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Bacteriological Analysis of Water

According to the World Health Organization, the bacterial analysis of water provides the most responsive test for hazardous fecal contamination. A source for drinking water should be tested frequently; however, complex tests for specific pathogens can be time-consuming and costly. Thus simple tests for intestinal pathogens that cause typhoid fever and dysentery can indicate the type of pollution as well as corresponding treatment.

  1. Test Limits

    • Due to the diversity of human fecal pathogens--protozoa, viruses, bacteria—the task of detecting individual pathogens in water is untenable. However, an organism that normally inhabits the intestinal tract of warm-blooded animals, E. Coli, does not exist in fresh water. If it’s discovered in water, then fecal contamination can be assumed, according to Western Washington University. Different tests are available to determine whether the water supply contains coliforms, a group that contains E. Coli.

    Total Count

    • The total count test (also standard plate count and colony count) yields the aggregate number of microorganisms in a water sample. The water to be tested is first mixed with liquefied Yeast-Extract Agar, and then poured into petri dishes to solidify. While one set of plates are incubated for three days at 20 to 22°C, another set is incubated at 37°C for a full day. The bacteria that thrive in water will do so more readily at the lower temperature. Both sets are then counted separately. The total count test is most often used to assess the sanitation of a water distribution system or the fitness of a large water supply for food and beverage preparation, reports Microbiologyprocedure.com.

    Multiple Tube Test

    • Varying amounts of the water sample are poured into tubes filled with a culture medium. If the water is contaminated, the bacteria will reproduce and generate acid with gas or without. According to the World Health Organization, the most probable number (MPN) of bacteria in the initial water sample can be statistically deduced from the number of tubes inoculated and the number with a positive response. The multiple-tube method can be employed to gauge many kinds of water, ranging from sewage to soil specks.

    Membrane Filter Method

    • When the number of contaminant bacteria in the water sample is low, membrane filter (MF) techniques offer an effective route to isolate particular colonies of bacteria. In this method, a 100 mL water sample passes through a 47 mm membrane with not only a filter funnel but also a vacuum system. Bacteria caught on the membrane surface are then placed in a petri dish with a suitable medium. After incubation, the bacteria produce colonies which can then be measured, reports the Pall Corporation.

    Disease Transmission

    • Several kinds of disease outbreaks can result from water containing fecal bacteria. In recent history, the most frequently occurring outbreaks have been typhoid fever (Salmonella typhi) and bacillary dysentery (Shigella). In addition, cholera and other types of dysentery (Camphylobacter and Escherichia coli), and also viruses such as hepatitis and polio, have been discovered in contaminated water, reports the Public Health Museum in Massachusetts.

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