Investigation of the efects of various stress factors on bioilms and planktonic bacteria in cooling tower model system

Abstract

Bioilm is a microbial population which live in a self-produced extracellular polymeric matrix by attaching to surfaces.Bioilms consist of diferent diferent types of organisms such as bacteria, fungi, protozoa, etc. Many bioilms that developin nature consist of more than one type of organism. Bioilms protect bacteria from adverse conditions such as temperatureluctuation and disinfectants. The aim of this study was to determine the efective elimination strategies for combating bioilmand planktonic bacteria in cooling tower model system using diferent decontamination / disinfection techniques. In thisstudy, 14 week-old bioilms were treated with temperatures of 4 °C, 65 °C; pH of 3, 11; 2 and 10 mg/l chlorine, 2 and 10 mg/lmonochloramine; hypotonic salt (0.01% NaCl) and hypertonic salt (3% NaCl) solution. For enumeration, number of aerobicheterotrophic bacteria was determined by conventional culture method, number of live bacteria was determined by LIVE/DEAD viability kit, CTC-DAPI and Alamar blue staining methods. Temperature of 65 °C, pH of 3, 10 mg/l monochloramineand hypertonic salt solution were the most efective parameters for decontamination of bioilm and planktonic bacteria. Bioilmbacteria in the circulating water system were signiicantly more resistant than planktonic bacteria against stress factors.When the numbers of epiluorescence microscopy and conventional culture technique were compared, signiicantly highernumber of live bacteria were detected using epiluorescence microscopy. Bacteria enter the viable but non-culturable phaseby loosing their culturability under stress conditions. For this reason, the conventional culture method should be supportedby diferent techniques to get more realistic numbers