Total coliform bacteria
General description
Total coliform bacteria include a wide range of aerobic and facultatively anaerobic, Gram-negative, non-spore-forming bacilli capable of growing in the presence ofrelative high concentrations of bile salts with the fermentation of lactose and production of acid or aldehyde within 24 hours at 35–37 °C. Escherichia coli and thermotolerant coliforms are a subset of the total coliform group that can ferment lactose at higher temperatures (see below). As part of lactose fermentation, total coliforms produce the enzyme β-galactosidase. Traditionally, coliform bacteria were regarded as belonging to the genera Escherichia, Citrobacter, Klebsiella and Enterobacter, but the group is more heterogeneous and includes a wider range of genera, such as Serratia and Hafnia. The total coliform group includes both faecal and environmental species.