Inhibition of Aspergillus fumigatus and Its Biofilm by Pseudomonas aeruginosa Is Dependent on the Source, Phenotype and Growth Conditions of the Bacterium

Abstract

Aspergillus fumigatus (Af) and Pseudomonas aeruginosa (Pa) are leading fungal and bacterial pathogens, respectively, in many clinical situations. Relevant to this, their interface and co-existence has been studied. In some experiments in vitro, Pa products have been defined that are inhibitory to Af. In some clinical situations, both can be biofilm producers, and biofilm could alter their physiology and affect their interaction. That may be most relevant to airways in cystic fibrosis (CF), where both are often prominent residents.We have studied clinical Pa isolates from several sources for their effects on Af, including testing involving their biofilms. We show that the described inhibition of Af is related to the source and phenotype of the Pa isolate. Pa cells inhibited the growth and formation of Af biofilm from conidia, with CF isolates more inhibitory than non-CF isolates, and non-mucoid CF isolates most inhibitory. Inhibition did not require live Pa contact, as culture filtrates were also inhibitory, and again non-mucoid>mucoid CF>non-CF. Preformed Af biofilm was more resistant to Pa, and inhibition that occurred could be reproduced with filtrates. Inhibition of Af biofilm appears also dependent on bacterial growth conditions; filtrates from Pa grown as biofilm were more inhibitory than from Pa grown planktonically. The differences in Pa shown from these different sources are consistent with the extensive evolutionary Pa changes that have been described in association with chronic residence in CF airways, and may reflect adaptive changes to life in a polymicrobial environment.

Effects of Iron Chelators on the Formation and Development of Aspergillus fumigatus Biofilm

“…This is similar to the polymorphism seen when surveying random clinical A. fumigatus isolates for susceptibility to antifungal drugs (2,17). The greater susceptibility of biofilm formation than that of preformed biofilm to a chelator is consistent with the differential effects of Pseudomonas aeruginosa cells (or culture filtrates) on A. fumigatus biofilm demonstrated in our previous studies (18).…”

“…We chose to first test the effects of DFP and DFM on the development of A. fumigatus biofilms. Our laboratory first utilized and reported on a 12-well assay for studies of A. fumigatus biofilm development (18). In later studies, an assay using 96-well plates was explored.…”

Interdependence between iron acquisition and biofilm formation in Pseudomonas aeruginosa

“…This iron-chelating activity gives P. aeruginosa an advantage during polymicrobial interactions. For instance, P. aeruginosa inhibits Aspergillus fumigatus biofilm formation via Pf4-mediated iron sequestration (Ferreira et al ., 2015; Penner et al ., 2016). Pf4 bacteriophage can inhibit A. fumigatus biofilms even in the absence of live P. aeruginosa , but this inhibition is deterred by supplementation of ferric iron (Penner et al ., 2016).…”

Harnessing Bacterial Signals for Suppression of Biofilm Formation in the Nosocomial Fungal Pathogen Aspergillus fumigatus

“…In the case of CF, A. fumigatus has been isolated in up to 60% of patients with Pseudomonas aeruginosa infection, suggesting a close relationship between established colonization by P. aeruginosa and superinfection by A. fumigatus (Paugam et al, 2010; Briard et al, 2015). Interkingdom interactions between A. fumigatus and bacterial competitors has been described previously, with significant attention focused on the interaction with P. aeruginosa (McAlester et al, 2008; Mowat et al, 2010; Briard et al, 2015; Ferreira et al, 2015; Zheng et al, 2015). Perhaps somewhat surprisingly, given their co-occurrence, many of these studies describe an antagonistic influence of P. aeruginosa secreted factors on A. fumigatus biofilm formation.…”