Experiment 6: Determination of Coliform Numbers in Water by the Membrane Filter Technique

What are total coliforms?

• ferment lactose

• produce acid and gas

• form green sheen colonies

on membrane filterrs using Endo broth

What are fexal coliforms?

• grow and ferment lactose

• produce acid and gas

• blue colonies on membrane fikters using m-FC broth.

Which is more indicative of fexal contamination total or fexal coliforms?

Fexal Coliform

bc total coliforms could come from other sources.

What is endo broth?

• selective media

• sodium desoxycholate and sodium lauryl sulfate used to inhibit growth of gram positives

• has lactose for coliforms to ferment

• breaks down lactose which releases aldehydes which basic fuchsin dye reacts with.

  • creates shiny green coating; only count these.

What is m-FC basal media?

• count fexal coliforms

• BCIG in the media turns the colonies blue when it is cleaved by B-glucuronidase (enzyme made by e.coli)

• tryptose, proteose peptone and yeast extract = C, N, VitB + nutrients

• Bile salts inhibit gram positive organims

What are some advantages of Membrane filter method?

• Greater sensitivity

• Larger sample volumes can be tested

• Results are more reproducible

• Short experimental time

What are some disadvantages of Membrane filter method?

• Water sample must be processed before hand to remove extraneous material that may clog the filter.