In addition to expressing β-D-galactosidase,coliform bacteria are Gram-negative non-sporeforming, oxidase-negative, rod-shaped bacteria, which are capable of aerobic and facultative anaerobic growth in the presence of bile-salts (or other surface-active agents with similar growth-inhibiting properties) and which are normally able to ferment lactose with the production of acid and aldehyde within 48 h when incubated at a temperature of (36+-2)c