The Differential Effect of Temperature on Gas Production by a Coliform Organism

SUMMARY: The influence of the temperature of incubation on the course of formic acid and gas production by cultures of a coliform organism growing in buffered and unbuffered peptone media was studied. The evidence suggests that at 30 ' and at 87 ' the onset of gas production is determined by the concentration of undissociated formic acid in the culture, but that a higher concentration of acid is required to elicit response at 87 ' than at 30". Undissociated formic acid is toxic to the organism and it appears that gas is not produced in unbuffered glucose medium at 3'7 " because the environmental conditions do not allow elaboration of hydrogenlyase before inhibitory conditions of pH value and formate concentration are attained. Coliform bacteria which ferment sugars at 37 ' with the production of acid and gas are believed to be mainly of intestinal origin and their presence in water is considered indicative of faecal contamination. In routine water analysis occasional coliform strains are encountered which ferment sugars at 37 " with-out the production of gas but which produce acid and gas in the normal way at lower temperatures (Prescott, Winslow & McCrady, 1946). These strains ar