BIOFILM PARAMETERS INFLUENCING BIOCIDE EFFICACY

The influence of biofilm areal cell density, species composition, and the presence of abiotic particles on the disinfection and removal of b acterial biofilms by monochloramine was investigated. Mono- and binary population biofilms of Pseudomonas aeruginosa and Klebsiella pneumoni ae were grown on stainless-steel slides in a continuous flow annular r eactor. Biofilms were treated in the reactor with a pulse/step dose of 4 mg/L monochloramine for 2 h. Biofilm samples were disaggregated and assayed for colony formation on R2A agar and for total cell numbers b y acridine orange direct counts. These data were used to determine app arent first order rate coefficients for the processes of disinfection and detachment. Disinfection rate coefficients exceeded detachment rat e coefficients by as much as an order of magnitude and the two coeffic ients were poorly correlated (r = 0.272). The overall decay rate coeff icient (disinfection plus detachment) depended strongly on the initial biofilm areal cell density. It displayed a parabolic dependence on ce ll density with a maximum near 10(8) cfu/cm(2). This result points to multiple factors influencing biofilm susceptibility to antimicrobial c hallenge. Decay rates of K. pneumoniae measured in binary population b iofilms were comparable with those measured in monopopulation biofilms (p = 0.61). P. aeruginosa decayed more slowly in biofilms dominated b y K. pneumoniae (p 0.028), indicating some interaction between species , The presence of kaolin and calcium carbonate particles in the biofil m reduced disinfection efficacy. (C) 1995 John Wiley & Sons, Inc.