Bacterial Infections of the Respiratory System

Study Notes

Microorganisms are prevented from entering the respiratory system by hair in nasal passages, IgA antibodies, normal microbiota of the oropharynx, ciliary escalator, and alveolar macrophages.
Lower respiratory tract is normally sterile.
Bacterial respiratory infections occur due to inhalation of fine droplets from the mouth into the lungs.
Periodontal bacteria can be drawn into the lower respiratory tract, leading to pneumonia and exacerbating conditions like COPD.
Periodontal disease is linked to pneumonia, COPD, and bronchitis.
Periodontal pathogens may contribute to the pathology of COPD.
Smoking damages gingiva and oral health, increasing gum pockets and attachment loss, and contributing to COPD.

Viral infections are the majority of URTI, often mild and self-limiting.
Bacteria can cause primary or secondary URTI (superinfection of viral infection).
Otitis media: infection of the middle ear, often viral or bacterial. Caused by bacteria spreading from throat/sinus infections via the eustachian tube.
Sinusitis: inflammation of paranasal sinuses (commonly maxillary). Usually viral, but can lead to bacterial superinfection. Sinus obstructions block drainage, leading to mucous accumulation.
Odontogenic sinusitis: sinusitis caused by dental or dentoalveolar infection affecting the sinus floor.

Viruses are the most common cause of pharyngitis.
Bacterial pharyngitis (strep throat) is less common.
Strep throat is often caused by Streptococcus pyogenes; diagnosed clinically through Centor Criteria.

Pneumonia: inflammation of lung alveoli.
Community-acquired pneumonia: pneumonia developed outside of a healthcare facility.
Healthcare-associated pneumonia: pneumonia developed in a healthcare facility.
Predisposing factors include poor oral health (periodontal disease) which increases rates of oral streptococci and anaerobes in pneumonia patients, and a link to pneumonia mortality.
Symptoms of pneumonia include cough, fever, chest pain, shortness of breath, and sputum.
Bacterial causes include Streptococcus pneumoniae, Haemophilus influenzae, Klebsiella pneumoniae, and others.

Opportunistic infections are infections caused by organisms that don't normally cause illness in healthy people.
People with weakened immune systems (HIV/AIDS, transplants, cancer, autoimmune conditions, cystic fibrosis, diabetes, etc.) are more susceptible.
Pseudomonas aeruginosa is an example of an opportunistic infection in the lower respiratory tract, often encountered in cystic fibrosis.

Pseudomonas aeruginosa: Gram-negative bacilli, aerobic, common environmental bacteria.
Mycobacterium tuberculosis: Obligate aerobic, acid-fast resistant bacteria causing slow-growing tuberculosis, a long-term infection, common in underdeveloped countries. Spread by respiratory aerosols.
Klebsiella pneumoniae: gram-negative bacilli causing pneumonia.

Antibiotic resistance: bacteria becoming resistant to antibiotics due to mutations, gene transfer, and other factors.
Multidrug-resistant organisms (MDROs) pose a threat to patient treatment.