S5 Moraxella catarrhalis attaches to the ciliary tip causing ciliary dyskinesia

Abstract

Moraxella catarrhalis is a gram-negative diplococcus bacterium primarily infecting the inner ear and respiratory tract. It is thought to be responsible for up to 20% of bacterial otitis media and 10% of infective exacerbations of COPD. Though previously described as part of the commensal nasal microbiome, it has gained traction recently as a pathogen and has been shown to attach to the cilia of the respiratory epithelium. We believe the interaction between M. catarrhalis and cilia might mimic some symptoms associated with Primary Ciliary Dyskinesia and assessed the impact of M. catarrhalis on PCD diagnosis. Firstly, we retrospectively analysed microbiology data collected from 526 nasal brushing samples from children referred for testing for Primary Ciliary Dyskinesia at the Royal Brompton Hospital between Jan 2015–2018. M. catarrhalis was isolated in 43/485 non-PCD (9%) samples and 1/41 (2%) PCD samples. No relationship was found between presence of M. catarrhalis and degree of ciliation or ciliary beat frequency. However, there was an increased incidence of ciliary dyskinesia due to ‘bulbous/swollen ciliary tips’ in individuals with M. catarrhalis growth when assessed by high-speed video microscopy. Following this, we hypothesised that M. catarrhalis attachment to cilia was responsible for the abnormalities observed at the ciliary tip. Three-dimensional high-resolution electron microscopy (electron tomography) revealed diplococci bacteria with surface proteins in direct contact with the membrane of the ciliary tips. To confirm the observed ciliary dyskinesia in the ex-vivo samples was due to M. catarrhalis attachment, air-liquid interface cultures of fully differentiated respiratory epithelium were infected with clinical strains of M. catarrhalisin vitro. 1 hour following infection, the cells were washed thoroughly and analysed by high-speed video microscopy and electron microscopy. M. catarrhalis was shown attached to ciliary tips and cilia in infected cultures demonstrated significant dyskinesia compared to uninfected control cell cultures. In summary, M. catarrhalis is isolated from nasal brushings in 10% of children referred for PCD diagnostic testing. M. catarrhalis attaches to the ciliary tip and causes secondary ciliary dyskinesia, possibly having implications for PCD diagnostic testing.