Escherichia Coli Essay, Research Paper

Biology

Escherichia coli

Escherichia coli

Escherichia coli is an Enterobactericeae bacteria. This family name is derived from the fact that nearly all species in it, more or less, constantly inhabit the intestines of humans and animals. Because of its widespread presence in the environment and its ability to promote disease in humans, one of the most prominent members of this family is the species Escherichia coli. This bacterium is so common that its name has come to describe all similar bacteria as coliform or coli-like.

These enterobacteria are gram-negative, nonspore-forming straight rods, aerobic and facultative anaerobes, ranging from 1 to 2 mm in diameter and are from 3 to 10 mm in length. All species ferment glucose, which allows for a testing method known as presumptive E. coli, and all microscopically, are indistinguishable. Most species are motile with nonpolar flagellae. They have been classified by a system developed in part by Edwards and Ewing, and Escherichia was named after a German scientist named Escherich. Enterobactericeae is subdivided into five tribes, Escherichieae being one of them.

E. coli occurs in enormous numbers in normal feces and is widely distributed in the intestinal canal of animals and humans. Ordinarily, it does no harm. Various species of E. coli are of special importance to medical and sanitation personnel because certain serotypes cause intestinal and urinary tract infections and are transmitted in water and milk. E. coli is very similar to Salmonella and Shigella bacteria and can only be distinguished during biochemical tests in a laboratory.

E. coli is present in health people and animals, and actually aids in the digestive processes. The majority of E. coli in the intestinal tract are not disease-causing to the host organism, but if by chance the bacteria enter the urinary tract or any other part of the host, disease occurs. Methods of contamination could include inadequate hand-washing after using the toilet, drinking contaminated water or milk, eating undercooked contaminated meat, unsterile medical procedures, and perforation of the intestines due to accident or another trauma. Normal disease symptoms include traveler s diarrhea, vomiting, cramping, and dehydration.

Since E. coli is always present in feces, and since other species of the Escherichieae tribe frequently accompany and closely resemble it, this tribe is frequently referred to as the coliform group. The presence of any of them in water, milk, or food in considerable numbers strongly suggests pollution with sewage and feces. These bacteria are easily cultured and recognized, usually remaining alive in food and water for long periods of time. The coliform group is the indicator species in bacteriologic examinations of water, milk and food as evidence of fecal pollution and potential infection.

Sewage pollution can introduce a variety of other diseases, such as viruses, protozoa, and other harmful bacteria, but E. coli is most predominant and easiest to identify.

A new development in the history of coliform diseases came in 1982, when a strain of E. coli labeled as 0157:H7 was identified as a human pathogen. Clusters of disease outbreaks have occurred across the United States since then, the most famous of which was the Jack in the Box incident in 1993 in the state of Washington, resulting in four deaths and 176 hospitalizations. The Centers for Disease Control have established that undercooked beef hamburgers were the cause of the outbreak. Since that time, many more clusters have been reported.

Cattle are the only mammals that carry the O157:H7 serotype. It is spread during the slaughtering processing, when the intestines are ruptured by accident, spilling the contents and E coli onto the meat. The CDC estimates that approximately 1% of American cattle are contaminated.

People most likely to have a severe reaction to these bacteria are those who are very young, very old, or have a compromised immune system because of another disease. Daycare centers, nursing homes, and hospitals have the potential for severe outbreaks, primarily because of transmission during diaper-changing with contaminated hands, and hand-mouth transmission in young children.

The body temperature of a healthy human is the ideal temperature for E. coli O157:H7. Once it is ingested, it quickly begins to multiply and there is little to stop it and treatment is limited. The symptom that distinguishes E. coli O157:H7 from the less-toxic serotypes is the presence of bloody diarrhea, caused by the erosion of the lining of the large intestine by the bacteria s toxin. The result of this discovery is that meat processing plants have begun to use more comprehensive testing methods and sanitary measures in the handling and processing of the carcasses, and the food establishments are following the guidelines for minimum-temperature cooking and prevention of cross-contamination by proper food handling procedures.

There are probably other strains of E. coli that have not yet been discovered. Scientists are developing new testing techniques to differentiate between the strains, and between other closely related bacteria. The result of these discoveries is the increased safety of the American food and water supplies.

Although there are many ways of contracting coliform diseases, there are some simple measures to prevent infection:

1) Washing of hands with anti-bacterial soap and hot water before eating

2) Cooking meats to above 68o C. [155o F] or until pinkness is gone

3) Routine testing of water supplies

4) Immediate medical care in the event of accident or internal injury

5) Proper handling of raw foods to prevent cross-contamination

6) Proper storage of raw meats

By following these simple precautions, one can dramatically decrease the chance of coliform infection. The young, the elderly and the immuno-compromised must be extremely careful of contamination of food, water and milk with coliform bacteria.

BIBLIOGRAPHY

1. Brown, David. Tracing an Epidemic to a Mysterious Microbe, Washington Post National Weekly Edition. February 15-21, 1993. P. 38.

2. Libkin, L. DNA Repair Enzyme: A Structure Revealed, Science News. July 8, 1995. P. 36.

3. Meeker-Lowry, Susan. Challenging the Meat Monopoly, Z Magazine. March, 1995. P. 28-35.

4. Papinchak, Steve. Killer Bacteria E. coli O157:H7 is Old Villain, Las Vegas Review-Journal & Sun. January 31, 1993. P. 1A+.

5. Park, Hee-Won. Crystal Structure of DNA Photolyase From Escherichia coli, Science. June 30, 1995. P. 1866-1872.

6. Puzo, Daniel P. On the Hamburger Trail, Los Angeles Times. September 22, 1994. P. H1+.

7. Tomlinson, Stewart. Families in Fear, Oregonian. January 31, 1993. P. A1+.

Grade Received: A- High School: Honors Biology