Hydrogen peroxide and sodium hypochlorite disinfectants are more effective against Staphylococcus aureus and Pseudomonas aeruginosa biofilms than quaternary ammonium compounds.

Background: Antimicrobial disinfectants are used as primary treatment options against pathogens on surfaces in healthcare facilities to help prevent healthcare associated infections (HAIs). On many surfaces, pathogenic microorganisms exist as biofilms and form an extracellular matrix that protects them from the antimicrobial effects of disinfectants. Disinfectants are used as all-purpose antimicrobials though very few specifically make biofilm efficacy claims. The objective of this study was to evaluate the efficacy of eight registered disinfectants (six registered by the Environmental Protection Agency and two products registered in by the European Chemical Agency) with general bactericidal claims, but currently no biofilm efficacy claims, against Staphylococcus aureus ATTC-6538 and Pseudomonas aeruginosa ATCC-15442 biofilms. We hypothesized that hydrogen peroxide and sodium hypochlorite disinfectant products would be more effective than quaternary ammonium chlorides. Methods: This study tested the bactericidal efficacy of eight registered disinfectant products against S. aureus ATCC-6538 and P. aeruginosa ATCC-15442 grown on glass coupons using a Center for Disease Control (CDC) biofilm reactor and EPA MLB SOP MB-19. Bactericidal efficacy was determined after treating coupons with disinfectants following standard EPA MLB SOP MB-20. Results: Overall, sodium hypochlorite and hydrogen peroxide disinfectants had significantly higher bactericidal efficacies than quaternary ammonium chloride disinfectants. We also found that all tested disinfectants except for quaternary ammonium chloride disinfectants met and exceeded the EPA standard for bactericidal efficacy against biofilms. Conclusion: In general, bactericidal efficacy against biofilms differed by active ingredient. The efficacies of sodium hypochlorite and hydrogen peroxide disinfectants did not vary between strains, but there were significant differences between strains treated with quaternary ammonium chloride disinfectants.

Strain, disinfectant, concentration, and contact time quantitatively impact disinfectant efficacy.

Background: Transmission of healthcare-associated infections caused by antibiotic- and multi-drug resistant (MDR) pathogens (e.g. Methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa) are a major concern in patient care facilities. Disinfectant usage is critical to control and prevent pathogen transmission, yet the relationships among strain, disinfectant type, contact time, and concentration are not well-characterized. We hypothesized that there would be significant differences in disinfectant efficacy among clinically relevant strains under off-label disinfectant conditions, but there would be less no differences among at registered label use concentrations and contact times. The purpose of this study was to quantify the effect of disinfectant concentration and contact time on the bactericidal efficacy of clinically relevant strains of S. aureus and P. aeruginosa. Methods: Accelerated hydrogen peroxide (AHP), quaternary ammonium compounds (Quat), and sodium hypochlorite were tested at label and reduced contact times and concentrations against four MDR P. aeruginosa strains and four MRSA strains. Quantitative EPA method MB-25-02 was used to measure disinfectant efficacy reported as log10 reduction. Results: Both off-label disinfectant concentrations and contact times significantly affected efficacy of all disinfectants tested. Bactericidal efficacy varied among MRSA and P. aeruginosa strains. Conclusions: The quantitative disinfectant efficacy method used highlights the inter-strain variability that exists within a bacterial species. It also underscores the need for a disinfectant validation method that takes these variances into account.