Evaluation of factors affecting the membrane filter technique for testing drinking water

Area of Science:

• Environmental microbiology
• Water quality analysis
• Microbial detection techniques

Background:

• The membrane filter (MF) technique is increasingly adopted for drinking water testing.
• Questions arose regarding its efficacy and optimal use compared to traditional methods.
• Standardization of MF technique protocols is crucial for reliable water quality monitoring.

Purpose of the Study:

• To compare the MF technique with the most-probable-number (MPN) method for total coliform recovery.
• To optimize medium preparation, storage, and verification procedures for the MF technique.
• To investigate atypical colony morphology and develop strategies for handling overgrown cultures.

Main Methods:

• Comparative analysis of MF and MPN techniques using m-Endo agar LES.
• Studies on medium rehydration, light exposure, and storage stability.
• Evaluation of different broth verification methods (lauryl tryptose and brilliant green bile).
• Investigation of atypical colony characteristics and overgrowth phenomena.

Main Results:

• MF technique with m-Endo agar LES demonstrated superior coliform recovery over MPN methods.
• Optimal conditions for m-Endo agar LES preparation and storage were established.
• Parallel inoculation of lauryl tryptose and brilliant green bile broths proved more effective than sequential methods.
• Direct inoculation of brilliant green bile broth using a swab from overgrown MF plates yielded the best results.

Conclusions:

• The MF technique is a reliable and effective method for total coliform detection in drinking water.
• Optimized protocols enhance the accuracy and efficiency of the MF technique.
• Modified verification and overgrowth handling procedures improve coliform recovery rates, even with extended sample holding times up to 72 hours.