• cystic fibrosis

In 1999, Ramsey and colleagues published the results of a clinical trial of aerosolised tobramycin in cystic fibrosis (CF) to target chronic Pseudomonas aeruginosa infection.1 In keeping with their earlier demonstration of efficacy,2 they reported treatment to be associated with a reduction in P. aeruginosa sputum density and substantial clinical benefit (improved lung function and reduced risk of hospitalisation). Consistent findings were reported in subsequent studies,3 4 leading tobramycin inhaled powder/solution (TIP/S) maintenance therapy to go on to become the most common antibiotic used to treat people with cystic fibrosis (PWCF). While none of these studies related clinical outcome to microbiological impact directly, it is widely assumed that depletion of P. aeruginosa underpins TIP/S benefit.

This presumptive mechanism of TIP/S, and its limitation to those with chronic P. aeruginosa infection, has been challenged by two recent studies. In this issue, Heirali and colleagues report an investigation of the microbial predictors of response to TIP/S in adults with CF.5 16S rRNA gene amplicon sequencing was applied to banked sputum samples from 41 patients with chronic P. aeruginosa infection who had received TIP/S for at least 1 year and from whom sputum samples were available before and after the initiation of therapy. Somewhat unexpectedly, their study determined response to therapy (defined by the absence of a net decrease in forced expiratory volume in one second (FEV₁)) to be associated with higher relative abundance of staphylococci …