Abstract
Applicability of a new simple method for estimating heterotrophic plate count (HPC) in environmental samples was investigated. In this method, 0.1-1.0 ml of sample is incubated in a cell equipped with a dissolved oxygen (DO) electrode. The HPC in the sample is estimated from the time required until the DO is depleted (detection time). This method was applied to a pure culture sample and environmental samples to evaluate the validity and reliability of this method.
The results indicated that (1) the HPC estimated by this method was in agreement with that determined by the plate count method in environmental samples (r = 0.85), (2) 95 % confidence interval of detection time of this method was shorter than the generation time of bacteria in the samples with HPCs higher than 102-103 CFU·ml-1, (3) In the case in which the same amounts of heterotrophic bacteria existed in the sample cell, the detection time (mean value and 95 % confidence interval) for bacteria captured on a polycarbonate membrane filter (0.2 μ m) was comparable with that for bacteria suspended in the sample cell.
Thus, it could be concluded that this simple method could more rapidly estimate the HPC in environmental samples than the conventional plate count method with comparable accuracy and could be sufficiently applied to low-HPC samples.
