Escherichia Coli (E-Coli) With Focus on O157:H7 Strain

Introduction and Historical Perspective

Escherichia coli (E. coli) is a group of bacteria that colonize the digestive tract of healthy animals and human beings. Most strains are harmless. The Escherichia coli O157: H7 (designated by its somatic, O, and flagella, H, antigens) was first discovered as a human pathogen during two outbreaks of hemorrhagic colitis in 1982. The first outbreak was in Oregon where there were 26 reported cases of which 19 were hospitalized. The second outbreak occurred in Michigan with 21 cases being reported and 14 being hospitalized. This occurred just three months after the first outbreak. The vehicle for this transmission was later traced back to undercooked hamburgers from a fast-food chain. The E. coli O157: H7 was later isolated from the patients ⁽⁶⁾.

Characteristics of Escherichia Coli: 0157: H7

E. coli O157:H7 is a virulent strain that produces a powerful toxin that sticks to the mucosa of the intestines where it causes extensive damages. The letter combination in its name represents the specific markers on its membrane; these markers differentiate it from other strains of E. coli. E. coli O157:H7 colonizes animal intestines. In cattle, it does not cause any form of the disease and therefore causes contamination of meat mostly at slaughterhouses during the process of slaughtering. The E. coli O157:H7 has the ability to produce large amounts of the virulent toxin known as Shiga toxin 1 and 2. It grows well in environments with minimum and maximum temperatures of 8^oC and 45^oC respectively. This strain is also more sensitive to heat than other strains of E. coli such as Salmonella. E. coli O157:H7 and is acid tolerant ^{(1, 4, 9)}.

Spreading of E. coli O157:H7

As earlier mentioned, this strain of E. coli is found in the intestines of healthy cattle and other herbivores. The process of slaughtering cattle in itself can lead to meat contamination as the organisms leave the intestines to other parts. The consumption of undercooked meat contaminated with E. coli O157:H7 can lead to serious infection. Those bacteria that colonize the cow’s udders or on ‘dirty’ equipment used in milk collection can get into raw milk and when this milk is consumed without being pasteurized can also lead to the spread of the infection. Other sources of E. coli O157:H7 infection may also include but are not limited to eating contaminated foods and water. Poor personal hygiene and handwashing habits have also been shown to be effective in the spread of bacteria from the stools of infected persons to other healthy people. This is very common in children whose caregivers/parents are not concerned with their toileting activities; this puts those they closely interact with at risk of being infected ⁽⁵⁾. A low infective dose of between 0.3 and 15 organisms per gram of food can cause infection. This dose was reported in the 1993 outbreak. Poor disposal of human waste in cases where the individuals are infected has also been shown to be a factor in the spread of E. coli O157:H7 infection. This is due to washing out of the waste downstream or into vegetable farms leading to contamination of vegetables and water for domestic use and drinking ⁽²⁾.

Pathophysiology

The pathophysiology of E. coli O157:H7 infection basically involves four main mechanisms namely: adherence to small-bowel mucosa, direct invasion of mucosal cells, and disruption of the microvillus brush border and toxin release. Once the bacteria are consumed together with the contaminated food, it reaches the intestines where it adheres to the intestinal mucosa. Once it has adhered, it produces a potent toxin that adheres to the walls of the mucosa causing severe destruction of the mucosa leading to bleeding and a lot of pain. The E. coli O157:H7 has an incubation period that ranges between 1 and 10 days (an average of 3 to 4 days). The destruction of the intestinal mucosal by the potent toxin leads to the development of hemorrhagic colitis that may further progress into hemolytic uremic syndrome (HUS). The destruction of the intestinal mucosa means that the normal physiologic function of the intestines is compromised as the surface area for absorption is greatly reduced ⁽²⁾. The release of the toxins marks the pick of the infections as this is when most of the symptoms are shown. Initially, the individual may even be asymptomatic.

Signs and Symptoms

Symptoms do start at about three to four days after exposure and can even last for several days. The victims of infection with bacteria normally develop acute bloody diarrhea which is accompanied by severe abdominal pains. It is worth noting that this infection can be asymptomatic with no bloody diarrhea. Nausea and vomiting do occur occasionally with or without low-grade fever. In pediatric patients, more so those under five years and the elderly, a complication such as hemolytic uremic syndrome (HUS) may develop and is characterized by red blood cell destruction and renal failure. Hemolytic uremic syndrome as a complication of infection by E. coli O157:H7 has far-reaching consequences that can lead to multiple organ failure ^{(7, 8)}. HUS is normally followed by acute onset of hemolytic anemia as a result of defragmentation of red blood cells, thrombocytopenia and acute renal failure. HUS may spread to other parts of the body affecting the central nervous system, pancreas, lung and heart. Two different studies carried out by Coad et al ⁽³⁾ and Fitzpatrick et al ⁽⁴⁾ showed that 95% of patients suffering from HUS do recover from the acute illness with zero chances of recurrence. These two studies also showed that prognosis in long-term cases is unclear with 15 – 40% of the survivors having renal sequelae. Another common complication is hemorrhagic colitis which is characterized by bloody diarrhea. It is the complications of E. coli O157:H7 infection that cause concern in that they normally lead to adverse effects ⁽²⁾. Other associated symptoms are those resulting from anemia as a result of blood loss and the destruction of red blood cells. These include pallor, fatigue, edema of the lower exterminates which may also be due to HUS, and weight loss.

Diagnosis

Diagnosis can be symptomatic whereby the physician notes the characteristic signs and symptoms. Another differential diagnosis may be the result of the symptoms but E. coli O157:H7 infection should be suspected. A stool culture can also be performed and it takes 3-5 days for results to be known. In the case of HUS, the following tests are performed; kidney function, blood clotting factors, and blood count. A study carried out by Chinyu et al ⁽²⁾ with the objective of reviewing the clinical relevance of E. coli O157:H7 infection had challenging results on the diagnosis of E. coli O157:H7 infection. They concluded that: “Infection with E. coli O157:H7 presents with many clinical manifestations and should be included in the differential diagnosis for any patient with new-onset bloody diarrhea. Development of the hemolytic-uremic syndrome or thrombotic thrombocytopenic purpura should raise strong suspicion of E. coli O157:H7 infection and should lead to prompt evaluation. If infection is confirmed, it should be reported to public health officials.”

Any person who presents with a history of bloody diarrhea should be suspected of having been infected with E. coli O157:H7. Although this is not the only factor in diagnosis, it directs the diagnosis process.

Treatment and Management

Most people infected with E. coli O157:H7 do recover without any specific treatment. Dehydration should be prevented by drinking a lot of oral fluids. In hemorrhagic uremic syndrome is normally treated through blood transfusion and kidney dialysis. Due to the severe nature of diarrhea, electrolyte and fluid replacement is one of the cornerstone therapies. A study carried out by Wong ⁽¹⁰⁾ showed that pediatric patients were at a greater risk of developing HUS as compared to those who were not treated. It is always advisable that physicians hold back antibiotics until the results of the stool culture are out; this also helps in ruling out other differential diagnoses. It is worth noting that currently there is no specific treatment for HUS. From the above, it is evident that supportive therapy is the only way out in helping the infected to recover quickly. Nutritional support also forms an integral part of the care given to those infected with E. coli O157:H7 as this will help in the quick recovery of the destroyed intestinal mucosa. Foods that may irritate the damaged mucosa should be avoided. The infected person should be on a light diet that is high in proteins and vitamins that are vital in the healing process of the damaged intestinal tissues ⁽⁶⁾. Treatment may also include treating the complications, for example, blood transfusion to replace the lost red blood cells and correct the anemia.

Preventive Measures

Currently, there are several interventions that have been put into place to control the prevalence of E. coli O157: H7. The food processing industry and specifically beef processing has put a number of food safety practices such as minimizing or total removal of fecal contamination during food production and processing. Thorough washing of hides before skinning cattle reduces contamination on the side of beef. Other measures include the use of FDA and USDA cleared antimicrobial such as Sanova and Inspexx in decontamination of the carcass. These two are known to reduce significantly microbial load on meat and other poultry products. Thermal pasteurization and steam vacuuming may be used in place of antimicrobial. Proper cooking practices especially in the cooking of meat have been shown to inactivate E. coli O157:H7. Proper personal hygiene and good hand washing practices are also very important when handling meat products. Good agricultural practices that prevent fecal contamination of farmland are essential. People involved in the food trade must ensure that they get their food supplies such as vegetables for raw consumption from sources that are accredited and ensure that the vegetables are safe for human consumption. During the preparation of raw vegetables for consumption, clean running tap water should be used to clean the vegetables before consumption. The public should be advised to discard outer leaves of vegetables such as lettuce and cabbage. Thorough washing should be done to do away with surface contamination ⁽¹¹⁾.

Conclusion

E. coli O157:H7 infection if not closely monitored can lead to major outbreaks. The technical part of it is its association to beef which most people ascribe to with consumption of poorly cooked ground beef. The factor that most hospitals do not carry out routine examination and screening for E. coli O157:H7 infection and tests are only carried at a physician’s request or when presenting symptoms are beyond a reasonable doubt.

Prevention of E coli O157: H7 infection is not easy due to the fact that the bacteria colonize intestines and of healthy cattle and other food animals. This strain is resistant to acidic conditions, high salt concentrations, and dehydration. The current public health policy on control and prevention of E. coli O157:H7 infection states that high levels of vigilance are needed to curb its spread, reduce food contamination, and ensure safe food practices ⁽¹¹⁾. This, therefore, leaves public health measures as the only way to contain the infections. Personal hygiene, food safety and sanitation, and proper cooking methods remain the core areas in the prevention and control of E. coli O157:H7 infection. Surveillance and monitoring activities by government agencies to ensure that all stakeholders abide by the laid down regulations and laws also helps in curbing the spread. Awareness campaigns and health promotion activities should be carried out with the main objective of educating the public on E. coli O157:H7 infection. Knowledge of E. coli O157:H7 infection will empower the public to take personal initiatives to prevent its spread. Above all, E. coli O157:H7 infection still remains a public health threat and more studies and clinical trials should be carried out in order to identify the best management practices ⁽¹¹⁾.

References

1. Buchanan, R. L., and Bagi, L. K. 1994. Expansion of response surface models for the growth of Escherichiacoli O157:H7 to include sodium nitrite as a variable. Intl. J. Food Microbiol 23: 317–322.
2. Chinyu, Su, M. D., and Lawrence, J. 1995. Escherichia coli O157: H7 Infection in Humans BMJ 123: 698-707
3. Coad, NAG, et al, 1991. Changes in the post-enteropathic form of the hemolytic uremic syndrome in children. Clin Nephrol 35: 10-16
4. Fitzpatrick, M. M., et al 1991. Long term renal outcome of childhood hemolytic uremic syndrome. BMJ 303: 489-492.
5. Jerolda, M. K., et al 2006. Long term renal outcome of childhood hemolytic uremic syndrome. Kenya Nursing Journal 5: 102-122.
6. Institute of Food Technologists’ Expert Panel on Food Safety and Nutrition. Food borne disease significance of Escherichia coli O157:H7 and other enterohemorrhagic E. coli.
7. Kleanthous, H., et al. 1990. Haemolytic uraemic syndromes in the British Isles, 1985-8: association with verocytotoxin producing Escherichia coli. Part 2: microbiological aspects. Arch Dis Child 65: 722-727
8. Milford, D. V., Taylor et al 1990. Haemolytic uraemic syndromes in the British Isles, 1985-8: association with verocytotoxin producing Escherichia coli. Part 1: clinical and epidemiological aspects. Arch Dis Child 65: 716-721
9. Rajkowski, K. T., and Marmer, B. S. 1995. Growth of Escherichiacoli O157:H7 at fluctuating incubation temperatures. Journal of Food Protect 58:1307–1313.
10. Wong C, Jelacic S, et al. 2000. The risk of hemolytic uremic syndrome after antibiotic treatment of Escherichia coli O157:H7 infections. N Engl J Med.
11. Jaguar, M. J., 2003. Community Health Nursing; Prevention of spread of E. coli. 4^th Edition. New Jersey: Pearson Education Inc.