Involvement of small molecules in the interaction between Pseudomonas aeruginosa and Scedosporium aurantiacum

Pathogenic bacteria and filamentous fungi frequently coexist in airways of individuals with cystic fibrosis (CF) and increase morbidity and mortality rates. In this thesis, interactions were studied between the opportunistic bacterium Pseudomonas aeruginosa, and emerging fungal pathogen Scedosporium aurantiacum, which are prominent causes of CF infection in Australia. Co-cultivation of P. aeruginosa and S. aurantiacum on lung mimicking agarmedium revealed inhibitory effects of P. aeruginosa on fungal growth. The nature of interaction was explored using heat killed cells, cell lysate and culture supernatant of P. aeruginosa, indicating the necessity of live P. aeruginosa cells and/or intra and extracellular small molecules to inhibit the growth of S. aurantiacum. To identify molecular basis of interaction, small molecules were extracted using various solvents from cell lysates and culture supernatants of selected strains of P. aeruginosa and S. aurantiacum. The inhibitory activity of solvent fractions of P. aeruginosa against S. aurantiacum indicated presence of small bioactive molecules produced by the bacterium. The solvent fractions were partially characterised and fractionated using ultraviolet-visible spectroscopy and high performance liquid chromatography. The work contributes to characterisation of microbial interactions that may affect the lungs of people with CF, and the search for effective management of the disease.