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Microorganisms That May Be Found In Drinking Water

A Colilert test is the routine test to determine if coliforms are absent or present in drinking water. Coliforms are a group of bacteria that are normal inhabitants of the intestinal tract which include Escherichia (or E. coli.), Klebsiella, Enterobacter, and Citrobacter. All but E. Coli. may also be found in the soil 1. Coliform bacteria may be accompanied by pathogens (i.e., pathogenic bacteria, viruses, protozoa, and helminths) in sewage and in wastewater. Sewage and wastewater could potentially contaminate a private well and thus contaminate the drinking water 2. The colilert test allows the use of coliforms as an indicator for routinely evaluating drinking water for the presence of pathogens. Testing for coliforms as opposed to pathogens is more reliable and less time consuming 1.

The colilert test first indicates either the presence or absence of total coliforms. Of these four bacteria, only E. coli. can be specified. The presence of coliforms in the absence of E. coli. suggests that the naturally occurring bacteria from the soil possibly entered the well through runoff or some other means. The presence of coliforms and E. coli indicates that fecal contamination has occurred and pathogens may be present. 

Coliform bacteria are rarely pathogenic, but there are a few exceptions. Certain strains of E. coli have been associated with gastrointestinal infections in adults, known as traveler's diarrhea or Montezuma's revenge, urinary tract infections, and newborn meningitis. Certain strains of Klebsiella pneumoniae have been associated with gastrointestinal infections, pneumonia, hospital-acquired urinary tract infections, burn wound infections, or as secondary invaders in other respiratory infections. Enterobacter has been associated with hospital acquired urinary tract infections. Citrobacter has been associated with hospital-acquired urinary tract infections, superficial wound infections, osteomyelitis, neonatal meningitis, and gastroenteritis 3. For more information on E. coli look up the EPA fact sheet on the EPA website located in the sidebar.

The principle bacteria pathogens that have been shown to cause human intestinal disease associated with drinking water are: Salmonella typhi, Typhoid fever; Salmonella paratyphi-A, paratyphoid fever; other Salmonella species, salmonellosis, enteric fever; Shigella dysenteriae, S. Flexneri, and S. sonnei, bacillary dysentery; Vibrio cholerae, cholera; Leptospira sp., leptospirosis; Yersinia enterocolitica, gastroenteritis; Francisella tularensis, tularemia; Escherichia coli. (specific strains), gastroenteritis; and Pseudomonas aeruginosa, various infections. The infecting dose varies with the strain as well as the age and general health of the host. Infants, the aged and the immunocompromised may be particularly susceptible 2

The principal viral pathogens that may be transmitted by drinking water from sewage or wastewater are the enteric viruses (i.e., acid stable picornaviruses), reoviruses, adenoviruses, and hepatitis A. People infected by these ingested viruses do not always become ill, but a disease involving the gastrointestinal system, central nervous system, skin, and heart is possible 2.

The principle protozoa pathogens that may be transmitted by drinking water from sewage or wastewater are Entamoeba histolytica, Giardia lamblia, and Cryptosporidium 2,3. Entamoeba histolytica is considerably more prevalent in tropical and subtropical areas. Cryptosporidium and G. lamblia are most frequently seen in rural and lower socioeconomic areas, but these protozoa may be found in drinking water that has been contaminated by sewage. People infected by these protozoa may not have any symptoms. Symptomatic victims may complain of abdominal cramps and diarrhea 3

The principle intestinal worms that are transmitted in drinking water include Ascaris lumbricoides, the round worm; Trichuris trichiura, the whipworm; Ancylostoma duodenale and Necator americanus, the hookworms; and Strongyloides stercoralis, the threadworm. It is unlikely that the transmission of helminthic infections into drinking water is significant 2

Chemical disinfection utilizing some form of chlorine remains the choice for disinfecting private wells. Chlorine has been shown to be an effective disinfectant for bacteria and viruses, but standard knowledge of the vulnerability of protozoa and helminths to chlorine is incomplete. It is known that protozoa and helminths are more resistant to chlorine than bacteria. The presence of coliforms or E. coli would warrant chlorination because of the potential risk for infection 2,3. The current NC groundwater quality standard for the coliform organisms is 1 per 100 milliliters (15NCAC 2L.0202), and a new standard is proposed at zero. The EPA maximum contaminant goal (MCGL) for Cryptosporidium, Giardia lamblia, viruses, and total coliforms is 0 mg/L 4 

There is a group of nuisance organisms collectively designated as iron, sulfur bacteria, and sulfate-reducing bacteria that may be found in drinking water. These bacteria are not pathogenic and are naturally found in the soil. These nuisance bacteria are responsible for various transformations of iron usually in the form of slime and often cause a bad odor and/or taste in the water. In addition, iron bacteria may cause plugging of well AND A REDDISH TINGE TO THE WATER. Sulfur and sulfate reducing bacteria may cause rusty water and corrosion of pipes 5

Iron bacteria are most likely to appear in water with relatively high iron concentrations (i.e., 10 to 30 mg/L), but may develop in water with low iron concentrations (0.1 to 0.3 mg/L) if the supply of iron is continuously renewed. Iron bacteria oxidize ferrous iron to ferric iron and cause the precipitation of ferric hydrate. The precipitation of ferric hydrate causes a foul odor and taste and reddish tinge to the water 5

Sulfur bacteria oxidize sulfur to sulfate while sulfate-reducing bacteria reduce sulfate to hydrogen sulfide. These products cause a foul odor and taste to the water. Sulfur bacteria may bring large amounts of iron into solution under conditions favorable for its development. The hydrogen sulfide produced from the sulfate-reducing bacteria reacts with dissolved iron to form black insoluble iron sulfide. Chlorination is used to control these nuisance organisms as well as decreasing the iron, sulfide, and/or sulfur content for the water 5

Luanne K. Williams, Pharm.D., Toxicologist, 
Medical Evaluation and Risk Assessment Unit, 
North Carolina Department of Health and Human Services

Daves L, 1995. Laboratory Supervisor, Environmental Microbiology Branch of the State Laboratory of Public Health. Personal Communication.

2 National Research Council: Drinking Water and Health Disinfectants and Disinfectant By-Products. National Academy of Sciences, Volume 7, National Academy Press, 1987. 

3 Volk WA et al, 1986. Essentials of Medical Microbiology. 3rd ed. Philadelphia: J.B. Lippincott Co. 

4 USEPA 1996. U.S. Environmental Protection Agency. Drinking Water Regulations and Health Advisories.

5 Starkey RL, 1945. Transformations of Iron by Bacteria in Water. Journal of the American Water Works Association, Vol. 37, No.10. pp. 963-983.


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