Microbiology Analysis of Drinking Water
INTRODUCTION
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.
6. 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.[Copyright note: http://www.labreports.info]
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.
Unfortunately the coliforms include a wide range of bacteria whose primary source may not be the intestinal tract.
To deal with this difficulty, tests have been developed that allow water to be tested for the presence of faecal coliforms (i.e. E.coli). These are coli-forms derived from the intestine of warm-blooded animals, which can grow at the more restrictive temperature of 44.5°C.
The method offers a safety condition against most bacterial pathogens, but is not effective against some other bacteria, viruses and protozoan parasites. For example, the deadly E. coli O157 may be present even when faecal coliform measurements show negative.
Furthermore, viruses and most protozoan parasites, such as Giardia and Cryptosporidium, are resistant to chlorination and filtration, which usually kill coliform bacteria.
As a result, coliform bacteria cannot be accurate indicators in such cases, particularly in chlorinated waters.
(Like bacteria, protozoans and viruses are also passed via animal faeces).
Discussion and Conclusion
One of the main requirements for drinking water is that it must be free of coliforms.
The presence of coliforms (including E.coli Enterobacter aerogenes, and klebsiella pneumoniae) may be identified by presumptive coliform test, because of the gas and acid production.
This is due to the fact that coliforms can produce gas (following the lactose fermentation) and acid at 37°C.
Generally the presence of coliforms including E.coli, Enterobacter aerogenes, and klebsiella pneumoniae are usually determined by presumptive coliform test; when turbidity and gas are produced.
Turbidity and gas production at 44°C imply the presence of faecal conliforms i.e. E.coli.
E.coli is considered as foreign enteric indicator bacteria when they are present in water, then the water can’t be appropriate for human consumption.
Presence/absence of faecal conliforms can also be observed microscopically (using a gram stained smear of selected colonies); gram negative, rod shaped cells would be searched as characteristics of faecal coliform.
Faecal streptococcus can also be identified by microscope; gram-positive, catalase-negative cocci from the stained smear of suspected colonies produced on incubated media.
Due to the fact that faecal coliforms and faecal streptococci and Clostridium perfringens are highly likely to exist in the gut of all warm-blooded animals, their presence in water supplies will necessitate immediate action to remove the source of faecal pollution.
(These organisms are normally controlled through the disinfection of water).
In conclusion, the presence of coliform group, streptococcus faecalis, clostridium perfringens are not themselves considered as hazard but they implicate that faecal matter has entered the supply and therefore the contamination with more dangerous organisms. [1025]
