Indicators Of Fecal Contamination Coliform And Streptococci Bacteria

Background

Detecting and preventing fecal contamination is of prime importance for all drinking water systems and recreation water managers. Fecal wastes may contain enteric pathogens (disease-causing organisms from the intestines of warm-blooded animals) such as viruses, bacteria, and protozoans (which include Cryptosporidium and Giardia). Fecal contaminated water is a common cause of gastrointestinal illness, including diarrhea, dysentery, ulcers, fatigue, and cramps. It also may carry pathogens that cause a host of other serious diseases, such as cholera, typhoid fever, hepatitis A, meningitis, and myocarditis.

So far, testing water directly for individual pathogenic organisms is impractical for several reasons, including

• There are so many different kinds of pathogens that a comprehensive analysis would be very expensive and time consuming. Time is of the essence for pathogen detection.

• Pathogens can be dangerous at small concentrations. They require large sample volumes for analysis which add to the time and cost of analysis.

• Reliable analytical methods for several important pathogens are difficult or not even available. Also, not all water-borne pathogenic microorganisms are known.

• A satisfactory alternative is available, namely the identification of "indicator" species that are easy to measure and are always present with enteric pathogens.

Hence, awareness of possible contamination by enteric pathogens is based on detecting the more easily identified "indicator" species whose presence indicates that fecal contamination may have occurred.

The five indicator species most commonly used today are total coliforms, fecal coliforms, Escherichia coli (E. coli), fecal streptococci, and enterococci. All are bacteria normally present in the intestines and feces of warm-blooded animals, including humans. All but E. coli consist of groups of bacterial species that are similar in shape, habitat, and behavior. E. coli is a single species within the fecal coliform group. These indicators themselves are usually not pathogens and do not pose a danger to humans or animals. However, if the indicators are present in water, the accompanying presence of enteric pathogens is a possibility.

All the indicator species are easier to measure than most pathogens but are harder to kill. Therefore, treatment that satisfactorily destroys the indicator species may be assumed to have also destroyed enteric pathogens that were present. For example, in waste water disinfection, it is assumed that a decrease in fecal coliforms to <200 fc/100 mL will have eliminated the great majority of pathogens.

Total coliforms and fecal coliforms are the "old reliable" indicators of fecal contamination, used since the 1920s to protect public health. However, both have limitations that stimulate regulators to continue seeking improved methods.

Total Coliforms

Total coliform bacteria are widespread in nature. In addition to their animal intestine habitat, they occur naturally in plant material and soil. Therefore, their presence does not necessarily indicate fecal contamination. Total coliforms are not recommended as indicators of recreational water contamination, where they are usually present from soil and plant contact. Total coliforms are the standard test for contamination of finished drinking water, where contamination of a water supply or distribution system by fecal, plant, or soil sources is not acceptable. Federal drinking water standards are based on total coliform bacteria. The EPA maximum contaminant level (MCL) for drinking water is zero total coliforms per 100 mL of water for 95% of samples after treatment (chlorination, ozonation, UV). See Appendix A.

Fecal Coliforms

Fecal coliforms are a more fecal-specific subset of total coliform bacteria. However, even the fecal coliform group contains a genus, Klebsiella, with member species not necessarily fecal in origin. Klebsiella coliforms are found in large numbers in textile, pulp, and paper mill wastes. Fecal coliforms are widely used to monitor recreational waters and are the only indicator approved for classifying shellfish waters by the U.S. Food and Drug Administration's National Shellfish Sanitation Program. On the basis of statistical data, the EPA has recently begun recommending E. coli and enterococci as better indicators of health risk from water contact. However, many states still use fecal coliforms for this purpose, in part so that new data can be directly compared with historical data.

Natural surface waters almost always contain some background level of fecal coliforms, usually less than 15-20 fc/100 mL MPN (most probable number). In sewage entering a waste treatment plant, the fecal coliform count may be over 10 million fc/100 mL (fecal coliforms per 100 mL of sample). Satisfactory disinfection of secondary effluent from a waste treatment plant is defined by an average fecal coliform count of <200 fc/100 mL. Fecal coliforms are normally absent after wastewater percolates through 5 ft of soil.

State water standards for fecal coliform levels vary, but typical state standards are (geometric mean values)

• Class 1 primary contact recreational 200 fc/100 mL

• Class 1 secondary contact recreational 2000 fc/100 mL

• Domestic water supply (before treatment) 2000 fc/100 mL

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Responses

  • Layton
    Which microbe is a true indicator of fecal contamination?
    20 days ago

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