doxycycline, rifaximin, TMP/SMZ; antibiotic resistance is a problem |
| Enteroinvasive E. coli (EIEC) | Inv (invasive plasmid) genes | Relatively mild, watery diarrhea; dysentery or inflammatory colitis may occur | Culturing, PCR; testing for inv gene; additional assays to distinguish from Shigella | Supportive therapy only; antibiotics not recommended |
| Enteropathogenic E. coli (EPEC) | Locus of enterocyte effacement (LEE) pathogenicity island | Severe fever, vomiting, nonbloody diarrhea, dehydration; potentially fatal | Culturing, PCR; detection of LEE lacking Shiga-like toxin genes | Self-limiting; if needed, fluoroquinolones, doxycycline, rifaximin (TMP/SMZ); antibiotic resistance is a problem |
| Enterohemorrhagic E. coli (EHEC) | Verotoxin | May be mild or very severe; bloody diarrhea; may result in HUS | Culturing; plate on MacConkey agar with sorbitol agar as it does not ferment sorbitol; PCR detection of LEE containing Shiga-like toxin genes | Antibiotics are not recommended due to the risk of HUS |
The gastrointestinal disease cholera is a serious infection often associated with poor sanitation, especially following natural disasters, because it is spread through contaminated water and food that has not been heated to temperatures high enough to kill the bacteria. It is caused by Vibrio cholerae serotype O1, a gram-negative, flagellated bacterium in the shape of a curved rod (vibrio). According to the CDC, cholera causes an estimated 3 to 5 million cases and 100,000 deaths each year. Centers for Disease Control and Prevention. Cholera—Vibrio cholerae Infection . Updated November 6, 2014. http://www.cdc.gov/cholera/general. Accessed Sept 14, 2016.
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