(479) Biofilm formation of Pseudomonas aeruginosa isolated after initiation of CFTR-modulator therapy

Background: People with cystic fibrosis (CF) experience chronic airway infections, often caused by Pseudomonas aeruginosa. Although treatment with CFTR modulators decreases airway inflammatory markers and mucus plugging, it does not result in sustained decreases or eradication of P. aeruginosa [1,2]. Possibly, bacteria are protected in scarred lung regions or subpopulations of bacteria may be well-suited to withstand the new lung environment. We hypothesized that after initiation of CFTR modulator therapy, P. aeruginosa may persist by forming biofilms. Biofilms are bacterial aggregates encased in a biopolymer-rich extracellular matrix, which protects the bacteria from host defenses, antibiotics, and shear force. Biofilm formation could allow P. aeruginosa to persist under the higher airway shear forces due to lower mucus viscosity and increased mucociliary clearance following initiation of CFTR modulator therapy [3]. Support for the role of biofilm formation by P. aeruginosa in CF airway infections includes that P. aeruginosa isolated from chronic CF airway infections often displays an increased ability to form biofilms in vitro, and bacterial aggregates encased in biofilm matrix are present in expectorated sputum [4,5].

Methods: We tested biofilm formation by a panel of 85 P. aeruginosa isolates that were collected before and after initiation of treatment with the CFTR modulator elexacaftor/tezacaftor/ivacaftor (Trikafta) in pediatric patients (CF Isolate Core).

Results: Isolates displayed a range of biofilm formation and biofilm matrix compositions. Interestingly, biofilm-forming ability and types of biofilm matrix were similar for isolates collected from the same subject, regardless of whether the isolates were collected before or after initiation of CFTR modulator therapy. Indeed, we observed greater variation between isolates from different subjects than between isolates collected before and after initiation of treatment.

Conclusions: Our results highlight the range biofilm formation of P. aeruginosa isolates and suggest that the ability to form biofilms in vitro is not required for persistence of P. aeruginosa following initiation of CFTR modulator treatment.

Acknowledgements: This work was supported by the Cystic Fibrosis Foundation [REICHH19F5]

References: [1] Hisert KB, Heltshe SL, Pope C, Jorth P, Wu X, Edwards RM, et al. Restoring cystic fibrosis transmembrane conductance regulator function reduces airway bacteria and inflammation in people with cystic fibrosis and chronic lung infections. Am J Respir Crit Care Med. 2017 Jun 15;195(12):1617–28.

[2] Mainz JG, Arnold C, Wittstock K, Hipler U-C, Lehmann T, Zagoya C, et al. Ivacaftor reduces inflammatory mediators in upper airway lining fluid from cystic fibrosis patients with a G551D mutation: Serial non-invasive home-based collection of upper airway lining fluid. Frontiers in Immunology. 2021;12.

[3] Gloag ES, German GK, Stoodley P, Wozniak DJ. Viscoelastic properties of Pseudomonas aeruginosa variant biofilms. Scientific Reports. 2018 Jun 26;8(1):9691.

[4] Armbruster CR, Marshall CW, Garber AI, Melvin JA, Zemke AC, Moore J, et al. Adaptation and genomic erosion in fragmented Pseudomonas aeruginosa populations in the sinuses of people with cystic fibrosis. Cell Reports. 2021 Oct 19;37(3).

[5] Jennings LK, Dreifus JE, Reichhardt C, Storek KM, Secor PR, Wozniak DJ, et al. Pseudomonas aeruginosa aggregates in cystic fibrosis sputum produce exopolysaccharides that likely impede current therapies. Cell Reports. 2021 Feb 23;34(8):108782.