bacteriological techniques. Therefore, rather than look for specific' pathogens, the
sanitary microbiologist looks for indicator organisms which will indicate the probability
that pathogens exist in water. Bacteria of the genera Escherichia and Enterobacter,
known as coliform bacteria, are readily identified by their ability to ferment lactose, with
the production of gas (subsequently confirmed by other tests). Since Escherichia and
Enterobacter are normal inhabitants of the human intestinal tract, their presence in
water is considered prima facie evidence of fecal contamination. Diseases such as
cholera, typhoid fever, shigellosis, amebic dysentery, and various helminthic infestations
are known to be transmitted through water contaminated with infected human feces.
Therefore, the presence of coliform bacteria in water is considered a strong possibility
that pathogenic organisms are also present. Accordingly, water that shows the
presence of coliforms is not considered potable until it has been treated by disinfection
(chlorination).
e. Sampling. Bacteriological tests should be made whenever a new source of
water is proposed and should be conducted periodically on all existing sources.
(1) Frequency and distribution of samples. TB MED 576, Sanitary Control
and Surveillance of Water Supplies at Fixed Installations, prescribes that a minimum of
eight monthly samples for coliform determination will be collected at each fixed
installation. If the population served is greater than 1,000, an additional sample for
1,000 people will be collected. Sampling points must be representative of the entire
installation, and one-fourth of the samples are to be collected each week, so that during
the month all points will be progressively covered. Sampling points must be of water
distributed for drinking and culinary purposes (that is, dining facilities, hospitals,
barracks, and so forth.)
(2) Sample bottles. Bottles used for bacteriological samples may be of any
suitable size and shape, but wide-mouthed, ground glass stoppered bottles, of
borosylicate glass or polypropylene, are preferred. Metal or plastic screw cap closures
may be used provided they are capable of withstanding sterilization without producing
toxic or bacteriostatic compounds, or without losing their original configuration and
watertight seal. Sample bottles must be thoroughly washed, rinsed in clean (preferably
distilled) water enough times to insure the removal of any residual washing compound
or detergent, and sterilized by one of the methods described in paragraphs 3-4 and 3-5.
The stopper and neck of the bottle are covered with a hood prior to sterilization. Each
sample bottle is submitted to the laboratory accompanied by DD Form 686
(Bacteriological Examination of Water) (figure 3-3).
MD0151
3-4