Screening of Coliform group of bacteria and waterborne pathogenic bacteria from ground- water samples from Vasai, Thane district

The present study was carried out to study the microbiological characteristics of ground water samples collected from wells and bore wells near Mumbai. Samples were screened for coliform bacteria and waterborne pathogenic bacteria. The results indicated that all the water samples are highly polluted and not potable.


Enrichment of coliform group of bacteria (E. coli ) Presumptive test
Enrichment cultures were prepared in lauryl tryptose broth of single strength (6 tubes) and double strength (3 tubes) according to the size of water sample i.e. 0.1 ml & 1ml of sample in 5 ml single strength broth and 10ml of sample in 10 ml double strength broth.0.1 ml water sample was dispensed in each tube 1, 2, 3 and 1 ml in each tube 4, 5, 6 and 10 ml in 7, 8, 9.All the tubes were incubated at 35°C for 24-48 hours for the gas production.After incubation, the most probable number (MPN) of coliforms i.e MPN index per 100 ml was found out (Dubey and Maheshwari, 2002).

Confirmed test
For confirmation of a positive result in the presumptive test 0.2 ml of broth is inoculated into Brilliant green lactose bile broth (BGLB) tube.If gas is seen in the BGLB tube it indicates that the gas in the presumptive test tubes was indeed produced by the coliforms.

Salmonellae and Shigellae
Enrichment cultures were prepared by adding 5 ml of water sample to 100 ml of flask containing 50 ml of Selentine broth.Incubation was at room temperature under static condition.Bacterial growth was monitored every 2 days.

Vibrio
Enrichment cultures were prepared by adding 5 ml of water sample to 100 ml of flask containing 50 ml of Alkaline peptone water.Incubation was at room temperature under static condition.Bacterial growth was monitored every 2 days.

Streptococcus faecalis
Enrichment cultures were prepared by adding 5 ml of water sample to 100 ml of flask containing 50 ml of Azide dextrose broth with BCP.Incubation was at room temperature under static condition.Bacterial growth was monitored every 2 days.

Isolation and characterization of coliform & pathogenic bacteria isolation
Bacteria from each enriched broth were isolated on selective plates according to the type of bacteria under study.Isolation was carried out in duplicates.EMB agar was used for E. coli, SS agar for Salmonella and Shigella spp., TCBS agar was used for Vibrio spp.Whereas Bile Esculin Azide agar was employed for isolating Streptococcus faecalis.The plates were incubated at 37°C for 24 to 48 hours and the number of colonies on each plate was noted (Hi Media, 1998).

Characterization and identification of the bacteria
The morphological features such as colour, size, margin, elevation and gram's nature of each colony were noted.The isolated organisms were then maintained on nutrient agar slant overlayed with paraffin oil.The bacterial isolates were identified on the basis of Bergey's Manual of Systematic Bacteriology (Brenner et. al., 2005).

RESULTS AND DISCUSSION
It is not practical to test water directly for every possible disease-causing bacterium, virus, and protozoan, so the water is tested instead for a group of indicator bacteria, which measure the sanitary protection of the well and water system.This group of common bacteria, called the "total coliform group," is a good indicator of sanitary protection.Most coliform bacteria do not themselves usually cause disease, but they can indicate that surface contamination has somehow gotten into the water, and disease organisms may also be present.Pathogenic organisms found in water may be discharged by human beings who are carriers of a particular disease.These organisms are highly infectious and are responsible for many thousands of deaths each year.Hence screening of coliform bacteria and pathogens was carried out to analyse the potability of the water samples.
As seen in table 1, all the water samples were found to contain coliform bacteria E. coli which were selectively isolated on EMB agar.
Isolation of coliform and pathogenic bacteria on SS agar indicated that all the six water samples contained Salmonella and Shigella spp.(Table 2).TCBS agar was employed for isolation of Vibrio cholerae and agar plates after incubation showed presence of Vibrio cholerae in all the water samples under study (Table 3).
Table 4 shows that isolation on Bile Esculin azide agar suggests that sample 4 and sample 6 contained Streptococcus faecalis.
The results of the present study indicate that water samples under study contained pathogenic bacteria such as Vibrio cholerae , Streptococcus faecalis and coliform group of bacteria such as E. coli indicating that all the water samples are highly contaminated and not potable which was confirmed by Most Probable Number and isolation, enrichment and characterisation of coliform and pathogenic bacteria on selective media (Table 5).If such water samples are consumed for industrial and house hold work, then they can be quite harmful to human health.Thus, it is advocated that prior to their use for human consumption, such ground water samples from wells and bore wells must be microbiologically anlysed to prevent various infectious diseases.