Bacteriological methods for distinguishing between human and animal faecal pollution of water: results of fieldwork in Nigeria and Zimbabwe.

Bacteriological techniques have traditionally been used to detect faecal pollution of drinking water supplies. Recently, methods have been developed to distinguish between human and animal faecal pollution in temperate climates. The present study assessed the applicability and practicality of these methods in tropical countries. Fieldwork in Nigeria and Zimbabwe has shown that animal faecal pollution can reliably be identified by the detection and enumeration of Rhodococcus coprophilus using modified M3 agar, whereas human faecal contamination can be identified by the detection of sorbitol-fermenting bifidobacteria. Each of these organisms was detected only in the faeces of the type (human or animal) that it was meant to indicate. Although Streptococcus bovis has been used in the past in mainly temperate countries to distinguish animal from human faecal contamination, the present study has shown that this organism is not a reliable indicator of animal pollution in the tropics because it was excreted by a proportion of the human population in both Nigeria and Zimbabwe. Water sources known to be contaminated by human or animal excreta were examined for these indicator organisms. The results correlated with the results obtained from examining human and animal faecal specimens for these organisms. The role of these bacteriological methods in water pollution control programmes is discussed.