Purpose: Anti-virulence strategies have not been evaluated for the prevention of bacterial infections. Prolonged colonization of intubated patients with Pseudomonas aeruginosa isolates producing high-levels of the quorum sensing (QS)-regulated virulence factor rhamnolipids has been associated with ventilator-associated pneumonia (VAP). In this pathogen, azithromycin reduces QS-regulated virulence. We aimed to assess whether azithromycin could prevent VAP in patients colonized by rhamnolipids producing isolates.
Methods: In a randomized, double-blind, multicenter trial, intubated colonized patients received either 300 mg/day azithromycin or placebo. Primary endpoint was the occurrence of P. aeruginosa VAP. We further identified those patients persistently colonized by isolates producing high-levels of rhamnolipids and therefore at the highest risk to develop VAP linked to this QS-dependent virulence factor.
Results: Ninety-two patients were enrolled; 43 azithromycin-treated and 42 placebo patients were eligible for the per-protocol analysis. In the per-protocol population, the occurrence of P. aeruginosa VAP was reduced in the azithromycin group but without reaching statistical significance (4.7 vs. 14.3 % VAP, p = 0.156). QS-dependent virulence of colonizing isolates was similarly low in both study groups, and only five patients in each arm were persistently colonized by high-level rhamnolipids producing isolates. In this high-risk subgroup, the incidence of VAP was reduced fivefold in azithromycin versus placebo patients (1/5 vs. 5/5 VAP, p = 0.048).
Conclusions: There was a trend towards reduced incidence of VAP in colonized azithromycin-treated patients. In addition, azithromycin significantly prevented VAP in those patients at high risk of rhamnolipid-dependent VAP, suggesting that virulence inhibition is a promising anti-microbial strategy.