EFFICIENCY OF MODIFIED H_2S TEST FOR DETECTION OF FAECAL CONTAMINATION IN WATER

摘要

Faecal contamination is a major causative factor for incidence of water borne infectious diseases. Certain hydrogen sulfide (H_2S) producing enteric bacteria such as Salmonella sp. and Cit-robacter sp., assosiated with coliforms, have been considered for rapid detection of recent faecal contamination in water. The basic H_2S test medium, modified by adding 0.25 gm/L of L-cystine HCl, was examined for its efficiency with 90 water samples collected from 40 pipe supplies, 20 open wells, 15 hand pumps and 15 different surface water bodies (river, streams and ponds). Sterilized modified culture medium in glass vials was inoculated with 100 mL of each sample and incubated at 20, 25, 30, 35 and 44℃ for 18, 24,42,48, 66 and 72 h. Blackening of content in incubated vials was considered positive. For comparison, most probable number (MPN) of coliform and faecal coliform per 100 mL was also estimated in each sample by multiple tube fermentation (MTF) method. H_2S positive result was exhibited by 78% of samples. Coliform ( > 10) and faecal coliform/100 mL were also detected in 59% of samples. Maximum H_2S positive results (100%) were found with well and surface water samples incubated at 30, 35 and 44℃ for 18 h. Coliform ( > 10) and faecal coliform/100 mL were also detected in most of these samples. Pipe supplies (60%) and hand pumps (73%) also exhibited considerable H_2S production. Coliforms and faecal coliforms were also found in significant number of these samples. Thus, the modified H_2S test may prove a useful alternative indicator of faecal con-tamination for water quality surveillance and screening of large number of water samples in short duration, particularly during any outbreak of water borne disease among rural population.