Underestimation of total-coliform counts by the membrane filter verification procedure

Area of Science:

• Microbiology
• Water Quality Testing
• Bacteriology

Background:

• Coliform bacteria are key indicators of water contamination.
• Standardized testing methods are crucial for accurate water quality assessment.
• Citrobacter freundii has been identified as a potential source of false-negative results in coliform testing.

Purpose of the Study:

• To investigate the cause of false-negative results in total-coliform membrane filtration tests.
• To identify the specific factors contributing to the failure of Citrobacter freundii detection.
• To understand the role of media composition in coliform verification.

Main Methods:

• Comparison of Citrobacter freundii growth and gas production in lauryl tryptose broth and brilliant green bile broth.
• Analysis of the impact of different peptone sources on bacterial response.
• Evaluation of the total-coliform membrane filtration test protocol.

Main Results:

• Citrobacter freundii produced gas in brilliant green bile broth but not in lauryl tryptose broth.
• Negative verification results were observed in the total-coliform membrane filtration test.
• The observed discrepancies were attributed to variations in the peptone components of the culture media.

Conclusions:

• The peptone source in microbiological media significantly influences the detection of certain coliforms, like Citrobacter freundii.
• Standard membrane filtration tests may require media adjustments to accurately identify all coliforms.
• Further research into media formulation is needed for reliable water quality monitoring.