Are those organisms (specie) which are very sensitive to changes in the environment, and whose presence or absence may be indicative of environmental conditions in a particular area or habitat.
However, species composition and relative abundance of individual components of the population or community are usually considered to be a more reliable index of water quality.
Example: presence of E.coli in polluted water.
How indicators are used:
The variety and often low concentrations of pathogens in environmental waters makes them difficult to test for individually. Public agencies therefore use the presence of other more abundant and more easily detected fecal bacteria as indicators of the presence of fecal contamination.
What indicator can do?
Ø Indicator species are used to assess overall sanitation or environmental conditions.
Ø They signal or indicate the potential presence of pathogens of food safety concern.
Ø Used to act as an early-warning system.
Criteria in classification of Indicator organism:
Following factors are considered in classifying an organism as an indicator:
Ø Their strong association with fecal contamination.
Ø Their co-habitation with pathogens of concern.
Ø Simple and efficient testing procedure.
Ø Be easily detected using simple laboratory tests.
Ø Generally not be present in unpolluted waters.
Ø Appear in concentrations that can be correlated with the extent of contamination.
Ø Have a die-off rate that is not faster than the die-off rate of the pathogens of concern.
Ø The organism should not grow in water
Ø The organism should be found in warm-blooded animals’ intestines.
Types of organisms used as Indicator:
Bacteria and other organism which can be used as indicator of fiscal pollution in water and environment are as follow:
1. Coliform bacteria
2. E.coli
3. Enterococci
4. Clostridia
5. Streptococcus bovis
6. Molds etc
E. coli: is a species of fecal coliform bacteria that is specific to fecal material from humans and other warm-blooded animals. EPA recommends E. coli as the best indicator of health risk from water contact in recreational waters; some states have changed their water quality standards and are monitoring accordingly.
Fecal streptococci generally occur in the digestive systems of humans and other warm-blooded animals. In the past, fecal streptococci were monitored together with fecal coliforms and a ratio of fecal coliforms to streptococci was calculated. This ratio was used to determine whether the contamination was of human or nonhuman origin. However, this is no longer recommended as a reliable test.
Enterococci: are distinguished by their ability to survive in salt water, and in this respect they more closely mimic many pathogens than do the other indicators. Enterococci are typically more human-specific than the larger fecal streptococcus group. EPA recommends enterococci as the best indicator of health risk in salt water used for recreation and as a useful indicator in fresh water as well.
Total coliforms:
Total coliforms are a group of bacteria that are widespread in nature. All members of the total coliform group can occur in human feces, but some can also be present in animal manure, soil, and submerged wood and in other places outside the human body. Thus, the usefulness of total coliforms as an indicator of fecal contamination depends on the extent to which the bacteria species found are fecal and human in origin. For recreational waters, total coliforms are no longer recommended as an indicator. For drinking water, total coliforms are still the standard test because their presence indicates contamination of a water supply by an outside source.
DISEASES: Some waterborne pathogenic diseases include ear infections, dysentery, typhoid fever, viral and bacterial gastroenteritis, and hepatitis A.
Fecal Coliform Testing:
Fecal coliform bacteria are non disease causing organisms which are found in the intestinal tract of all warm blooded animals. Each discharge of body wastes contains large amounts of these organisms. The presence of fecal coliform bacteria in a stream or lake indicates the presence of human or animal wastes. The number of fecal coliform bacteria present is a good indicator of the amount of pollution present in the water.
Most waterborne disease-causing organisms originate in human or animal bodies and are discharged as part of body wastes. Due to the relatively small numbers of disease causing organisms, it is very difficult to isolate and identify specific disease causing bacteria. Since fecal coliform bacteria originate in the same location, they are used as an indicator of possible disease hazards in a body of water. The presence of very few fecal coliform bacteria would indicate that a water source probably contains no disease producing organisms, while the presence of large numbers of fecal coliform bacteria would indicate a very high chance that the water source could contain disease producing organisms.
Most Probable Number test:
The most probable number (MPN) of coliform or fecal coliform bacteria per unit volume of a sample. It is expressed as the number of organisms which are most likely to have produced the laboratory results noted in a particular test.The MPN method attempt, by serial dilution, to introduce one, and only one, bacteria into a fermentation tube containing media for the bacteria to thrive on.
By examining different volumes of sample, one-tenth multiples of 1 mL, it is possible to make an approximate estimate of the number of coliform bacteria present in the sample through consideration of the relative numbers of tubes in the various dilutions which yield positive and negative results. The estimation is in the form of a "most probable number index" which essentially is a concentration of coliform bacteria in the sample (expressed as the number of bacteria per 100 mL of sample) which would most probably yield the same combination of positive and negative tubes as obtained in the examination of the sample. The highest dilution giving positive results in all 5 portions tested and the next 2 succeeding higher dilutions are selected. The results of these 3 dilutions are then used in computing the MPN index. The calculated index will equal the tabular index multiplied by a factor equal to the denominator of the highest dilution giving positive results in all 5 tubes. For example, if all tubes in all dilutions are positive until the 1/1000 dilution is reached, we consider only the 1/1000 and 1/10,000 dilutions as significant. Suppose the results of analysis indicate that the positive tubes for these 3 dilutions are as follows:
1/100 5+ 0-
1/1000 4+ 1-
1/10,000 3+ 2-
The MPN index then equals 280 x 1000 = 280,000 coliform bacteria in 100 mL of the original sample.
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