Bacterial Load in Bronchial Washing Fluid Samples of Patients Undergoing Proton Pump Inhibitor Therapy: A Retrospective Observational Study Using Fluorescein as a Marker of Micro-Aspiration

Background: Proton pump inhibitors (PPIs) have been associated with lung dysbiosis and increased respiratory risk. Micro-aspiration is a proposed mechanism, but reliable biomarkers remain elusive. This study evaluates the potential of fluorescein as a biomarker of micro-aspiration and PPI-associated pulmonary risk. Methods: We conducted a retrospective analysis of 137 bronchial washing fluid samples from patients with pulmonary conditions to assess microbial colonization in relation to PPI use. Bacterial burden was determined by culture and PCR and categorized as 0, 1 or ≥2 pathogens. Micro-aspiration was evaluated by quantifying fluorescein-laden macrophages in bronchoalveolar lavage following oral fluorescein administration. Associations between PPI use, fluorescein levels and pathogen burden were analyzed using adjusted ordinal regression models. Results: PPI use was associated with higher odds of increased pathogen burden, though not statistically significant (OR = 1.40, 95% CI: 0.71–2.75, p = 0.33). Fluorescein-laden macrophages were higher in PPI users (41.5 versus 31.2 ng/mL), but showed no meaningful correlation with pathogen load (p = 0.09). Corticosteroid therapy was significantly associated with Gram stain results (OR = 2.37, 95% CI: 1.12–5.15, p = 0.03). Conclusions: These findings suggest a potential link between PPI use and airway colonization. Fluorescein shows promise as a biomarker for micro-aspiration, but its clinical utility requires further validation.