Small Colony Variants of Pseudomonas aeruginosa Display Heterogeneity in Inhibiting Aspergillus fumigatus Biofilm

Abstract

Pseudomonas aeruginosa and Aspergillus fumigatus are major microbes in cystic fibrosis (CF). We reported non-mucoid P. aeruginosa isolates more inhibitory to A. fumigatus than mucoid ones. Another CF P. aeruginosa phenotype, small colony variants (SCVs), is an unknown factor in intermicrobial competition with A. fumigatus. Clinical SCV isolates and reference CF non-mucoid isolate (Pa10, producing normal-sized colonies) were compared. Live cells of P. aeruginosa or filtrates from P. aeruginosa planktonic or biofilm cultures were co-incubated with A. fumigatus growing under conditions allowing biofilm formation or with preformed biofilm. Metabolic activity of A. fumigatus biofilm was then measured. When necessary, assays were done after adjustment for growth differences by adding fresh medium to the planktonic culture filtrate. Pyoverdine determinations were performed spectrophotometrically on the planktonic culture filtrates. In all experimental conditions (live cells and planktonic or biofilm culture filtrates of P. aeruginosa versus A. fumigatus biofilm formation or preformed biofilm), three SCV isolates were less inhibitory than Pa10, two equal or more inhibitory. Adjusting planktonic culture filtrates for growth differences showed SCV inhibition differences variably related to growth or deficient inhibitor production. Studies suggested the principal P. aeruginosa inhibitor to be pyoverdine. SCV isolates appear heterogeneous in their capacity to inhibit A. fumigatus biofilm. SCV isolates can be important in the CF microbiome, because they are capable of intermicrobial inhibition.

The myriad challenges of respiratory fungal infection in cystic fibrosis

“…In vitro work suggests competitive inhibition of A fumigatus biofilm formation by small molecules produced by P aeruginosa . However, the degree of inhibition seen in vitro appears to be dependent on the source, phenotype, and growth conditions of the P aeruginosa . P aeruginosa interactions with fungi are not limited to Aspergillus , with studies also showing inhibition of Scedosporium and Lomentospora spp., and inhibition of biofilm development with Candida spp .…”

Fungal Respiratory Infections in Cystic Fibrosis (CF): Recent Progress and Future Research Agenda

“…SCV P. aeruginosa isolates displayed heterogeneity in their inhibition of A. fumigatus biofilm vis-à-vis the nonmucoid bacterial strains. Further, P. aeruginosa pyoverdine production correlated with A. fumigatus inhibition [25]. Thus, the two complementary experimental studies have advanced our understanding of bacterial-fungal pathogens interactions likely to take place in CF patients.…”

“…Host response of fungal diseases in CF patients [21] 7. Fungal virulence mechanisms [22][23][24][25][26][27] large study involved 243 CF patients from seven centers in France over a 15-month period. The investigators found that about half of the patients presented with at least one fungal species, while 37% were co-colonized with two species.…”

“…Two research groups report inhibitory activities of P. aeruginosa on Scedosporium species, L. prolificans and A. fumigatus [24,25]. Chen et al [24] discovered that nonmucoid P. aeruginosa strain caused more inhibition of S. aurantiacum and L. prolificans in vitro.…”

“…These exciting findings would allow future examination of the mechanism of colonization and infection caused by Scedosporium and Lomentospora in CF lungs where P. aeruginosa mucoid forms are predominant. Anand et al [25] build upon the previous findings on the inhibition of A. fumigatus biofilms by non-mucoid P. aeruginosa by focusing on the role of small colony variants (SCV) of the bacterial pathogen on fungal inhibition. SCV P. aeruginosa isolates displayed heterogeneity in their inhibition of A. fumigatus biofilm vis-à-vis the nonmucoid bacterial strains.…”