Experiment 5 - Determination of Coliforms In Water By The Most-Probable-Number Method (MPN Test)

How is the sanitary quality of drinking (potable) water determined?

By the kinds of microorganisms present rather than by the number

What types of water is considered potable?

Streams, springs, wells, rivers, ponds, and lakes which contains a multitude of microorganisms

What does it mean to be considered potable?

As long as human pathogens are absent

What origin are many pathogens?

Fecal origins

How are microorganisms of fecal origins introduced into potable waters?

Via sewage pollution, as they can be guarded against if sewage is detected by a bacteriological tests.

What do sewage contain

Coliform bacteria

Why are coliform bacteria used as the indicator?

Sewage always contains them in large numbers and can be detected more easily and quickly that most pathogens.

What do coliforms indicate since they are nonpathogenic?

The presence of fecal matter, not necessarily that of harmful microorganisms.

What are the three tests for the analysis of potable water?

1. Presumptive

2. Confirmed

3. Completed

What does the presumptive test consist of?

Inoculating a sample into multiple lauryl tryptose broth tubes

How is the water assumed/presumed to be contaminated with fecal materials and unsafe to drink in the presumptive test?

If the lauryl tryptose broth is fermented with production of gas

Is a positive result from the presumptive test caused by coliforms?

Occasionally, but mostly by a species of the genera Clostridium or Bacillus