Microbiological Parameters of Water Quality

Microbiological Indicators of Water Quality

The drinking water should be free from pathogenic microorganisms. The biological/ microbiological quality of water is assessed by examining the water sample for indicator organisms.

Indicators Organisms

The indicator organisms are those microorganisms, whose presence in water indicates the presence of potential pathogenic microorganisms. The indicator organisms are used in water safety and quality control procedureswhen thepotential pathogenic microorganisms cannot be detected with ease and reliability.

Properties of Indicators Organisms

1. Indicator organisms should be useful for all types of water.
2. Indicator organisms should be present whenever a pathogen is present.
3. Indicator organisms should have long survival time (more than pathogen).
4. The organisms should not grow on water.
5. Indicatororganisms should be detected by an easy procedure.
6. Their number should have adirect relation to the degree of pollution.
7. Indicator organisms should be a member of intestinal microflora.

The different types of indicator organisms are:

Total Coliform

This group includes facultatively anaerobe, gram-negative, non-sporulation, catalase positive, oxidase negative, rods that ferments lactose and produce gas during incubation in a prescribed culture medium within 48 hours at 35°C-37°C. This group includes the genusEscherichia, Citrobacter, Klebsiella, and Enterobacter.The number of coliform bacteria depends on the types and amount of organic matter present in water and temperature of water. Their number is increased when the temperature of thewater is elevated and if the concentration of organic matter is increased. They are used as indicator organisms because:

• They can grow in an aquatic environment.
• Thier presence is interrelatedwith bacterial, protozoan and other pathogens (usually enteric).
• Long survival.
• Easy detection.
• Constant presence on GI tract of humans (their presence indicates fecal contamination).

Fecal Coliforms/ Thermotolerant Coliform

Many coliforms are not limited to fecal sources and their presence in the water may be misinterpreted as fecal contamination/pollution. To overcome this problem, the methods have been developed to restrict the detection of coliforms that are more clearly of fecal origin only. The coliforms that are exclusively present in the fecal matter are called fecal coliforms. The fecal coliforms include Escherichia and Klebsiella. These fecal coliforms can be differentiated from other coliforms by their ability to ferment lactose with the production of acid and gas at 44.5°C (44±0.5°C).

Fecal coliforms are less resistant to the water treatments and regrow in the water.

Fecal Streptococci

Of the faecal streptococci, the preferred indicators of faecal pollution are the enterococci. The predominant intestinal enterococci being E. faecalis, E. faecium, E. durans and E. hirae. In addition, other Enterococcus species and some species of Streptococcus (namely S. bovis and S. equinus) may occasionally be detected. These streptococci however, do not survive for long in water and are probably not enumerated quantitatively. Thus, for water examination purposes enterococci can be regarded as indicators of faecal pollution, although some could occasionally originate from other habitats.

The fecal coliform and fecal streptococci in the ratio of 4 or more indicatecontamination of humanorigin whereas the ratio below 0.7 indicates the pollution of animal origin. The Enterococci are useful indicators of the presence of enteric viruses as well. There are certain advantages of using fecal Streptococci as indicators:

• They rarely multiply in water.
• They are more resistant to chlorination and environmental stress than coliforms.
• They generally persist for alonger duration.

Clostridium perfringens

It is a Gram-positive rod-shaped, anaerobic,sulfide reducing, spore former bacteria exclusive to afecal origin. The spores are usually heat resistant (75°C for 15 mins). C. perfringens is the species of clostridia most often associated with the faeces of warm-blooded animals , but is only present in 13–35% of human faeces. The anaerobic sulphite-reducing clostridia are much less prevalent than bifidobacteria in human faeces, but their spore-forming habit gives them high environmental resistanceIt could be an indicator of past pollution (spores) or a recent pollution (vegetative cells). However, the spores are of limited use as an indicator. Along withClostridium perfringens,other anaerobic bcteria of fecal origin such asBifidobacterium andBacteroides.

Virus/ Coliphage

The bacterial viruses are considered as appropriate indicators of fecal pollution because of their constant presence in the sewage and pollute water. It is assumed that their presence in the water sample indicates the presence of bacteria capable of supporting the replication of phage. These are bacterial viruses and are ubiquitous in the environment. For water quality testing and to model human enteric viruses, most interest in somatic coliphages, male-specific RNA coliphages (F-RNA coliphages) and phages infecting Bacteroides fragilis.The most widely used bacteriophage include coliphage that infectsE. colistrains. Coliphage such as F2,Φ174, etc. are used as indicators. The DNA containing tailed coliphages (T type) and RNA-containing phages that infect via the F-pili (sex factor) (F-RNA coliphages) have been the most used.Plating as well as MPN can be used to detect the coliphage in the volumes of water ranging from 1 ml to 100 ml.

Faecal sterol biomarkers

The presence of faecal indicator bacteria gives no indication of the source, yet it is widely accepted that human faecal matter is more likely to contain human pathogens than animal faeces. The detection of human enteric viruses is specific, however; the methods are difficult and expensive, and not readily quantifiable. sing more than one method of determining the degree of sewage pollution would be prudent and advantageous. The use of alternative indicators, in this case faecal sterols as biomarkers, in conjunction with existing microbiological indicators, offers a new way to distinguish sources of faecal contamination and monitor river ‘health’.

References

Atlas, RM and R Bartha. Microbial Ecology:Fundamentals and Applications. The Benjamin Cummins Publication co. Inc., 1998.

Gordis, L. Epidemiology. third edition. 2004.

Maier, RM, IL Pepper and CP Gerba. Environmental Microbiology. Academic press Elsevier Publication, 2006.

Park, K. Park's Text Book of social and prevention Medicine. 18th edition. 2008.