Review of Coliforms - National Health and Medical Research Council

MICROBIAL INDICATORS OF DRINKING WATER QUALITY
Originally total coliform bacteria were considered to be from four genera of the family
Enterobacteriaceae that could all ferment lactose. These genera were Escherichia, Klebsiella,
Enterobacter and Citrobacter. Of the total coliforms present in the human gut, Escherichia coli
(E. coli) represents the majority of the population (see Box 2). Total coliforms represent only
about 1% of the total population of bacteria in human faeces in concentrations of about 10 9
bacteria per gram (Brenner et al., 1982).
It is widely accepted that the total coliform group of bacteria is diverse and they can be
considered normal inhabitants of many soil and water environments which have not been
impacted by faecal pollution. Even though the presence of E. coli is considered an appropriate
and specific indicator of faecal pollution, uncertainty surrounds the use of total coliforms as a
health indicator.
As microbiological understanding about the nature of disease and the pathogens responsible
increases, techniques have been developed to isolate and enumerate pathogenic viruses
and protozoa from water. These techniques, however, are not sensible, specific, reliable,
reproducible or inexpensive enough to replace the use of bacterial indicators.
2.3 ESCHERICHIA COLI (E. COLI)
More than 100 years ago scientists discovered that human faeces contained bacteria which if
present in water, indicated that the water was not safe to drink. Escherich in 1885 observed
2 types of organisms present in faeces, one of which he named Bacterium coli (B. coli, which
is now called Escherichia coli) and the concept that the presence of B. coli implied pollution
of water was readily adopted. It is recorded that the concept of “indicators” had already been
suggested in 1880 by van Fritsch based on his observations of Klebsiellae in human faeces that
were also present in water (Hendricks, 1978).
Initially it was very difficult to distinguish B. coli from other coliform bacteria in water and
faeces, so methods were developed to recover all coliform bacteria, and more detailed and
lengthy analyses were carried out to confirm if any of the recovered coliforms were B. coli.
Water bacteriologists for the next 50 years concentrated on developing these techniques to
confirm the presence of B. coli in water and tell it apart from other gut bacteria. By the turn
of the 20 th century, methods were available that could distinguish B. coli from the bacteria that
caused typhoid (Salmonella typhi), and it was known that B. coli produced acid and gas from
lactose, whereas Salmonella typhi did not. The techniques founded in the late 1800s and early
1900s are still widely used to determine if faecal pollution of drinking water has occurred.
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