EFFECT OF OXIDASE POSITIVE BACTERIA ON TOTAL COLIFORM DENSITY ESTIMATES

Abstract

The most probable number method for enumerating coliforms apparently gave a false estimate of coliform density. Inflated estimates were due to lactose positive, non-coliform bacteria whose presence was detected by an oxidase test. Of all samples examined, 38% contained oxidase positive bacteria that were able to produce gas from lactose. Their presence resulted in coliform density overestimates which ranged from 2-33 times the true value. Frequency of occurrence of inaccurate estimates apparently was affected by water temperature but unrelated to environmental source.