Enterococci vs coliforms as a possible fecal contamination indicator: Baseline data for Karachi

ABSTRACT

Fecal contamination of drinking water is the major cause of water borne illnesses. For long time coliforms are exploited as fecal contamination indicator. However, recent studies indicate low survival rate of coliforms in stress conditions, hence it's use as indicator of fecal pollution is being abandoned in many parts of the developed world. Implementation of such strategy demands availability of local data in the cities like Karachi. The present study provides a comparison between coliforms and enterococcal load and its variation in sewage samples collected [June, August and November, 2006] from eighteen towns of Karachi. All the diluted samples were selective media to obtain colony-forming units [CFU] mainly for coliforms and enterococci. The bacteria isolated were identified on the basis of conventional microbiological methods. Observations thus obtained were subjected to rigorous statistical analysis. The total load of enterococci was found in range of 1.27-8.47 X 107 as compared to coliforms [3.03-13.9 X 107]. However, segregation of data reveals greater inter town variability in CFU/ml both in coliforms and enterococci as suggested by their cumulative standard deviation +1.5 X107. Furthermore, CFU/ml of both coliforms and enterococci also varies to variable scale when collected at different time intervals and at intra town level. Conclusively, the studies suggest high survival rate and lower variability of Enterococci compared to escherichia hence indicating its potential advantage to be used as fecal contamination indicator