EFFECT OF THE GROWTH-RATE OF PSEUDOMONAS-AERUGINOSA BIOFILMS ON THE SUSCEPTIBILITY TO ANTIMICROBIAL AGENTS

The growth rate of biofilm cells of a leucine-requiring mutant Pseudom onas aeruginosa HU1 was regulated by the leucine concentration in the chemically defined medium, and the effect of the growth rate of biofil m cells on the antimicrobial activities of the antimicrobial agents pi peracillin (PIPC), imipenem (IPM) and ofloxacin (OFLX) were evaluated. PIPC showed little effect on the biofilm bacteria regardless of the l eucine concentration in the medium. IPM showed weak bactericidal activ ity to biofilm cells; activity was greater in younger biofilm cells gr owing in high concentrations of leucine. On the other hand, OFLX revea led strong bactericidal activity to biofilm bacteria regardless of the growth rate. Our data suggest that the bactericidal action of antimic robial agents to biofilm bacteria is different from that to planktonic bacteria. The bioassay using mutants with regulated growth is useful for the evaluation of the efficacy of antimicrobial agents against bio film bacteria.