Identification of strains isolated as total and fecal coliforms and comparison of both groups as indicators of fecal pollution in tropical climates

Abstract

This study was undertaken to better characterize the groups of total coliforms (TC) and fecal coliforms (FC) and to evaluate both groups as indicators of fecal contamination of drinking well water in a tropical climate (The Ivory Coast, West Africa). Isolated colonies obtained as TC or FC on membrane filters were identified using the API-20E system. From the well water samples, 58 golden-green colonies with a metallic sheen isolated on Endo medium (TC) were identified as Escherichia coli (55%), Enterobacter (26%), Klebsiella (14%), Proteus (3%) and Citrobacter (2%). Among 132 colonies isolated on Endo medium as non-TC (not showing the characteristic golden metallic sheen), 10% were identified as Escherichia coli. The 196 blue colonies isolated on M-FC medium at 44.5.degree. C (FC) were identified as E. coli (66%), Klebsiella (12%), Enterobacter (10%), Citrobacter (5%), Salmonella (3%), Serratia (3%), Proteus (2%) and Yersinia (0.5%). Among 24 nonblue colonies on M-FC medium, none were identified as Escherichia coli. Of the colonies isolated from human feces, E. coli represented 92% of the TC and 89% of the FC. Although these results are limited, they tend to confirm the greater specificity of the FC technique over that of TC for the detection of fecal contamination of untreated well water. These and previous results suggest the use of FC as the method of choice for determining drinking water pollution of untreated groundwater supplies.