BACKGROUND
Bacteriological analysis of water is performed to check the number of bacteria the water is contaminated with or simply it is a basic test for knowing about the water quality. The complete analysis consists of series of test to identify the bacteria. It mainly consists of three test presumptive test, confirmed test and completed test. So, the basic objective of this test is identification of various bacteria present in a water sample.
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REQUIREMENTS
Apparatus: Durham tubes containing lactose broth triple strength with Bromo thymol blue-3 no’s
Durham tubes containing lactose broth regular strength with Bromo thymol blue-6 no’s
Collection bottles with sterile water
Sterile pipette – 10 ml and 1 ml
PROCEDURE
Presumptive test
Take 50 ml of the water sample and shake it well. Then transfer 10 ml of this sample to each of the triple strength lactose tubes. After mixing well, transfer 1 ml of this sample to regular strength lactose tube. Then place it in incubator at 370C for 24 hours.
Confirmed test
Examine the tubes from presumptive test for acid/gas production. If no gas is produced then it is negative presumptive test.1 If any gas/acid is produced compare it with MPN (most probable number).Tubes showing more than 10% gas is taken for completed test.
Take one loopful of this positive presumptive test sample and streak it on EMB plate. Then incubate this at 37°C for 24 hrs. For better result, the positive presumptive ones can be collected and one ml of each can be inoculated to Brilliant Green lactose bile Broth (BGLB) tube, after incubating at 45°C for 24 hrs; then the tubes containing both gas and turbidity were to be considered positive for faecal coilforms.
Completed test
This test is for confirmation of coliform bacteria.The plates are observed for well formed coliform colonies, by seeing any colonies of blue black with metallic green sheen on the plates. Then these colonies are inoculated in NA slant and lactose fermentation tube and incubated at 37°C. Then the colonies from lactose broth are checked for gas production and colonies from NA slant is taken for gram staining.1
CONCLUSION
These three steps give a complete detail about the number of different bacteria present in water sample.
REFERENCES
- Baker FJ, Breach MR. Medical microbiological Techniques, xii. 1980: 547.
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