Evaluation of the effectiveness of hydrogen-peroxide-based disinfectants on biofilms formed by Gram-negative pathogens

SummaryBackgroundHydrogen peroxide (H2O2)-based disinfectants are widely used in a number of different healthcare settings to control bacterial colonization and contamination, and reduce the risk of cross-infection. Efficacy tests of these formulations are performed on planktonic cultures, although it is well known that biofilms are the dominant form of bacterial contamination and more difficult to eradicate.AimTo determine if the biofilms of three different Gram-negative pathogens associated with multi-drug-resistant phenotypes can be eradicated effectively using different H2O2-based disinfectants.MethodsPlanktonic cultures and single-species 24-h biofilms of seven strains of Acinetobacter spp., seven strains of Klebsiella pneumoniae and seven strains of Pseudomonas aeruginosa, including clinical isolates, were exposed to working concentrations of H2O2 and H2O2-based formulations for 1 min to 24 h. Survival was monitored.FindingsThe levels of susceptibility of planktonic cultures to unformulated and formulated H2O2 were similar in all organisms and strains tested, with minimum inhibitory concentrations ranging from 0.5 to 20 mM H2O2. However, biofilms showed up to 266-fold less sensitivity to H2O2 and its formulations. The level of reduced susceptibility correlated with the strain's propensity to form biofilm, and differed between species. The two formulations with additional acidic active ingredients performed better at short exposure times, whereas ethanol-containing products required longer exposure times to be effective.ConclusionBiofilms of a significant number of clinical isolates of multi-drug-resistant nosocomial pathogens are not susceptible to working concentrations of several H2O2-based disinfectants. This may compromise the ability to control these pathogens with such products.