(556) Evaluation of total bacterial 16S load and inflammation during IV-treated PEx in infrequent and frequent exacerbators

Background: CF pulmonary exacerbations (PEx) have a negative impact on quality of life and are associated with accelerated lung function decline and reduced survival. The number of previous-year PEx has been characterised as the strongest independent risk factor for future PEx for people with CF (pwCF). However, the underlying drivers of frequent exacerbations have not been investigated. In this study we compared sputum total bacterial 16S load, P. aeruginosa (PA) load, and inflammatory markers during a PEx between pwCF and a history of infrequent or frequent PEx.

Methods: Adults (aged ≥18 years) with CF admitted for intravenous antibiotics (IVabs) for a PEx were recruited in a single centre observational study. Participants were classified as infrequent or frequent exacerbators depending on the number of IV-treated PEx experienced in the previous year (< 2 or ≥2). Baseline demographics, lung function and chronic culture data were obtained. Matched sputum samples were collected from participants on day 0 (D0), between day 3-5 (D3-5) and at the end of treatment (EOT) of a PEx. Microbial DNA was extracted from sputum and total bacterial 16S load and PA load were determined by qPCR (LightCycler®) using a probe-based detection system targeting 16S rRNA and oprL genes. Sputum IL-1β and IL-8 were measured by multiplex assay (ELLA Simple Plex). Correlations between bacterial qPCR data and sputum inflammatory markers were assessed.

Results: A total of 29 pwCF were enrolled in the study (14 infrequent and 15 frequent exacerbators) and 75 sputum samples were analysed from D0 (n=28), D3-5 (n=25) and EOT (n=22). No differences in participant baseline characteristics were identified between cohorts including sex, age, ppFEV₁ and ≥1 F508del mutation. Frequent exacerbators had a significantly higher total bacterial 16S copy number in sputum on D3-5 and EOT and did not experience a significant reduction in total bacterial 16S copy number during IVabs. In contrast, a significant reduction in total bacterial 16S copy number between D0 and D3-5 of IVabs was experienced by infrequent exacerbators. No significant difference in oprL copy number was observed between cohorts during IVabs. Frequent exacerbators had significantly higher levels of IL-1β in sputum on D3-5 and EOT, and IL-8 in sputum at EOT. Total bacterial 16S copy number displayed a significant positive correlation with sputum inflammatory markers.

Conclusions: Frequent exacerbators had a higher total bacterial 16S load and levels of inflammatory markers in sputum during, and at the end of IV treatment of a PEx compared to infrequent exacerbators. The increased total bacterial load in this patient cohort was not a result of a higher P. aeruginosa load. Persistent bacterial infection and unresolved inflammation post-PEx are potential underlying drivers of frequent PEx.

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