Feasibility of disinfection kinetics and minimum inhibitory concentration determination on bacterial cultures using flow cytometry

Disinfection kinetics has been well established for selected antimicrobial agents on isolated bacterial strains. Due to the difficulties of culturing most bacteria, the majority of these studies have been limited to readily cultivable microorganisms of a single type or family. This study explores the feasibility of using flow cytometry for characterising the disinfection kinetics and minimum inhibitory concentration (MIC) of an Escherichia coli culture and a microbial consortium. The proposed method relies on fluorescent dye molecules to indicate the morphological and physio-logical status of numerous individual cells. Biocides of varying effectiveness and inactivation mechanisms (chlorine, iodine, and silver) were used to evaluate this novel application. Using pseudo-first-order kinetics, the coefficients of specific lethality of chlorine and iodine on Escherichia coli were 4.71 and 3.78 x 10(-3) L mg(-1) min(-1) and MIC of silver ion was between 60 and 80 mu g L-1. The coefficients of specific lethality of chlorine and iodine on the microbial consortium were 4.96 and 8.89 x 10(-3)L mg(-1) min(-1) and min(-1) of silver ion was between 40 and 60 mu g L-1. This method can be used to provide a rapid and consistent way of determining disinfection kinetics and MICs for pure and mixed bacterial cultures and can potentially be used to examine water and wastewater disinfection efficiency. However, caution should be used to ensure that the physiological and morphological status characterised by cytodyes is a result of the inactivation mechanisms of the disinfectants evaluated.