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.