Evasion of neutrophil-mediated bacterial clearance in Pseudomonas aeruginosa isolates from new-onset infections in cystic fibrosis children

Abstract

Chronic Pseudomonas aeruginosa (PA) infections in cystic fibrosis (CF) patients can persist for decades and are associated with poor clinical outcomes. New-onset PA infections are routinely treated with antibiotics, but unfortunately up to 40% of patients fail eradication therapy due to reasons that are poorly understood. Recently, we found that Persistent PA isolates from CF patients who failed tobramycin eradication therapy were more resistant to in vitro neutrophil-mediated opsonophagocytosis and intracellular bacterial killing (OPK) and were significantly associated with a non-twitching phenotype compared to Eradicated isolates. In this study, we sought to investigate how Persistent isolates evade in neutrophil-mediated bacterial clearance in vitro and whether these PA isolates also persist in vivo. Furthermore, we investigated whether restoring pilus-mediated twitching motility is sufficient to restore susceptibility to in vitro OPK and in vivo bacterial clearance. Using primary murine serum and bone marrow-derived neutrophils, we demonstrated that Persistent isolates are resistant to several neutrophil antibacterial functions compared to Eradicated isolates. Additionally, mice failed to clear pulmonary infections caused by Persistent isolates but not Eradicated isolates despite comparable responses in leukocyte recruitment and cytokine responses. We demonstrate that loss of Type IV pilus-mediated twitching motility confers a fitness advantage for a Persistent isolate during a murine pulmonary infection, and restoration of pilus-mediated twitching motility improves in vivo bacterial clearance. Our findings show that resistance to neutrophil-mediated bacterial clearance in Persistent isolates are partly mediated by loss of Type IV pilus-dependent motility and contributes to the persistence of new onset PA infections.