The criteria for chronic rhinosinusitis in children with cystic fibrosis are rarely fulfilled after initiation of CFTR modulator treatment.

The vast majority of people with cystic fibrosis (pwCF) have untreated secondary chronic rhinosinusitis (CRS). Whereas the introduction of the cystic fibrosis transmembrane conductance regulator modulator (CFTRm) treatment regime has improved the lung function of pwCF, few studies have been published examining the effect on sinonasal symptoms in children. Our aim was to explore the effect of double CFTRm treatment on CRS and olfaction in children with CF. pwCF were included in this non-randomized cross-sectional study, where an otolaryngologist performed a complete ENT examination before initiating treatment with elaxacaftor/tezacaftor/ivacaftor (ETI). Twenty-three pwCF aged 6-12 years were included. Eighteen of 23 patients were on a double CFTRm treatment, and 5 patients were CFTRm naive, respectively. Altogether, 19 had normal olfaction, 20 had none or mild CRS symptoms according to SNOT-22, and 14 had a normal endoscopy. None of the patients had symptoms of chronic rhinosinusitis lasting for more than 12 weeks, thus none of the patients fulfilled the criteria for CRS. Children with CF treated with double CFTRm have few to no symptoms of CRS and normal olfaction, which is an improvement compared with children following treatment modalities prior to CFTRm.

Mutations in the efflux pump regulator MexZ shift tissue colonization by Pseudomonas aeruginosa to a state of antibiotic tolerance.

Mutations in mexZ, encoding a negative regulator of the expression of the mexXY efflux pump genes, are frequently acquired by Pseudomonas aeruginosa at early stages of lung infection. Although traditionally related to resistance to the first-line drug tobramycin, mexZ mutations are associated with low-level aminoglycoside resistance when determined in the laboratory, suggesting that their selection during infection may not be necessarily, or only, related to tobramycin therapy. Here, we show that mexZ-mutated bacteria tend to accumulate inside the epithelial barrier of a human airway infection model, thus colonising the epithelium while being protected against diverse antibiotics. This phenotype is mediated by overexpression of lecA, a quorum sensing-controlled gene, encoding a lectin involved in P. aeruginosa tissue invasiveness. We find that lecA overexpression is caused by a disrupted equilibrium between the overproduced MexXY and another efflux pump, MexAB, which extrudes quorum sensing signals. Our results indicate that mexZ mutations affect the expression of quorum sensing-regulated pathways, thus promoting tissue invasiveness and protecting bacteria from the action of antibiotics within patients, something unnoticeable using standard laboratory tests.