VPE 511: Environment and Environmental Hygiene (2+1)

COLIFORM BACILLI

• The coliform bacilli constitute a group of organisms of diverse origin. Whose natural habitat is the human and animal intestine and named as Escherichia coli.
• Some of the coliform groups appear to have their primary habitat in the soil and on vegetation and may, therefore, be regarded as saprophytes; these comprise the E.aerogenes, and E cloacae.
• The typical E. coli does not normally lead a saprophytic existence outside the human and animal intestine.
• It is the dominant organism found in faeces, and for this reason is commonly referred to as “ faecal coli,” whilst the saprophytes referred to as “non-faecal coli”.
• The observations of various workers suggest that at ordinary temperatures non faecal coli group tend to survive longer in water than do faecal coli, through factors other than temperature probably play a part in determining the relative length of survival of these organisms.
• Since E coli does not normally live for any length of time outside the intestinal tract of man and animals , the presence of this organism in water can be regarded as almost certain evidence of recent excretal pollution of human or animal origin.
• The further significance of the coliform group as an indication of the nature and time of pollution will be returned to later.
• It may be mentioned here, however, that there is no very satisfactory method at present for distinguishing between faecal coil of human origin on the one hand and those of animal origin on the other.
• A consideration of the topographical circumstances relevant to the water supply under examination may sometimes help in assigning faecal coli to their probable source.
• For example , in the case of surface waters where sheep commonly graze the gathering grounds , and in the absence of any known sources of human pollution, the faecal coli isolated from samples are in all probability of animal origin.
• A similar conclusion may sometimes be arrived at in the interpretation of the bacteriological findings in the case of a well or stream water, where the topographical survey on the spot indicates excretal pollution by livestock and, as far as can be seen after careful investigation, there is little possibility of contamination from human sources.