Microbiological assessment of biofilm in drinking water distribution system of Kathmandu.

Thesis Report.

ABSTRACT: Biofilm exist ubiquitously in drinking water distribution systems. Biofilm growth within a water distribution system could lead to operational problems such as pipe corrosion, water quality deterioration and other undesirable impacts in water distribution systems. The aim of the study was to describe physico-chemical and microbiological status of drinking water and to asses total bacterial load and presence of gram negative bacteria in biofilm in pipeline of drinking water and to determine the antibiotics susceptibility of the isolates. This study was conducted in Research Laboratory of Nepal Academy of Science and Technology (NAST), Khumaltar, Lalitpur. A stratified random sampling was adopted to collect total of 114 each of biofilm and water samples in Kathmandu from 4 distribution points namely Balaju (20), Basbari (34), Minbhawan (40) and Tikabhairab (20) distribution point. The samples were also distributed on the basis of distance from the distribution points (Far=57, Near=57) and type of pipeline (Metal=62, Polymeric=52). Observation checklist and brief interview with owner was recorded in order to collect information related to type of pipeline, distance and time of pipe installation. In physico-chemical parameters temperature by digital thermometer, conductivity by conductivity meter, turbidity by nephalometer and free, combined and total residual chlorine by DPD colorimetric method were measured, whereas in microbiological analysis of water Total coliforms by Membrane filteration method, thermotolerant colifilms Brillant Green Lactose Bile broth and Escherichia coli were enumerated. In both the biofilm and water samples Hetertropic plate count (HPC) by spread plate agar method and Gram negative enteric bacteria by using selective media and biotyping were conducted. Antibiotics susceptibility test was conducted for 36 isolates of biofilms and 38 isolates of water against 12 different antibiotics by Standard disk diffusion method. The average temperature, turbidity, conductivity of the 114 Water samples were found to be 17.51oC, 2.46 at 4 NTU, 114.71µS/cm. In terms turbidity 20.2% of the sample crossed the permissible guideline value of WHO and also national standard. The average free residual chlorine, combined residual chlorine and total residual chlorine was found 0.24mg/L, 0.04mg/L and 0.28 mg/L respectively. Total coliform were found in 61.4% (70/114) of water samples among which 15.7% (11/70) were found to be thermotolerant coliform. In distance, coliforms were found higher in far points (p=0.002). All thermotolerant coliform isolates were found to be E. coli. Mean HPC of water was found log103.15 whereas mean HPC of biofilm was found log104.95. The mean HPC of water (p=0.003) and Biofilm (p=0.001) was found higher in far point. Significant difference was found in HPC of drinking water (p=0.024) to distribution point. From water sample 10 different enteric bacteria were isolated in which E. coli was found most predominant followed by Pseudomonas spp., Citrobacter spp., Klebsiella spp., Shigella spp., Proteus spp., Enterobacter spp. Non-Typhi Salmonella spp., Providencia spp., Edwardsiella spp. In biofilm samples, Pseudomonas spp. was found most predominant followed by Escherichia coli, Enterobacter spp., Klebsiella spp., Citrobacter spp., Proteus spp. and Providencia spp. No Salmonella spp., Shigella spp. and Vibrio spp. were detected in the biofilm. In antibiotics susceptibility test, biofilm isolates were found to be more resistant to Ampicillin (92%), in water isolates the resistance was found high against Ampicillin (88.5%). Multiple antibiotics resistance was found higher in biofilm isolates (86.1%) than in water isolates (39.5%). Heterotrophic plate count in biofilm and in water was found higher at far points. Enteric bacteria were found associated in biofilms. More multiple antibiotics resistant bacteria were isolated from biofilms. Keywords: biofilm, distribution system, drinking water, pathogen

Eng.