Phenotypical Characteristics of the Black Yeast Exophiala dermatitidis Are Affected by Pseudomonas aeruginosa in an Artificial Sputum Medium Mimicking Cystic Fibrosis–Like Conditions

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 CFassociated 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, lasR, and rhlR 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.

Stenotrophomonas maltophilia affects the gene expression profiles of the major pathogens Pseudomonas aeruginosa and Staphylococcus aureus in an in vitro multispecies biofilm model

“…The filamentation of C. albicans was also strongly reduced in the presence of P. aeruginosa over time. Similar effects have been reported for co-culture experiments of P. aeruginosa and the black yeast Exophiala dermatitidis in cystic fibrosis (CF)-like environment, and it was shown that the quorum-sensing molecules N-acyl homoserine lactone (AHLs) of P. aeruginosa play a major role in this phenotype ( 55 ).…”

Innovative Strategies to Overcome Antimicrobial Resistance and Tolerance

“…Therefore, use of host-like conditions in microbial susceptibility testing, including biofilm-related tolerance, supports in identifying specific drug targets, as well as unraveling the bacterial physiology, along with physiological and metabolic basis of biofilm formation [ 61 , 68 ]. By using this approach, growth, biofilm formation, and antimicrobial tolerance have not only been assessed for P. aeruginosa , but also for other microorganisms colonizing the cystic fibrosis lung, including Stenotrophomonas maltophilia , Mycobacterium abscessus, and black yeast [ 69 , 70 , 71 ]. It is worth mentioning that the antimetabolite oxythiamine was initially identified as an antimicrobial agent in artificial sputum medium, showing synergistic effects in combination with tetracycline for which P. aeruginosa is intrinsically resistant [ 72 ].…”

Nitrogen isotope effects can be used to diagnose N transformations in wastewater anammox systems

“…Ammonium is completely consumed in many ecosystems, but where isotope effects are permitted to be expressed ( e.g. , anoxic sediments and waters/ocean basins), its δ 15 N is thought to reflect the balance between N fixation, with a 15 ε near 0‰; aerobic ammonia oxidation, with a variable isotope effect between 14‰ and 46‰ 14 – 17 ; and assimilation (4‰ to 27‰) 18 . For anammox, a very limited number of isotope studies have constrained 15 N/ 14 N isotope effects in enriched cultures 10 , 19 , while one study has estimated their values in wastewater incubations 20 .…”