Enumeration and identification of heterotrophic bacteria in groundwater and in a mountain stream

Populations of heterotrophic bacteria were enumerated from stream and groundwater samples taken from an undisturbed catchment basin in southwestern Alberta. Direct counts using epifluorescence microscopy were compared with total viable counts using standard plate count methods, the iodonitrotetrazolium formazan method (reduction of 2-(p-iodophenyl)-3-(p-nitro phenyl)-5-phenyl tetrazolium chloride to iodonitrotetrazolium formazan), the nalidixic acid method, and the slide culture method. The nalidixic acid method gave the highest results, with total viable counts as high as 34.6% of the total direct count. Attempts to enumerate bacteria on media made from decaying leaves and algal–bacterial slime gave lower values, approximately 10% of the numbers obtained on enriched media. Stream waters were found to be dominated by Pseudomonas spp. and groundwaters were dominated by Bacillus spp. No differences were found in either numbers or species identified between tryptone – glucose – yeast extract agar, brain–heart infusion agar, nutrient agar, or casein–peptone–starch agar.