AIM : To determine the potability of water by MPN Test
Water which receives animally & human which form a primary source of water borne disease. Direct testing procedures capable of detecting & quantifying the full spectrum of pathogens & identifying their source is time consuming process because of their variable occurrence, survival rate & origin; hence an indicator system has been identified as a best method for evaluating the microbiological quality of water.
A fecal coli form test is considered as most reliable test available for detesting the presence of contamination of an intesting origin, the coli form group comprises all aerobic & facuttative an aerobic, gram –ve non spirulating, rod shaped bacteria that ferment lactase with gas format within 48hrs at 35 ˚c.
- Single strength of sactose bile growth (10 ml) -10 test tube
- Double strength of sactase bile growth (10 ml) - 5 test tube
- Water sample
- Sterile pipettes
- Mac Cankey broth
- Distribute 10ml single strength lactase broth each to test tubes.
- Add 10ml of double strength lactase broth in each of test tubes.
- Introduce the Durhalm’s wial in all test tubes & sterilize them at 121˚c for 15 min.
- Inoculate 10ml of water sample to all double strength lactose broth tubes.(DSLB)
- Inoculate 1ml water sample to each of 5 SSLB tubes & 0.1ml of water sample to remaining 5 SSLB tubes.
- Incubate all the tubes at 37˚c for 24hrs.
- If gas is formed in 24hrs indicate +ve test. If no gas is formed in 24 hrs, incubate for next 24 hrs. If no gas is formed even after 48 hrs of incubation test is –ve.
- Count the no. of +ve tubes in each dilution.
- Determine the MPN by Mc Cardy’s table.