Chlorine resistant bacteria isolated from drinking water treatment plants in West Bengal

Resistance to different concentrations of chlorine have become a major problem in some areas of West Bengal. The study involves surveillance of different drinking water treatment plants located in West Bengal for the isolation of chlorine resistant bacteria as contaminants. The risk assessment studies involved extensive microbiological work based on isolation and enumeration of pathogens through membrane filter technique, identification of isolates based on their morphological characteristics and enumeration of chlorine resistant bacteria from drinking water treatment plants. The chlorine content of water was measured at the time of plating. All the water systems maintained more or less 1 mg/ L residual free chlorine despite of that many species like Staphylococcus aureus, Klebsiella, Pseudomonas and Clostrdial were isolated from these water systems. The experimental result states that the Gram positive bacteria were more resistant to chlorination than Gram negatives. WTP-IV was more at risk where E. coli was isolated at a sub-optimal dosage of chlorine, 0.5 mg/L. All the isolates survived except E. coli and Serratia at 2 mg/L chlorine for 30 min. The results suggests emergence of chlorine resistant pathogens from chlorinated water supply systems of West Bengal. The experimental results implies on employment of effective preventive measures keeping in view the emergence of chlorine resistant forms and demands formulation of new strategy in the upcoming revised Standard operating procedures for safe drinking water which must be adopted by water systems, most vulnerable to chlorine treatment.