Evaluation of simple microbiol tests for detection of fecal coliforms directly at 44.5 degrees C

Simple microbial test comprising H2S paper strip test, presence-absence (PA) test, and fluorogenic brila broth (BB) test performed directly at 44.5 degrees C were evaluated and compared with the standard most probable number (MPN) method for detection of fecal coliforms in 173 drinking water sources. BB and PA test were comparable with standard MPN method, whereas, poor compliance was noted for H2S test. PA test when compared with standard MPN test only 15% disagreement was detected, whereas, highest disagreement of 40% was observed in case of H2S test. BB test was found to be highly sensitive as only 7.8% disagreement with that of standard MPN test was found. Three hundred cultures obtained from positive tests were identified in order to evaluate the specificities of test used in detection of fecal indicator Escherichia coli. BB test was also found highly specific in detection of indicator organism as compared to PA and H2S test. Among the organisms isolated from BB test 84.4% of them were identified as E. coli as compared to 43.4 and 33.3 in PA and H2S test, respectively. The low incidence of recovery of E. coli (18.1%) for the standard MPN method places doubt on the validity of its application in tropical areas. The result of this investigation suggest that BB performed directly at 44.5 degrees C could be suitable cost effective test to assess the microbiological quality of drinking water in India and other tropical countries.