Evaluation of the activity of disinfectants against coliform bacteria group strains isolated from a sewage treatment plant (ETE-Ipanema)

Abstract

Municipal waste water usually presents pathogenic enteric bacteria, viruses and intestinal parasites. Primary, secondary and tertiary waste water treatments eliminate 90-99.9% of these microorganisms and if a more efficient reduction of microorganisms is needed, disinfection using chemical compounds is be done. The extraordinary genetic variability of bacteria gives them the ability to adapt against these chemical agents which with indiscriminate use brings about serious health problems. This study was conducted to investigate the efficacy of the different chemical agents commonly used in disinfection procedures like chlorhexidine gluconate, sodium hypochlorite and quaternary ammonium compounds against coliform bacteria isolated from a sewage treatment plant using the macrodilution method. It was observed that the addition of organic matter interfered with the sensitivity levels and also the lower the concentration and the exposure time, the higher the resistance. Sodium hypochlorite was most effective against the coliforms, which inhibited bacterial growth in every exposure time and concentration used. Quaternary ammonium compounds and chlorhexidine gluconate were also effective, although a higher percentage of resistance was observed for both. For surfaces and skin disinfection, chlorhexidine gluconate and ammonium quaternary compounds can be used to reduce the number of coliform bacteria. It is suggested that a higher concentration of the chemical agents be used to ensure total disinfectant efficacy and reduced the resistant strains.