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The optimization and application of two direct viable count methods for bacteria in distributed drinking water
J Coallier1, M Prévost, A Rompré
1Ecole Polytechnique de Montréal, Department of Civil Engineering, Environment, QC, Canada.
Canadian Journal of Microbiology
|October 1, 1994
Summary
The direct viable count method using nalidixic acid requires standard incubation. However, the 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) method offers higher bacterial counts in drinking water samples.
Area of Science:
- Microbiology
- Water Quality Analysis
- Bacteriology
Background:
- Direct viable count (DVC) methods are crucial for assessing viable bacteria in environmental samples.
- Standard DVC methods often require specific incubation conditions that may not be optimal for all bacterial populations.
- Nalidixic acid and 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) are commonly used viability stains.
Purpose of the Study:
- To determine optimal incubation conditions for the nalidixic acid DVC method.
- To evaluate the efficacy of the CTC DVC method under in situ conditions for drinking water bacteria.
- To compare bacterial counts obtained by nalidixic acid and CTC DVC methods in mixed bacterial populations.
Main Methods:
- Optimal incubation conditions for nalidixic acid DVC were determined for laboratory and mixed bacterial populations.
- In situ DVC using CTC (1 mM, 4-6 h, pipe temperature, no exogenous substrate) was applied to drinking water samples.
- Results from both methods were compared for a laboratory strain and a mixed bacterial population.
Main Results:
- Optimal incubation conditions for nalidixic acid DVC were consistent with existing literature.
- For a laboratory strain, both nalidixic acid and CTC methods yielded similar results.
- The CTC method consistently yielded higher bacterial counts than the nalidixic acid method for mixed bacterial populations from drinking water.
Conclusions:
- Standard incubation conditions are suitable for the nalidixic acid DVC method in drinking water microbiology.
- The CTC DVC method is a viable alternative for assessing viable bacteria in drinking water.
- The CTC method may be more sensitive than the nalidixic acid method for enumerating viable bacteria in complex environmental samples like drinking water.