Microbiota of the Respiratory Tract

The anterior nares are typically dominated by commensal Staphylococci and Corynebacterium, lipophilic Gram-positive bacteria that resemble skin microbiota. These organisms competitively inhibit potential pathogens, protecting the nasal cavity from harmful microbial colonization and contributing to the first line of defense in the upper respiratory tract.

Resident Streptococcus species in the nasal cavity and oropharynx produce antimicrobial peptides that inhibit pathogen growth. Additionally, commensal bacteria like Staphylococci and Corynebacterium competitively exclude potential pathogens through resource competition, while the broader microbial diversity in deeper nasal regions and the oropharynx supports mucosal immunity and suppresses pathogenic colonization.

Non-typeable Haemophilus influenzae adheres to mucus and non-ciliated epithelial cells, forming aggregates that mature into biofilms. These bacterial biofilms can contribute to chronic inflammation or localized infection when host defenses are weakened or mucosal barriers are disrupted, making the organism opportunistically pathogenic.

The lower respiratory tract harbors transient microbes that enter with inhaled air and from the oropharynx, including commonly detected genera such as Prevotella and Veillonella. These organisms, often anaerobic, survive in oxygen-rich environments by producing antioxidant enzymes and detoxifying enzymes to protect their cellular structures and DNA from reactive oxygen species.

The anterior nares are dominated by lipophilic Gram-positive bacteria like Staphylococci and Corynebacterium, while the oropharynx is the most diverse region of the upper respiratory tract, containing both Gram-positive and Gram-negative genera including Neisseria, Veillonella, and Prevotella. This greater diversity in the oropharynx supports broader immune protection and microbial balance.

Streptococcus pyogenes causes streptococcal pharyngitis by resisting immune clearance mechanisms in the upper respiratory tract. This pathogen can lead to serious complications such as scarlet fever or otitis media when it overcomes mucosal defenses and establishes infection in the pharynx or middle ear.

Bacteria in the lower respiratory tract, such as Prevotella and Veillonella, survive in oxygen-rich environments by producing antioxidant enzymes and detoxifying enzymes. These enzymes protect bacterial cellular structures and DNA from reactive oxygen species generated by host metabolism, allowing anaerobic organisms to persist in the lungs.