AUTHOR=Kaur Jashanpreet , Pethani Bhavin P. , Kumar Sheemal , Kim Minkyoung , Sunna Anwar , Kautto Liisa , Penesyan Anahit , Paulsen Ian T. , Nevalainen Helena 

TITLE=Pseudomonas aeruginosa inhibits the growth of Scedosporium aurantiacum, an opportunistic fungal pathogen isolated from the lungs of cystic fibrosis patients

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.00866

DOI=10.3389/fmicb.2015.00866

ISSN=1664-302X

ABSTRACT=<p>The filamentous fungus <italic>Scedosporium aurantiacum</italic> and the bacterium <italic>Pseudomonas aeruginosa</italic> are opportunistic pathogens isolated from lungs of the cystic fibrosis (CF) patients. <italic>P. aeruginosa</italic> has been known to suppress the growth of a number of CF related fungi such as <italic>Aspergillus fumigatus, Candida albicans</italic>, and <italic>Cryptococcus neoformans</italic>. However, the interactions between <italic>P. aeruginosa</italic> and <italic>S. aurantiacum</italic> have not been investigated in depth. Hence we assessed the effect of <italic>P. aeruginosa</italic> reference strain PAO1 and two clinical isolates PASS1 and PASS2 on the growth of two clinical <italic>S. aurantiacum</italic> isolates WM 06.482 and WM 08.202 using solid plate assays and liquid cultures, in a synthetic medium mimicking the nutrient condition in the CF sputum. Solid plate assays showed a clear inhibition of growth of both <italic>S. aurantiacum</italic> strains when cultured with <italic>P. aeruginosa</italic> strains PASS1 and PAO1. The inhibitory effect was confirmed by confocal microscopy. In addition to using chemical fluorescent stains, strains tagged with yfp (<italic>P. aeruginosa</italic> PASS1) and mCherry (<italic>S. aurantiacum</italic> WM 06.482) were created to facilitate detailed microscopic observations on strain interaction. To our knowledge, this is the first study describing successful genetic transformation of <italic>S. aurantiacum</italic>. Inhibition of growth was observed only in co-cultures of <italic>P. aeruginosa</italic> and <italic>S. aurantiacum</italic>; the cell fractions obtained from independent bacterial monocultures failed to initiate a response against the fungus. In the liquid co-cultures, biofilm forming <italic>P. aeruginosa</italic> strains PASS1 and PAO1 displayed higher inhibition of fungal growth when compared to PASS2. No change was observed in the inhibition pattern when direct cell contact between the bacterial and fungal strains was prevented using a separation membrane suggesting the involvement of extracellular metabolites in the fungal inhibition. However, one of the most commonly described bacterial virulence factors, pyocyanin, had no effect against either of the <italic>S. aurantiacum</italic> strains. This study shows that <italic>P. aeruginosa</italic> has a substantial inhibitory effect on the growth of the recently described CF fungal pathogen <italic>S. aurantiacum</italic>. The findings also highlighted that <italic>P. aeruginosa</italic> biofilm formation is important but not crucial for inhibiting the growth of <italic>S. aurantiacum</italic> in a lung- mimicking environment.</p>