Discuss the methods of detection of E. Coli.

Question

08 Jul 2022

Answer :

Word Count : 1176

METHODS OF DETECTION OF E.COLI ARE -

1 Most Probable Number (MPN) method

a) Presumptive test for detection of coliforms, fecal coliforms and E. coli

1. Weigh 50 g of sample in a sterile jar and add 450 ml of Butterfield's phosphate-buffered water. Blend it for 2 min. This gives a 10-1 dilution.

2. Prepare decimal dilutions from first dilution.

3. Mix the dilutions by shaking the bottles or by vortexing.

4. Transfer 1ml of dilution to 3 tubes of LST broth each for 3 consecutive dilutions. Transfer 1 ml dilution to 5 LST tubes if analyzing shellfish and shellfish harvest waters.

5. Incubate all tubes at 35oC for 48 h and look for gas production after 24 h and 48 h of incubation.

6. Use tubes showing positive reaction for gas production for MPN confirmed tests.

b) Confirmed test for coliforms

Inoculate a loopful of inoculum from positive (Gassing) LST tubes to BGLB broth and incubate them at 35oC for 48 h. Examine the tubes for gas production and calculate MPN of coliforms based on proportion of confirmed gassing LST tubes for 3 consecutive dilutions.

c) Confirmed test for E. coli and fecal coliforms

Inoculate a loopful from the positive LST tubes (presumptive test) to EC broth. Incubate these tubes at 45.5oC (44.5oC if analyzing shellfish) for 48 h. Observe for gas production and calculate MPN for fecal coliforms.

d) MPN – Completed test for E. coli

1. Streak a loopful of culture from EC tube (positive for gas) on L-EMB agar and incubate the plates at 35oC for 24 h.

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