IRREGULARITIES IN THE TEST FOR B. COLI IN WATER

Abstract

Observations and results of experiments on the problem of non-confirming presumptive positive B. coli tests at Toronto, Canada, are given. Failures are of 2 types: (1) those probably due to presence of aerobic or anaerobic spore-forming lactose-fermenting bacteria or gas-producing symbiotic complexes, and (2) those in which colon-group bacteria were originally present but were lost in the confirmatory procedure. The latter are discussed. Typical examples of results obtained when pollution was known to exist are quoted, in which the indicated concentration of B. coli would have been 100- to 100,000-fold greater if losses had not occurred. These failures are believed to be due to production of an inhibiting ph during preliminary enrichment. It is pointed out that while it is generally known that B. coli is inhibited by acidity formed by its own growth in carbohydrate media, this fact does not seem to have been seriously considered as a factor in the failure of presumptive tests.