PHYSIOLOGICAL-RESPONSES OF BACTERIA IN BIOFILMS TO DISINFECTION

In situ enumeration methods using fluorescent probes and a radioisotop e labelling technique were applied to evaluate physiological changes o f Klebsiella pneumoniae within biofilms after disinfection treatment. Chlorine (0.25 mg of free chlorine per liter [pH 7.2]) and monochloram ine (1 mg/liter [pH 9.0]) were employed as disinfectants in the study. Two fluorogenic compounds, 5-cyano-2,3-ditolyl tetrazolium chloride a nd rhodamine 123, and tritiated uridine incorporation were chosen for assessment of physiological activities. Results obtained by these meth ods were compared with those from the plate count and direct viable co unt methods. 5-Cyano-2,3-ditolyl tetrazolium chloride is an indicator of bacterial respiratory activity, rhodamine 123 is incorporated into bacteria in response to transmembrane potential, and the incorporation of uridine represents the global RNA turnover rate. The results acqui red by these methods following disinfection exposure showed a range of responses and suggested different physiological reactions in biofilms exposed to chlorine and monochloramine. The direct viable count respo nse and respiratory activity mere affected more by disinfection than w ere the transmembrane potential and RNA turnover rate on the basis of comparable efficiency as evaluated by plate count enumeration. Informa tion revealed by these approaches can provide different physiological insights that may be used in evaluating the efficacy of biofilm disinf ection.