Relationships Between Oral Microecosystem and Respiratory Diseases Original paper

What was reviewed?

This paper is a comprehensive narrative review that examined the oral microecosystem as a biologically active interface between the upper aerodigestive tract and the lungs, with a specific focus on how oral microbial communities influence the development and progression of respiratory diseases. The authors reviewed epidemiological, microbiological, immunological, and molecular evidence to explain how oral microbiota, dental plaque biofilms, saliva, and oral immune defenses interact to shape respiratory infection risk. Rather than treating oral and respiratory systems as separate compartments, the review framed the oral cavity as a primary ecological source of the lung microbiome and a reservoir for respiratory pathogens under conditions of dysbiosis or impaired host defenses.

Who was reviewed?

The review integrated findings from studies involving healthy individuals, elderly populations, hospitalized and ventilated patients, individuals with poor oral health or periodontal disease, and patients with respiratory conditions including pneumonia, chronic obstructive pulmonary disease, cystic fibrosis lung disease, asthma, and lung cancer. Data were drawn from human clinical cohorts, bronchoalveolar lavage and sputum analyses, dental plaque and saliva sampling, as well as supporting in vitro and animal studies. This broad population base allowed the authors to link oral microbial composition and oral health status with respiratory disease susceptibility and severity.

What were the most important findings?

The review demonstrated that the oral microecosystem is the dominant source of microbes detected in the lower respiratory tract under both healthy and diseased states. Major microbial associations included oral streptococci, Neisseria, Prevotella, Fusobacterium, Veillonella, Porphyromonas gingivalis, Treponema denticola, and Tannerella forsythia, which were repeatedly identified in sputum and bronchoalveolar lavage samples from patients with pneumonia, COPD, and cystic fibrosis. The authors emphasized that dental plaque biofilms act as protected reservoirs where respiratory pathogens such as Streptococcus pneumoniae, Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumoniae, and Haemophilus influenzae can persist, adapt, and later seed the lower airways through aspiration or inhalation.

Importantly, the review detailed mechanistic pathways by which oral microbes and their products influence lung pathology. These included aspiration of bacteria and microbial components such as lipopolysaccharide, peptidoglycan, proteases, and toxins that modify respiratory epithelial surfaces, upregulate adhesion receptors, disrupt mucus barriers, and amplify inflammatory signaling. Oral pathogens such as P. gingivalis and F. nucleatum were shown to induce cytokines including IL-6, IL-8, TNF-α, and IL-1β in airway epithelial cells, promoting neutrophil recruitment, mucus hypersecretion, and tissue damage. The review also highlighted interspecies interactions, showing that oral microbes can enhance the virulence and persistence of respiratory pathogens through biofilm cooperation and immune modulation, while oral commensals such as lactobacilli and streptococci can exert antagonistic effects that limit pathogen colonization.

What are the greatest implications of this review?

For clinicians, this review establishes oral health and oral microbiome balance as modifiable determinants of respiratory disease risk. It supports integrating oral hygiene assessment and management into respiratory care pathways, particularly for vulnerable populations, and reinforces that preventing oral dysbiosis may reduce respiratory infections, inflammation, and disease progression.