Isolation of Free Living Amoebas as a Highly Sensitive Index of Water Contamination

Abstract

Safe drinking water is a rare commodity in India. Several water borne diseases are commonly reported from metropolitan cities of India, most likely due to unsatisfactory disinfection of municipal water. The analysis of the microbiological flora of the water supplied for drinking purposes shows that New Delhi water is biologically contaminated. Six hundred water samples obtained from New Delhi residential complexes included 96 from direct taps, 310 from overhead tanks used for storing the same water for urgent needs, and 194 were from water filter residues. The samples were repeatedly collected in every season for two consecutive years. Ninety percent of the water samples were found to be biologically contaminated. Most contaminated samples were from overhead water tanks (97.4 percent) and from filter residues (94.5 percent). Even direct tap water was found to be contaminated in more than 50 percent of the samples. The most common isolates were from the protozoan category, the free living amoeba (90.1 percent) and by aerobic bacteria (73.0 percent). Overhead tank water samples were co-contaminated with as many as 15 microorganisms. Isolation of free living amoebae was found to be the most sensitive tool of analyzing the water safety. It is proposed that after determining the microbiological contamination, the public health laboratories should modify the existing technique and must perform the cultures for free living amoebae on non-nutrient agar in addition to the standard coliform test.