Escherichia Coli
Escherichia coli, or E. coli is a bacterium in the family Enterobacteriaceae that is found in the intestines of warm-blooded animals, including humans. E. coli represent about 0.1% of the total bacteria of an adult's intestines (on a Western diet). As part of the normal flora of the human intestinal tract, E. coli aids in food digestion by producing vitamin K and B-complex vitamins from undigested materials in the large intestine and suppresses the growth of harmful bacterial species. However, E. coli has also been linked to diseases in about every part of the body. Pathogenic strains of E. coli have been shown to cause pneumonia, urinary tract infections, wound and blood infections, and meningitis.
Toxin-producing strains of E. coli can cause severe gastroenteritis (hemorrhagic colitis), which can include abdominal pain, vomiting, and bloody diarrhea. In most people, the vomiting and diarrhea stop within two to three days. However, about 5–10% of the those affected will develop hemolytic-uremic syndrome (HUS), which is a rare condition that affects mostly children under the age of 10, but also may affect the elderly as well as persons with other illnesses. About 75% of HUS cases in the United States are caused by an enterohemorrhagic (intestinally-related organism that causes hemorrhaging) strain of E. coli referred to as E. coli O157:H7, while the remaining cases are caused by non-O157 strains. E. coli. O157:H7 is found in the intestinal tract of cattle. In the United States, the Centers for Disease Control and Prevention estimates that there are about 10,000–20,000 infections and 500 deaths annually that are caused by E. coli O157:H7.
E. coli O157:H7, first identified in 1982, and isolated with increasing frequency since then, is found in contaminated foods such as meat, dairy products, and juices. Symptoms of an E. coli O157:H7 infection start about seven days after infection with the bacteria. The first symptom is sudden onset of severe abdominal cramps. After a few hours, watery diarrhea begins, causing lose of fluids and electrolytes (dehydration), which causes the person to feel tired and ill. The watery diarrhea lasts for about a day, and then changes to bright red bloody stools, as the infection causes sores to form in the intestines. The bloody diarrhea lasts for two to five days, with as many as 10 bowel movements a day. Additional symptoms may include nausea and vomiting, without a fever, or with only a mild fever. After about five to 10 days, HUS can develop. HUS is characterized by destruction of red blood cells, damage to the lining of blood vessel walls, reduced urine production, and in severe cases, kidney failure. Toxins produced by the bacteria enter the blood stream, where they destroy red blood cells and platelets, which contribute to the clotting of blood. The damaged red blood cells and platelets clog tiny blood vessels in the kidneys, or cause lesions to form in the kidneys, making it difficult for the kidneys to remove wastes and extra fluid from the body, resulting in hypertension, fluid accumulation, and reduced production of urine. The diagnosis of an E. coli infection is made through a stool culture.
Treatment of HUS is supportive, with particular attention to management of fluids and electrolytes. Some studies have shown that the use of antibiotics and antimotility agents during an E. coli infection may worsen the course of the infection and should be avoided. Ninety percent of children with HUS who receive careful supportive care survive the initial acute stages of the condition, with most having no long-term effects. In about 50% of the cases, short term replacement of kidney function is required in the form of dialysis. However, between 10 and 30% of the survivors will have kidney damage that will lead to kidney failure immediately or within several years. These children with kidney failure require on-going dialysis to remove wastes and extra fluids from their bodies, or may require a kidney transplant.
The most common way an E. coli O157:H7 infection is contracted is through the consumption of undercooked ground beef (e.g., eating hamburgers that are still pink inside). Healthy cattle carry E. coli within their intestines. During the slaughtering process, the meat can become contaminated with the E. coli from the intestines. When contaminated beef is ground up, the E. coli bacteria are spread throughout the meat. Additional ways to contract an E. coli infection include drinking contaminated water and unpasteurized milk and juices, eating contaminated fruits and vegetables, and working with cattle. The infection is also easily transmitted from an infected person to others in settings such as day care centers and nursing homes when improper sanitary practices are used.
Prevention of HUS caused by ingestion of foods contaminated with E. coli O157:H7 and other toxin-producing bacteria is accomplished through practicing hygienic food preparation techniques, including adequate hand washing, cooking of meat thoroughly, defrosting meats safely, vigorous washing of fruits and vegetables, and handling leftovers properly. Irradiation of meat has been approved by the United States Food and Drug Administration and the United States Department of Agriculture in order to decrease bacterial contamination of consumer meat supplies.
The presence of E. coli in surface waters indicates that there has been fecal contamination of the water body from agricultural and/or urban and residential areas. However, the contribution from human vs. agricultural sources is difficult to determine. Since the concentration of E. coli in a surface water body is dependent on runoff from various sources of contamination, it is related to the land use and hydrology of the surrounding watershed. E. coli concentrations at a specific location in a water body will vary depending on the bacteria levels already in the water, inputs from various sources, dilution with precipitation and runoff, and die-off or multiplication of the organism within the water body. Sediments can act as a reservoir for E. coli, as the sediments protect the organisms from bacteriophages and microbial toxicants. The E. coli can persist in the sediments and contribute to concentrations in the overlying waters for months after the initial contamination.
Routine monitoring for enteropathogens, which cause gastrointestinal diseases and are a result of fecal contamination, is necessary to maintain water that is safe for drinking and swimming. Many of these organisms are hard to detect, so monitoring of an indicator organism is used to determine fecal contamination. To provide safe drinking water, the water is treated with chlorine, ultra-violet light, and/or ozone. Traditionally fecal coliform bacteria have been used as the indicator organisms for monitoring, but the test for these bacteria also detects thermotolerant non-fecal coliform bacteria.
Therefore, the U.S. Environmental Protection Agency (EPA) is recommending that E. coli as well as enterococci be used as indicators of fecal contamination of a water body instead of fecal coliform bacteria. The test for E. coli does not include non-fecal thermotolerant coliforms. An epidemiological study has shown that even though the strains of E. coli present in a water body may not be pathogenic, these organisms are the best predictor of swimmingassociated gastrointestinal illness.
The U.S. EPA recreational water quality standard is based on a threshold concentration of E. coli above which the health risk from waterborne disease is unacceptably high. The recommended standard corresponds to approximately 8 gastrointestinal illnesses per 1000 swimmers. The standard is based on two criteria: 1) a geometric mean of 126 organisms per 100 ml, based on several samples collected during dry weather conditions, or 2) 235 organisms/100 ml sample for any single water sample. During 2002, the U.S. EPA finalized guidance on the use of E. coli as the basis for bacterial water quality criteria to protect recreational freshwater bodies.
Resources
Books
Bell, Chris, and Alec Kyriakides. E. coli. Boca Raton: Chapman & Hall, 1998.
Burke, Brenda Lee. Don't Drink the Water: The Waterton Tragedy. Victoria, BC: Trafford Publishing, 2001.
Parry, Sharon, and S. Palmer. E. coli: Environmental Health Issues of Vtec 0157. London, UK:Spon Press, 2001.
Sussman, Max, ed. Escherichia coli: Mechanisms of Virulence. Cambridge, UK: Cambridge University Press, 1997.
U.S. Environmental Protection Agency. Implementation Guidance for Ambient Water Quality Criteria for Bacteria. Draft, EPA-823-B-02-003. Washington, DC: U.S. Environmental Protection Agency, 2002.
Periodicals
Koutkia, Polyxeni, Eleftherios Mylonakis, and Timothy Flanigan. "Enterohemorrhagic Escherichia coli: An Emerging Pathogen." American Family Physician, 56, no. 3 (September 1, 1997): 853–858.
Other
"Escherichia coli and Recreational Water Quality in Vermont." Bacterial Water Quality. February 7, 2000 [June 2002]. <http://snr.uvm.edu/www/pc/sal/e coli/index.htm>.
U.S. Food and Drug Administration. "Escherichia coli." Bad Bug Book. February 13, 2002 [cited May 25, 2002]. <http://vm.cfsan.fda.gov/~mow/ch ap15.html>.
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