Comparison of four membrane filter methods for fecal coliform enumeration

Area of Science:

• Environmental microbiology
• Water quality analysis
• Microbial enumeration techniques

Background:

• Accurate enumeration of fecal coliforms is crucial for assessing water safety.
• Existing membrane filter methods have limitations in accuracy, specificity, and recovery.

Purpose of the Study:

• To evaluate and compare four membrane filter methods for fecal coliform enumeration.
• To determine the accuracy, specificity, upper counting limit, and recovery comparability of each method.

Main Methods:

• Evaluation of m-FC, mTEC, m-FC2, and MacConkey membrane broth methods across six laboratories.
• Assessment of recovery accuracy with pure cultures and temperature-stressed cultures.
• Specificity testing through colony verification and analysis of false positives/negatives.
• Counting range experiments and recovery comparisons using diverse water samples.

Main Results:

• mTEC, m-FC, and m-FC2 methods showed high recovery (89-100%) with pure cultures, while MacConkey was <60%.
• Recovery decreased significantly under temperature stress (10°C).
• mTEC exhibited the highest upper counting limit (130 colonies/filter) and superior recovery from chlorinated effluents.
• m-FC2 had the highest false-positive rate (18%), and MacConkey had the highest false-negative rate (26%).

Conclusions:

• The mTEC method provides the best overall performance for fecal coliform enumeration.
• mTEC offers high recovery, low background colonies, good specificity, accuracy, and a high upper counting limit.
• mTEC allows for the enumeration of Escherichia coli within 24 hours, enhancing efficiency.