Influence of low-dose nitric oxide on mono- and mixed-species biofilms formed by bacteria isolated from cystic fibrosis patients

Abstract

Cystic fibrosis (CF) is an autosomal recessive disorder. One of the characteristic hallmarks of the disease is infection of the lung. Over the life time of a CF patient, a number of pulmonary exacerbations occur which result in irreversible lung damage. Despite continuous treatment with antimicrobials, microorganisms continue to persist in the CF lung due to the formation of biofilms. The biofilm mode of growth can display up to a 1000x greater tolerance to antimicrobial treatments than their free living planktonic counterparts. Hence, anti-biofilm therapy strategies are required to break up these tolerant microbial communities.

Nitric oxide (NO) is one of the proposed anti-biofilm therapies, which has been shown to successfully initiate biofilm dispersal of one of the most widely recognized CF pathogens, P. aeruginosa. The work in this thesis was undertaken to investigate the use of NO as a potential biofilm dispersing agent for the monospecies biofilms formed by other commonly identified CF microorganisms. The second chapter outlines the isolation of these microorganisms from CF sputum samples and describes the culture profiling results for the CF patient cohort sampled. The third results chapter examines the effect of NO on the monospecies biofilms formed the CF microorganisms isolated in chapter 2. A biofilm dispersal effect was not observed across a range of NO concentrations; however intriguingly there was an effect on biofilm cell viability for NO concentrations ≥ 100 pM. Chapter 4 outlines a mixed species biofilm model composed of CF isolates for P. aeruginosa and S. aureus and a method to recover and analyse genomic DNA from biofilms. Biofilm dispersal for this mixed species biofilm was not observed however a reduction in the S. aureus population fraction was noted. The work in Chapter 5 was undertaken to adapt a new fluorescence in situ hybridisation method CLASI-FISH for the identification of microorganisms within CF sputum.

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ORCID for Jeremy Webb: orcid.org/0000-0003-2068-8589

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