What is Escherichia coli O157:H7?
Escherichia coli O157:H7 is a serotype of enterohemorrhagic E. coli which is Shiga toxin-producing. It produces Shiga toxin 1 (Stx1) and/or Shiga toxin 2 (Stx2) as the virulence factors that contribute to its pathogenicity by the formation of attachment and effacing (A/E) lesions on human intestinal epithelium.
The minimum temperature for the E.coli O157:H7 to grow is about 8-10°C while the optimum temperature for the growth of E.coli O157:H7 is 37°C. At the maximum temperature of 44°C- 45°C, the growth of E.coli O157:H7 might be inhibited. It was also reported that E.coli O157:H7 is tolerant of acidic pH and this property enables them to develop the capability to survive in acidic foods such as fermented sausages, apple cider, and shredded hard salami.
Image Source: FDA
The genome of E. coli O157:H7
At the genomic level, the chromosomal size of E.coli O157:H7 is 5.5 megabases (Mb). Comparing the genome sequence of E.coli O157:H7 and E.coli K-12, the chromosome length of the E.coli O157:H7 is 869 kilobases (Kb) longer than that of E.coli K-12. Both E.coli O157:H7 and E.coli K-12 share a common 4.1Mb of highly conserved sequence (the backbone of the E.coli chromosome). The pathogenicity of E.coli O157:H7 is high, in which as little as 10 CFU (Colony Forming Unit) can cause an infection.
E.coli O157:H7 Outbreaks
In 1982, the outbreak of food-borne infections in Oregon and Michigan had brought the Shiga-toxin producing E.coli O157:H7 to be identified as a human pathogen. A case-control study about E.coli O157:H7 infection in Washington State had suggested that most of the E.coli O157:H7 outbreak is due to the problems occurred in meat processing and cooking process, with the result that showed that a high number of patients reported with E.coli O157:H7 infections had consumed regular hamburgers that were probably contaminated.
According to an article published by the Centers for Disease Control and Prevention (CDC) in 1999, it was estimated that E.coli O157:H7 infections cause 73,480 of illnesses, 2168 hospitalizations and 61 deaths in the United States. In this study, the number of foodborne infections was determined by the number of cases reported through passive surveillance systems such as the National Notifiable Disease Surveillance System and the Public Health Laboratory Information System.
During 2003-2012, the E.coli O157:H7 outbreaks in the United States had reduced to the number of 390, which included 4928 illnesses, 1272 hospitalizations, and 33 deaths. It was found that E.coli O157:H7 infections are underreported at a high degree due to several reasons such as the patients did not search for any medical care or no diagnostic test had been conducted to identify the illnesses suffered by the patients.
- bloody diarrhea/hemorrhagic colitis
- abdominal cramps
- hemolytic uremic syndrome
- thrombotic thrombocytopenic purpura
- renal failure
Mainly transmitted by foodborne through:
- consumption of contaminated foods
- undercooked meats
- contaminated water or raw milk
- contaminated vegetables due to the poor hygienic and agricultural practice of farms
Cattle are the most recognized reservoir for E.coli O157:H7 in many study and review paper. E.coli O157:H7 in the cattle feces can contaminate the water used by communities. The risk pathways of transmission also can be direct contact from animals to farm workers or from person to person.