Multilevel antimicrobial polymer system against surrogate viruses : effect on their viability and potential mode of action

Abstract

The COVID-19 pandemic has underscored the significance of ensuring the health and safety of individuals, particularly in indoor settings where people spend most of their time, especially in places such as Hong Kong. Hence, there is a rising interest in developing antimicrobials capable of inactivating various viruses, including emerging pathogens. This study delves into the virucidal effect of a multilevel antimicrobial polymer (MAP) system on surrogate viruses. The study focuses on investigating the susceptibility of bacteriophages, the potential mechanisms of action, and the variables influencing the long-term efficacy of the MAP system in actual environmental conditions. The first part of the study is the preparation and characterization of the MAP system, which includes polyvinyl alcohol (PVA), polyhexamethylene biguanide (PHMB), and polyethyleneimine (PEI). PHMB and PEI have demonstrated antimicrobial properties against both bacteria and viruses. These polymers will be blended with PVA to improve their film-forming ability and physical properties. The second part of this study focuses on examining the effect of the multilevel antimicrobial polymer (MAP) system on the viability of four surrogate viruses. This chapter will use bacteriophages as surrogate viruses. These bacteriophages and their representative characteristics are as follows: 1.Phi 6: This surrogate virus represents small, enveloped viruses. 2.MS2: This surrogate virus represents small, non-enveloped RNA viruses. 3.PhiX174: This surrogate virus represents small, non-enveloped DNA viruses. 4.T7: This surrogate virus represents medium-tailed DNA viruses. Chapter 2 revealed varying susceptibility of the four bacteriophages to MAP, with Phi 6 being the most susceptible, followed by T7, MS2, and PhiX174. The kinetic curves differed from the linear Chick-Watson equation, which describes the disinfectant's dose and time dependence. The Chick-Watson-Hom equation showed that the curves follow a tailing-off behavior. This suggests that additional factors beyond contact time and disinfection dose are at play, such as inhomogeneity within the viral suspension and depletion of the MAP solution over time. Lastly, the results show that the virucidal activity of MAP against the four bacteriophages is not dose-dependent. In the third part of this study, the focus is on examining the synergistic effect of the components of the multilevel antimicrobial polymer (MAP) system on its virucidal activity against three susceptible bacteriophages: Phi 6, MS2, and T7. The goal is to understand how the combination of polyvinyl alcohol (PVA), polyhexamethylene biguanide (PHMB), and polyethyleneimine (PEI) in the MAP system enhances its ability to inactivate these specific viruses. In addition to investigating the virucidal activity, this part also aims to assess the improvement in the coating properties of the MAP system. This includes examining the surface morphology, water contact angle, and thermal stability of the MAP solution as a coating material. Results showed that PHMB alone showed high virucidal activity for all viruses, and the addition of PEI enhanced this activity synergistically. PVA did not have virucidal activity on its own but enhanced the effect of the active components, except for T7, where it had an antagonistic effect. There are also changes in the physical properties, such as the surface morphology, improved hydrophobicity, and thermal stability. The final part of this study aims to investigate how the multilevel antimicrobial polymer (MAP) system affects the structural integrity of susceptible bacteriophages. Additionally, this part of the study aims to identify environmental factors that can either accelerate or protect the bacteriophages after treatment with the MAP system. TEM analysis showed distinct cleavage points in MS2 bacteriophages, suggesting that MAP targets the A-protein involved in viral attachment and genome delivery. Phi 6 bacteriophages exhibited more extensive damage to capsids, particularly in individual virions and those on the periphery of aggregates. Treated T7 samples displayed irregular capsids, collapsed heads, detached tails, and tail fibers. By exploring these factors, the study aims to provide a comprehensive understanding of the long-term effectiveness of the MAP system in real-world environmental conditions. This information will contribute to our overall understanding of the MAP system's performance and potential applications.

Date of Award	2024
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology
Supervisor	King Lun YEUNG (Supervisor) & Wei HAN (Supervisor)