Abstract
Research into the cooperative pathogenicity of microbes in cystic fibrosis (CF) lungs is crucial for an understanding of the pathophysiology of infections and the development of novel treatment strategies. This study investigated the impact of the common CF-associated bacterial pathogen Pseudomonas aeruginosa on the black yeast Exophiala dermatitidis. It evaluated the planktonic growth, biofilm formation, morphology, and virulence of the fungus in the presence or absence of P. aeruginosa. It also determined the role of P. aeruginosa quorum-sensing (QS) molecules within these interactions, e.g., by using sterile culture filtrate and QS-deficient mutants. P. aeruginosa is known to inhibit the planktonic growth of E. dermatitidis. We found that fungal biofilm formation increased in the presence of P. aeruginosa after 24 h but is decreased significantly after 48 h. This effect was reversed when, instead of QS wild-type strains, ΔlasR, and ΔrhlR mutants were added to E. dermatitidis biofilm formation. The number and length of hyphae were substantially reduced when E. dermatitidis was co-cultivated with P. aeruginosa, but not when it was co-cultivated with the mutants. Experiments testing the virulence of E. dermatitidis in the greater wax moth Galleria mellonella showed a synergetic effect on larval killing when E. dermatitidis was injected together with P. aeruginosa culture filtrate. Survival rates were decreased when biofilm culture filtrate was added but not when planktonic culture filtrate was added. In summary, P. aeruginosa affects the growth, morphology, biofilm formation, and virulence of E. dermatitidis. N-acyl-L-homoserine lactone (AHL) QS molecules regulated factors that have been shown to contribute to the inhibition of the ability of E. dermatitidis to form filaments and biofilm.
Highlights
The respiratory tract of cystic fibrosis (CF) patients is commonly colonized by a wide spectrum of microbiota of both bacterial and fungal species
This study investigated the impact of the common CFassociated bacterial pathogen Pseudomonas aeruginosa on the black yeast Exophiala dermatitidis
Growth was determined by counting Colony-forming units (CFU) in liquid culture at 35◦C with slight agitation over a period of 24 h
Summary
The respiratory tract of cystic fibrosis (CF) patients is commonly colonized by a wide spectrum of microbiota of both bacterial and fungal species. Some of those organisms are harmful pathogens, such as Pseudomonas aeruginosa, Staphylococcus aureus, or Burkholderia cepacia complex, which are associated with a decline in lung function (Hudson et al, 1993; Courtney et al, 2007), the role of others, including many fungal species, has not yet been clearly distinguished (Hauser et al, 2011). Chronic Pa infections among CF patients are commonly caused by biofilm-growing mucoid strains (Bjarnsholt et al, 2009) and are associated with poorer clinical outcome and higher mortality (Blanchard and Waters, 2019). P. aeruginosa has been reported to gain in resistance mechanisms towards antimicrobial therapy, among them the formation of biofilms (Breidenstein et al, 2011)
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