Bacteria are common single-celled organisms and are a natural component of lakes, rivers, and streams. Most of these bacteria are harmless to humans; however, certain bacteria, some of which normally inhabit the intestinal tract of warm-blooded animals, have the potential to cause sickness and disease in humans. High numbers of these harmless bacteria often indicate high numbers of harmful bacteria as well as other disease-causing organisms such as viruses and protozoans.
Total coliforms are gram-negative, aerobic or faculative anaerobic, nonspore forming rods. These bacteria were originally believed to indicate the presence of fecal contamination, however total coliforms have been found to be widely distributed in nature and not always associated with the gastrointestinal tract of warm blooded animals. The number of total coliform bacteria in the environment is still widely used as an indicator for potable water in the U.S.
Fecal coliform bacteria are a subgroup of coliform bacteria that were used to establish the first microbial water quality criteria. The ability to grow at an elevated temperature (44.5 C) separate this bacteria from the total coliforms and make it a more accurate indicator of fecal contamination by warm-blooded animals. Fecal- coliform bacteria are detected by counting the pink-red colonies that grow on 0.65 micron filters placed on mFC agar incubated in a 44.5 C oven for 22-24 hours. The presence of fecal coliforms in water indicates that fecal contamination of the water by a warm-blooded animal has occurred, however, recent studies have found no statistical relationship between fecal coliform concentrations and swimmer-associated sickness.
Escherichia coli (E. coli) is a rod-shaped bacteria commonly found in the gastrointestinal tract and feces of warm-blooded animals. It is a member of the fecal coliform group of bacteria and is distinguished by its inability to break down urease. E. coli numbers in freshwater are determined by counting the number of yellow and yellow brown colonies growing on a 0.45 micron filter placed on m-TEC media and incubated at 35.0 C for 22-24 hours. The addition of urea substrate confirms that colonies are E. coli. This bacteria is a preferred indicator for freshwater recreation and its presence provides direct evidence of fecal contamination from warm-blooded animals. Although usually harmless, E. coli can cause illnesses such as meningitis, septicemia, urinary tract, and intestinal infections. A recently discovered strain of E. coli (E. coli 0157:H7) can cause severe disease and may be fatal in small children and the elderly.
|The relation between bacteria counts and sickness
Consumption of or contact with water contaminated with feces of warm-blooded animals can cause a variety of illnesses. Minor gastrointestinal discomfort is probably the most common symptom; however, pathogens that may cause only minor sickness in some people may cause serious conditions or death in others, especially in the very young, old, or those with weakened immunological systems.
As these charts show, studies have shown that there is not a positive relation between either total coliform or fecal coliform counts and sickness. But, studies have shown a positive relation between E. coli and sickness -- as E. coli counts go up, the occurrences of sicknesses go up. That is why this project is focusing on E. coli as the main indicator of potential risk.
USEPA criteria for E.coli bacteria
|Human health water-quality criteria are numeric values that are intended to limit chemical or microbiological pollutants in ambient water. Each state develops water-quality criteria based upon criteria determined under Section 304(a) of the Clean Water Act of 1972. These criteria are based solely on data and scientific judgment relative to pollutant concentrations and environmental and human health effects. The values of the standards must be established to support the predominant use of the water body. Such uses include drinking water, body contact recreation, fishing, and aquatic life maintenance. The standards developed by a state can be more stringent than the criteria but not more lenient.
The water-quality standard for the Escherichia coli indicator bacteria (E. coli) is 235 cells or colony forming units (CFU) per 100 mL of a single water sample, or 126 cells or CFU per 100 mL as a geometric mean from at least four water samples.
The USEPA has determined that higher E.coli bacteria counts indicate that people who come into contact with the water may have a greater probability of illness. But it is important to remember that as E.coli counts go up, it is the chance that someone will get sick that goes up - there are many other things that determine if a person will become sick:
- how long someone is in contact with the water
- if water come into contact with a person's mouth or eyes
- if the person has any skin abrasions that will allow water to enter the body
- the age and health of the person
- a compromised immune system (HIV infected, transplant patients)
When E. Coli counts exceed 235, there is a statistically greater risk that more than 8 people out of 1,000 people using the river will experience stomach illness.
National Park Service health-risk determinations
Low risk: E. coli counts of less than 177 colonies per 100 mL of water
As determined by the U.S. Forest Service, a person in direct contact with the river water (i.e. swimming, diving, wading) has a LOW chance of getting sick. The water is in full compliance with recreation water-quality criteria.
High risk: E. coli counts above 235 colonies per 100 mL of water
Contact with the river is NOT recommended. A person in direct contact with river water has an increased risk of getting sick. The water quality does NOT meet federal recreation water-quality criteria.