Enterococcus spp. dry surface biofilm resilience to disinfection

Dry surface biofilms (DSB) are increasingly recognised as reservoirs of healthcare-associated pathogens that contribute to environmental persistence and transmission. However, the susceptibility of enterococcal DSB to disinfectants remains poorly understood.

To evaluate the efficacy of commonly used disinfectants against enterococcal DSB and identify best practices for their removal.

The efficacy of benzalkonium chloride (BZC), sodium dichloroisocyanurate (NaDCC), sodium hypochlorite (NaOCl), a complex cationic formulation, and two peracetic acid (PAA)-based formulations was assessed against hydrated and dry surface biofilms of clinical and reference strains of enterococci in standard efficacy test procedures. The effects of disinfectant concentration, contact time, mechanical wiping, biofilm format, and surface material were also investigated.

Most BZC and NaDCC treatments failed to achieve the ≥4 Log₁₀ CFU/mL reduction, whereas selected PAA formulations consistently met this threshold. Increasing PAA concentration and contact time significantly improved efficacy. Mechanical wiping enhanced NaOCl performance, increasing bacterial reduction by a mean of 1.61 Log₁₀ CFU/mL, while a commercially available disinfectant wipe achieved a mean reduction of 5.31 Log₁₀ CFU/mL. Susceptibility varied with disinfectant chemistry and with the type of surface materials. Hydrated biofilms were less susceptible than DSB following BZC treatment, whereas no significant differences were observed with most PAA treatments. Likewise, BZC and NaDCC efficacy was generally lower against DSB on stainless steel compared to polycotton or polyester, but not following PAA treatment.

Enterococcal DSB exhibit substantial tolerance to several commonly used disinfectants, while selected PAA formulations consistently achieved accepted efficacy thresholds. Mechanical wiping significantly improved disinfectant performance, supporting the combined use of oxidising disinfectants and physical biofilm disruption for effective surface decontamination.