Correlations of Aeromonas hydrophila with Indicator Bacteria of Water Quality and Environmental Factors in a Mountain Stream

The occurrence of Aeromonas hydrophila in a mountain stream was studied quarterly for more than 3 years. A. hydrophila and fecal coliforms were measured by the membrane filter method, and heterotrophic plate counts (HPC) were measured by the pour plate method at 20 and 35 °C. A. hydrophila was detected from all samples collected and correlated with HPC, especially at 35 °C, but not with fecal coliforms. A. hydrophila densities along the main stream in a log scale correlated positively with the catchment areas in a log scale. The intercepts of the regression lines correlated positively with the mean water temperatures along the channel, which is considered to reflect the growth of the bacterium on the stream bed. The slopes correlated negatively with total precipitation in a 60‐day period before each sampling. These results suggested that the factors controlling A. hydrophila in a mountain stream were water temperature and precipitation, and that the bacterium was indigenous to stream environment rather than from contamination because of human activity.