In vitro effects of combined iron chelation, antibiotics and matrix disruption on clinical isolates of Pseudomonas aeruginosa

Objectives: Pseudomonas aeruginosa is an important pathogen in chronic suppurative respiratory diseases, with adverse effects on severity, healthcare utilization and quality of life. Aerosolized combined biofilm disruption and iron chelators offer novel proof-of-concept for improving airway antimicrobial efficacy. Our aim was to assess the activity of desferrioxamine, Dornase alfa (DNase) and antibiotics on biofilm formation and against mature preformed biofilms of P. aeruginosa. Methods: Fifty-six isolates of P. aeruginosa were screened for biofilm production and seven isolates with varying capacity to form biofilms were referred for further study. Three antibiotics (colistin, tobramycin and ciprofloxacin) as well as desferrioxamine and DNase were assessed for their ability to prevent biofilm formation using the crystal violet assay. The same method was used to assess their impact on mature biofilms. Each agent, as well as combinations of these agents, was also assessed for its effect on the metabolic activity and viability of preformed P. aeruginosa biofilm by the resazurin reduction assay and by performing viable counts. Results: Antibiotics alone prevented the development of biofilms and partly reduced the viability of mature biofilms. Desferrioxamine and DNase did not reduce biofilm formation. For most isolates, desferrioxamine and DNase did not offer any clear advantage over the use of antibiotics alone with respect to reducing the viability of Pseudomonas biofilms. Conclusions: Colistin, tobramycin and ciprofloxacin prevented biofilm formation by P. aeruginosa and reduced the viability of mature biofilms. For most isolates, there was no clear advantage of combining these antimicrobials with desferrioxamine or DNase.