The hospital environment is particularly susceptible to contamination by bacterial pathogens that grow on surfaces in biofilms. The effects of hospital
biocides on two nosocomial pathogens,
meticillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa, growing as free-floating (planktonic) and adherent biofilm populations (sessile) were examined. Clinical isolates of MRSA and P. aeruginosa were grown as biofilms on discs of materials found in the hospital environment (
stainless steel, glass,
polyethylene and
Teflon) and treated with three commonly used hospital
biocides containing
benzalkonium chloride (1 % w/v),
chlorhexidine gluconate (4 % w/v) and
triclosan (1 % w/v). Cell viability following
biocide treatment was determined using an XTT assay and the LIVE/DEAD BacLight Bacterial Viability kit. The minimum bactericidal concentration (MBC) of all
biocides for planktonic populations of both organisms was considerably less than the concentration recommended for use by the manufacturer. However, when isolates were grown as biofilms, the
biocides were ineffective at killing bacteria at the concentrations recommended for use. Following
biocide treatment, 0-11 % of cells in MRSA biofilms survived, and up to 80 % of cells in P. aeruginosa biofilms survived. This study suggests that although
biocides may be effective against planktonic populations of bacteria, some
biocides currently used in hospitals are ineffective against nosocomial pathogens growing as biofilms attached to surfaces and fail to control this reservoir for hospital-acquired
infection.