E. coli O157:H7 Screening

E. coli O157:H7 is a gram-negative enteric bacteria that is a major foodborne pathogen. Healthy cattle are a reservoir of E. coli O157:H7. Consumption of E. coli O157:H7 contaminated food, especially undercooked ground meat, is the primary cause of this disease. E. coli O157:H7 can survive in the environment for more than a year. It can also be transmitted in water, unpasteurized milk, and other foods including turkey, mayonnaise, and cantaloupe. In addition, person-to-person transmission is a well-documented occurrence in households and day-care centers. 

E. coli O157:H7 infection is a major public health concern in North America, Europe, and other areas of the world. Although the total case numbers of E. coli O157:H7 infections are lower than those of other enteric pathogens such as Salmonella or Campylobacter spp., the diseases caused by E. coli O157:H7 showed much higher hospitalization and fatality rates

Most human cases begin with non-bloody diarrhea and some can resolve without further complication. However, E. coli O157:H7 produces Shiga toxin which can cause some patients to progress to bloody diarrhea and hemorrhagic colitis in 1 to 3 days. Between 5 and 10% of patients can develop hemolytic uremic syndrome (HUS). E. coli O157:H7 is the most common cause of HUS in the United States. Children and the elderly are at increased risk of developing HUS.

HUS is recognized by a triad of symptoms that includes reduced platelet count, fragmented erythrocytes, and renal failure. HUS is thought to be a toxemia, in which circulating bacterial lipopolysaccharide and Shiga-like toxins exert their combined influence on endothelial cells of specific organs, particularly the kidney.

 E. coli O157:H7 expresses somatic (O) antigen 157 and flagella (H) antigen 7. E. coli O157:H7 posesses unique features of delayed D-sorbitol fermentation (>24 h) and inability of producing β-glucuronidase, which can hydrolyze a synthetic molecule, 4-methyl-umbelliferyl-D-glucuronide (MUG). Thus, Sorbitol MacConkey (SMAC) agar supplemented with MUG has been used for detection of E. coli O157:H7. To increase the selectivity for E. coli O157:H7, cefixime, potassium tellurite, and vancomycin have been added to SMAC agar plates to inhibit other Gram-negative flora. The serotypes O157 and H7 can be further confirmed by latex agglutination assays.

References

Lim JY, Yoon J, Hovde CJ. A brief overview of Escherichia coli O157:H7 and its plasmid O157. J Microbiol Biotechnol. 2010 Jan;20(1):5-14.

Alhadlaq MA, et al. Overview of pathogenic Escherichia coli, with a focus on Shiga toxin-producing serotypes, global outbreaks (1982–2024) and food safety criteria, Gut Pathogens, 2024;16:1-18.