what is an alternative method to MPN method for determining faecal coliform concentration in water samples using a reference

An alternative method to the Most Probable Number (MPN) method for determining fecal coliform concentration in water samples is the Membrane Filtration (MF) Method.

Overview of the Membrane Filtration Method

1. Principle: The MF method involves filtering a measured volume of water through a membrane filter with a pore size that retains bacteria. After filtration, the filter is placed on a selective agar medium that supports the growth of fecal coliforms while inhibiting non-fecal coliforms.

2. Procedure:

   • Sample Collection: Collect water samples in sterile containers.
   • Filtration: Pass a known volume (often 100 mL) of the water sample through a sterile membrane filter.
   • Incubation: Place the filter on a selective agar medium (like mFC agar or similar) and incubate at the appropriate temperature (typically 44.5°C for fecal coliforms).
   • Colony Counting: After incubation, count the number of colonies that develop on the filter. Each colony represents a fecal coliform bacterium.

3. Calculations:

   • The concentration of fecal coliforms in the original water sample can be calculated using the formula: $\text{Concentration} = \frac{\text{Number of Colonies} \times \text{Dilution Factor}}{\text{Volume Filtered (mL)}}$

Reference

For a comprehensive understanding of the MF method and its application, refer to:

• American Public Health Association (APHA) Standard Methods for the Examination of Water and Wastewater.

This alternative method is often preferred for its efficiency and ability to provide quantitative results rapidly.