Drinking water supplies are prone to contamination with sewage or other excreted matter may cause outbreaks of intestinal infections such as typhoid fever.
Monitoring and detection of indicator and disease-causing micro-organisms are a major part of sanitary microbiology. By chlorinating drinking water supplies, control of most major disease-causing bacteria can be obtained.
The major concern is about the inability to consistently remove viruses and protozoa and to achieve quality standards for these micro-organisms.
Bacteriological tests must be performed constantly to ensure that drinking water supplies are safe for human consumption.
Primarily contamination of water with human faecal wastes would result in viral, bacterial, and protozoan diseases. Although many of these pathogens can be detected directly, environmental microbiologists have generally used indicator organisms as an index of possible water contamination by human pathogens.
Researchers are still trying to establish the ideal indicator organism to use in sanitary microbiology. The following are among the suggested criteria for such an indicator:
1. The indicator bacterium should be suitable for the analysis of all types of water: tap river, ground, impounded, recreational, estuary, sea, and waste.
2. The indicator bacterium should be present whenever enteric pathogens are present.
3. The indicator bacterium should survive longer than the hardiest enteric pathogen.
4. The indicator bacterium should not reproduce in the contaminated water and produce an inflated value.
5. The detailed procedure for the indicator should have great specificity; i.e. other bacteria should not give positive results.
In addition, the procedure should have considerable sensitivity and detection of the level of indicator.
. The testing method should be easy to perform.
7. The indicator should be harmless to humans.
8. The level of the indicator bacterium in contaminated water should have some direct relationship to the degree of faecal pollution.
Basically the following are analysed (to confirm the presence/absence of commensal bacteria of intestinal origin):
– The coliform group
– Streptococcus faecalis
– Clostridium perfringens
These do not themselves constitute a hazard but they imply that faecal matter has entered the supply and that the water is therefore liable to contamination with more dangerous organisms. The coliform bacilli are believed to be the most reliable indicators of faecal pollution.
Coliforms, including Escherichia coli, are members of the family Enterobacteriaceae. These bacteria make up approximately 10% of the intestinal micro-organisms of humans and other animals and have found widespread use as indicator organisms.
They lose viability in fresh water at slower rates than most of the major intestinal bacterial pathogens.
When such “foreign” enteric indicator bacteria are not detectable in a specific volume (100ml) of water, the water is considered potable or suitable for human consumption.
Coliform numbers are controlled through the disinfection of water.
Basically coliforms are defined as facultatively anaerobic, gram-negative, nonsporing, rod-shaped bacteria that ferment lactose with gas formation within 48 hours at 35°C.
The original test for coliforms corresponding this definition would involve the presumptive, confirmed, and completed tests.
The presumptive step is conducted by means of tubes inoculated with three different sample volumes to give an estimate of the most probable number (MPN) of coliforms in the water. The complete process, including the confirmed and completed tests, requires at least 4 days of incubations and transfers.
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