Investigation of the Number of Oral Bacteria in Patients with Chronic Obstructive Pulmonary Disease, Asthma, and Asthma and Chronic Obstructive Pulmonary Disease Overlap

Objective Bacteria in the airways are reportedly involved in the pathogenesis of chronic obstructive pulmonary disease (COPD) and asthma. In addition, oral bacteria are thought to contribute to respiratory diseases by migrating to the airway. Therefore, we investigated whether or not the number of oral bacteria influences COPD, asthma, and asthma and COPD overlap (ACO). Methods We analyzed the correlations between the number of oral bacteria and clinical variables, such as pulmonary function tests, in patients with COPD, asthma, and ACO whose condition was stable and who visited our center from August 2019 to December 2020. The number of oral bacteria was assessed using the dielectrophoretic impedance measurement method. Results In patients with COPD (n = 50), the number of oral bacteria was significantly negatively correlated with the percentage predicted forced expiratory volume in one second (%FEV1), percentage peak expiratory flow, and percentage forced vital capacity but was not correlated with the COPD Assessment Test. In patients with asthma (n = 32), it was significantly negatively correlated with the FEV1 percentage and with the increase in FEV1 in the reversibility test but not with fractional exhaled nitric oxide. In patients with ACO (n = 39), we found no significant correlation between the number of oral bacteria and any clinical variable. Conclusion The results suggest that the number of oral bacteria is associated with both lung capacity and airflow obstruction in patients with COPD and with airflow obstruction in patients with asthma.