Mechanisms of action of polyhexamethylene biguanide-based biocides against non-enveloped virus

Human viral pathogens place a serious threat on the healthcare system. Adequate and efficient disinfection procedures minimise the incidence of surface contamination and viral disease transmission. Biocide type, environmental conditions and viral characteristics e.g. presence of envelope influence the disinfection effectiveness. Thus, understanding the mechanisms of virucidal action is essential for improving disinfection efficacy. PHMB has a wide range of antimicrobial activities, but its action against viruses has been mostly tested on enveloped viruses, which appeared to be inactivated. This project aimed at understanding the mechanisms of action of two PHMB-based biocides, VANTOCIL TG and COSMOCILIMCQ, against non-enveloped viruses including the bacteriophages MS2 and F116 used as model viruses, and the human Adenovirus type5. Biocides were tested in a suspension test at different conditions. Hydrophobicity tests, SDS-PAGE, DNA analysis, dynamic light scattering and transmission electron microscopy were performed. Suspension tests at 20 °C showed that PHMBs at 800 ppm reduced MS2 and Ad5 by 90. Higher reduction was achieved against Fl 16 99. Times of exposure did not increase the activity, whereas temperature had a great effect. At 30 °C 99.99 of MS2 was inactivated after 10 min the efficacy against Ad5 was also enhanced, but to minor extent. Despite a modest activity, PHMB interacted with the viral capsid producing damage which was very specific against Ad5. Viral aggregation played a key role in limiting virucidal efficacy of PHMB, especially concerning MS2. It is likely that the observed capsid damage caused the inactivation. However, the hypothesis of domain formation by PHMB and thus the inhibition of the virus-host interaction cannot be ruled out. The mechanism of binding PHMB molecules to the viruses was highly cooperative and occurred through first electrostatic and then hydrophobic forces. Concluding, it is the first time that PHMB-based biocides were shown to interact with viral capsid resulting in virucidal activity against non-enveloped viruses. However, such activity is reduced by formation of viral aggregates. Results supported also the use of MS2 as a surrogate of human RNA non-enveloped viruses