Macquarie University
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Biofilms in healthcare: difficulty in removal

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posted on 2023-07-24, 04:06 authored by MST Farhana Parvin

Hospital surfaces and medical devices play important role in infection transmission. Bacteria typically attach to surfaces and exude a slimy matrix mostly consisting of protein, carbohydrate, and DNA that surrounds and shields them from the external environment, eventually forming a mature biofilm. Furthermore, recent discoveries of biofilms on dry hospital surfaces and the continuing problem of biofilms protecting pathogens in endoscopes highlight the limitations of existing cleaning and disinfection procedures. Biofilms on surfaces act as a reservoir for pathogens and thus increases the likelihood of HAI (Healthcare associated infection) transmission and development. Therefore, cleaning, and disinfecting surfaces of healthcare settings is critical for avoiding HAI and ensuring patient safety.

Aims of this study: 1) To compare surface roughness and bacterial attachment in used and new endoscope channels in vivo and in vitro. 2) To determine dry surface biofilm (DSB) removal using standard wiping process. 3) To compare the effectiveness of different commercial surgical washes containing commonly used topical antimicrobial agents against various bacterial species using biofilm models that use different culture conditions. 4) To determine the efficacy of combined chemical (antimicrobial instillation) and physical (negative pressure wound therapy- NPWT) against multispecies bacterial biofilm. 5) To investigate the phenotypic and ultrastructural changes of Staphylococcus aureus grown under different culture conditions.

This study revealed that: 1) Increased surface roughness is involved with bacterial attachment and biofilm formation in endoscope channels. 2) Staphylococcus aureus dry DSB is significantly more difficult to remove than dried planktonic bacteria. In addition, DSB is hard to completely remove even wiping in moistened condition. 3) Efficacy of surgical washes vary depending on the bacterial growth mode, bacterial species, and wash additives. 4) Combined physical (NPWT) and chemical (instillation antimicrobials) treatment was more effective than physical treatment alone against multispecies bacterial biofilm. 5) Growth conditions and age of culture has a major impact on cell wall synthesis. Decreased water availability resulted in the thickest cell wall and greatest amount of EPS (Extracellular polymeric substances).

Overall, this study demonstrated that conventional infection control measures are insufficient to remove/kill mature biofilm and therefore additional research into optimising cleaning and disinfection needs to be conducted with the of decreasing HAI and ensuring patient safety. Furthermore, ultrastructural studies revealed that the thickened cell wall of DSB might contribute to DSB antimicrobial resistance and could be a target for new effective disinfectants.


Table of Contents

Chapter One: Literature Review -- Chapter two: Impact of surface roughness in bacterial attachment -- Chapter three: Difficulties in dry surface biofilm removal using standard wiping process -- Chapter four: Antimicrobial’s efficacy testing against monospecies and multispecies biofilms -- Chapter five: Potential mechanisms of Staphylococcus aureus biofilm resistance -- Chapter six: General discussion -- References -- Appendices


Thesis by publication

Awarding Institution

Macquarie University

Degree Type

Thesis PhD

Department, Centre or School

Department of Biomedical Sciences

Year of Award


Principal Supervisor

Karen Vickery

Additional Supervisor 1

Honghua Hu

Additional Supervisor 2

Helen Rizos


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