Effect of chlorhexidine and benzalkonium chloride on bacterial biofilm formation

To study the effect of antiseptics on bacterial biofilm formation. Biofilm formation and planktonic growth were tested in microtiter plates in the presence of antiseptics. For Escherichia coli G1473 in the presence of chlorhexidine or benzalkonium chloride, for Klebsiella pneumoniae CF504 in the presence of chlorhexidine and for Pseudomonas aeruginosa PAO1 in the presence of benzalkonium chloride, biofilm development and planktonic growth were affected at the same concentrations of antiseptics. For PAO1 in the presence of chlorhexidine and CF504 in the presence of benzalkonium chloride, planktonic growth was significantly inhibited by a fourfold lower antiseptic concentration than biofilm development. For Staphylococcus epidermidis CIP53124 in the presence of antiseptics at the minimal inhibitory concentration (MIC), a total inhibition of biofilm formation was observed. For Staph. epidermidis exposed to chlorhexidine at 1/2, 1/4 and 1/8 MIC, or to benzalkonium chloride at 1/8, 1/16 or 1/32 MIC, biofilm formation was increased from 11.4% to 22.5% without any significant effect onto planktonic growth. Chlorhexidine and benzalkonium chloride inhibited biofilm formation of different bacterial species but were able to induce biofilm development for the Staph. epidermidis CIP53124 strain at sub-MICs. Sublethal exposure to cationic antiseptics may contribute to the persistence of staphylococci through biofilm induction.