Escherichia coli O157:H7

Escherichia coli O157:H7 is a serotype of the bacterial species Escherichia coli and is one of the Shiga-like toxin–producing types of E. coli. It is a cause of disease, typically foodborne illness, through consumption of contaminated and raw food, including raw milk and undercooked ground beef.^[1][2] Infection with this type of pathogenic bacteria may lead to hemorrhagic diarrhea, and to kidney failure; these have been reported to cause the deaths of children younger than five years of age, of elderly patients, and of patients whose immune systems are otherwise compromised.

Transmission is via the fecal–oral route, and most illness has been through distribution of contaminated raw leaf green vegetables, undercooked meat and raw milk.^[3]

Signs and symptoms

E. coli O157:H7 infection often causes severe, acute hemorrhagic diarrhea (although nonhemorrhagic diarrhea is also possible) and abdominal

Like the other strains of the E. coli, O157:H7 is gram-negative and oxidase-negative. Unlike many other strains, it does not ferment sorbitol, which provides a basis for clinical laboratory differentiation of the strain. Strains of E. coli that express Shiga and Shiga-like toxins gained that ability via infection with a prophage containing the structural gene coding for the toxin, and nonproducing strains may become infected and produce shiga-like toxins after incubation with shiga toxin positive strains. The prophage responsible seems to have infected the strain's ancestors fairly recently, as viral particles have been observed to replicate in the host if it is stressed in some way (e.g. antibiotics).^[6][7]

All clinical isolates of E. coli O157:H7 possess the plasmid pO157.^[8] The periplasmic catalase is encoded on pO157 and may enhance the virulence of the bacterium by providing additional oxidative protection when infecting the host.^[9] E. coli O157:H7 non-hemorrhagic strains are converted to hemorrhagic strains by lysogenic conversion after bacteriophage infection of non-hemorrhagic cells.^{[citation needed]}

Natural habitat

While it is relatively uncommon, the E. coli serotype O157:H7 can naturally be found in the intestinal contents of some cattle, goats, and even sheep.^{[citation needed]} The digestive tract of cattle lack the Shiga toxin receptor globotriaosylceramide, and thus, these can be asymptomatic carriers of the bacterium.^[10] The prevalence of E. coli O157:H7 in North American feedlot cattle herds ranges from 0 to 60%.^[11] Some cattle may also be so-called "super-shedders" of the bacterium. Super-shedders may be defined as cattle exhibiting rectoanal junction colonization and excreting >10^{3 to 4} CFU g⁻¹ feces. Super-shedders have been found to constitute a small proportion of the cattle in a feedlot (<10%) but they may account for >90% of all E. coli O157:H7 excreted.^[12]

Transmission

Infection with E. coli O157:H7 can come from ingestion of contaminated food or water, or oral contact with contaminated surfaces. Examples of this can be undercooked ground beef but also leafy vegetables and raw milk. Fields often become contaminated with the bacterium through irrigation processes or contaminated water naturally entering the soil.

Avoiding the consumption of, or contact with, unpasteurized dairy products, undercooked beef, uncleaned vegetables, and non disinfected water reduces the risk of an E. coli infection. Proper hand washing with water that has been treated with adequate levels of chlorine or other effective disinfectants after using the lavatory or changing a diaper, especially among children or those with diarrhea, reduces the risk of transmission.^[17][18]

Surveillance

E. coli O157:H7 infection is a nationally

While fluid replacement and blood pressure support may be necessary to prevent death from dehydration, most patients recover without treatment in 5–10 days. There is no evidence that antibiotics improve the course of disease, and treatment with antibiotics may precipitate hemolytic–uremic syndrome (HUS).^[20] The antibiotics are thought to trigger prophage induction, and the prophages released by the dying bacteria infect other susceptible bacteria, converting them into toxin-producing forms. Antidiarrheal agents, such as loperamide (imodium), should also be avoided as they may prolong the duration of the infection.^{[citation needed]}

Certain novel treatment strategies, such as the use of anti-induction strategies to prevent toxin production^[21] and the use of anti-Shiga toxin antibodies,^[22] have also been proposed.

History

The first recorded observation of E. coli O157:H7 was in 1975, in association with a sporadic case of

The United States Department of Agriculture banned the sale of ground beef contaminated with the O157:H7 strain in 1994.^[26]

Culture and society

Costs

The pathogen results in an estimated 2,100 hospitalizations annually in the United States. The illness is often misdiagnosed; therefore, expensive and invasive diagnostic procedures may be performed. Patients who develop HUS often require prolonged hospitalization, dialysis, and long-term followup.^[27]

See also

• 1993 Jack in the Box E. coli outbreak
• 1996 Odwalla E. coli outbreak
• 2011 Germany E. coli O104:H4 outbreak
• Escherichia coli O104:H4
• Escherichia coli O121
• Food-induced purpura
• List of foodborne illness outbreaks
• Walkerton E. coli outbreak

References