Pseudomonas aeruginosa (Pa) and Aspergillus fumigatus (Af) are the leading bacterial and fungal pathogens in cystic fibrosis. We have previously shown that Af biofilm formation or preformed biofilm is susceptible to inhibition by Pa cells, planktonic growth culture filtrate or biofilm growth culture filtrate, with a hierarchy of cystic fibrosis (CF) nonmucoid Pa, CF mucoid Pa, non-CF Pa most inhibitory to least inhibitory.a These studies were performed largely with a reference virulent non-CF Af, 10AF, though comparison with a few non-CF Af showed no difference in susceptibility compared to 10AF. Given differences in CF Pa from other Pa, this study addressed whether CF Af, whether as a result of residence in the unusual (consistency, ionic) and inflammatory CF airway milieu, with exposure to other airway microbes, or exposure to therapeutic antimicrobials, might show a different susceptibility to Pa.
A nonmucoid CF Pa, Pa10, known to inhibit 10AF, was studied. Live Pa cells or culture filtrates from planktonic Pa growth or growth as Pa biofilm were incubated with each of 12 sputum-derived CF Af or 12 non-CF Af, during Af biofilm formation or on preformed Af biofilm (thus 6 possible conditions compared/isolate). 10AF was included in every assay as a positive control. Comparisons were made with each Af in the absence of Pa or Pa product, and expressed as % of this control. A 96-well plate, RPMI1640 medium, and XTT readout of Af inhibition were used as previously describedb, with 8 replicate wells/experimental condition each time. P<0.05 was considered significant.
(Table; mean values of % of control shown). CF and non-CF Af isolates did not differ in any of the 6 sets of studies (P≥0.4); laboratory strain 10AF was slightly more inhibited than either wild-type in some assays (P>0.05).
CF and non-CF Af isolates form biofilm, and did not differ with respect to intermicrobial inhibition by an inhibitory CF Pa. A caveat is that it is unknown how long an Af isolated from a CF patient’s sputum has been in residence in the airway.