Comparison of three methods for claiming biofilm disinfection

Biofilms are frequently associated with hospital-acquired infections. To reduce patient risks, disinfectant should be able to inactivate bacteria present within biofilms. Multiple methods are described in the literature, but no consensus has been reached for disinfection efficacy tests against biofilms.

Three published Pseudomonas aeruginosa biofilm growing methods were characterized by measuring protein, total organic carbon (TOC), and bacterial concentrations. The sensitivity of each biofilm to disinfectant was then evaluated according to a test method based on NF EN 14561 against a reference peracetic acid (PAA) solution.

Biofilms formed according to ISO 15883-5 showed higher protein and bacteria contents than biofilms formed using ASTM E2562 or the Konrat et al. method. The results indicate that ISO 15883-5 biofilms were less sensitive to disinfectant than the two other biofilms, and that older biofilms had lower sensitivity to disinfectant.

This study found direct correlation between the duration of growth and the maturity of biofilms. ISO 15883-5 biofilms grown for 96 h were found to have higher concentrations of protein, TOC and bacteria than ASTM E2652 and Konrat et al. biofilms grown for 48 h and 24 h, respectively. The importance of the biofilm maturation phase was confirmed by the disinfection efficacy tests. The results of these tests demonstrate that biofilms with the longest maturation phase are less sensitive to disinfectant. Type tests performed on disinfectants to demonstrate that they can be used on medical devices or in healthcare facilities should include tests against mature biofilms.