Detection of Microorganisms in Environmental Freshwaters and Drinking Waters

The presence of some microorganisms in waters is used as an indication of possible contamination and as an index of quality deterioration. Gastroenteritis is the most common affliction associated with waterborne pathogens. The ideal manner to determine the microbiological safety of waters is to analyze the waters for the presence of specific enteric pathogens; however, hundreds of different microorganisms have been shown to be involved in waterborne disease outbreaks; thus, it would be impractical to look for every pathogen potentially present in water samples. Bacteroides fragilis is a strict anaerobe found in high concentrations in the human intestinal tract and dies rapidly when discharged into environmental waters. The ratio of fecal coliforms to fecal streptococci was proposed as an indicator of the origin of the contamination because of the different concentrations at which these microorganisms are present in different animals and humans. The detection of thermotolerant coliforms in treated drinking waters should be a cause for concern, since present drinking water treatment processes successfully eliminate indicator microorganisms. Most probable number (MPN) analysis is a statistical method based on the random dispersion of microorganisms in a given sample. Classically, this assay has been performed as a multiple-tube fermentation test. The practice of using groups of bacteria or specific organisms such as Escherichia coli as indicators of the possible presence of fecal contamination or as indicators of the possible presence of pathogenic microorganisms is and has been extremely useful to protect public health.