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  • What are some pathogenic bacteria that are part of the normal microbiota of the respiratory tract?
  • What virulence factors are used by pathogens to overcome the immune protection of the respiratory tract?

Signs and symptoms of respiratory infection

Microbial diseases of the respiratory system typically result in an acute inflammatory response. These infections can be grouped by the location affected and have names ending in “itis”, which literally means inflammation of . For instance, rhinitis is an inflammation of the nasal cavities, often characteristic of the common cold. Rhinitis may also be associated with hay fever allergies or other irritants. Inflammation of the sinuses is called sinusitis inflammation of the ear is called otitis . Otitis media is an inflammation of the middle ear. A variety of microbes can cause pharyngitis , commonly known as a sore throat. An inflammation of the larynx is called laryngitis . The resulting inflammation may interfere with vocal cord function, causing voice loss. When tonsils are inflamed, it is called tonsillitis . Chronic cases of tonsillitis may be treated surgically with tonsillectomy. More rarely, the epiglottis can be infected, a condition called epiglottitis . In the lower respiratory system, the inflammation of the bronchial tubes results in bronchitis . Most serious of all is pneumonia , in which the alveoli in the lungs are infected and become inflamed. Pus and edema accumulate and fill the alveoli with fluids (called consolidations). This reduces the lungs’ ability to exchange gases and often results in a productive cough expelling phlegm and mucus. Cases of pneumonia can range from mild to life-threatening, and remain an important cause of mortality in the very young and very old.

  • Describe the typical symptoms of rhinitis, sinusitis, pharyngitis, and laryngitis.

Smoking-associated pneumonia

Camila is a 22-year-old student who has been a chronic smoker for 5 years. Recently, she developed a persistent cough that has not responded to over-the-counter treatments. Her doctor ordered a chest radiograph to investigate. The radiological results were consistent with pneumonia. In addition, Streptococcus pneumoniae was isolated from Camila’s sputum.

Smokers are at a greater risk of developing pneumonia than the general population. Several components of tobacco smoke have been demonstrated to impair the lungs’ immune defenses. These effects include disrupting the function of the ciliated epithelial cells, inhibiting phagocytosis, and blocking the action of antimicrobial peptides. Together, these lead to a dysfunction of the mucociliary escalator effect. The organisms trapped in the mucus are therefore able to colonize the lungs and cause infections rather than being expelled or swallowed.

Key concepts and summary

  • The respiratory tract is divided into upper and lower regions at the epiglottis .
  • Air enters the upper respiratory tract through the nasal cavity and mouth, which both lead to the pharynx . The lower respiratory tract extends from the larynx into the trachea before branching into the bronchi , which divide further to form the bronchioles , which terminate in alveoli , where gas exchange occurs.
  • The upper respiratory tract is colonized by an extensive and diverse normal microbiota, many of which are potential pathogens. Few microbial inhabitants have been found in the lower respiratory tract, and these may be transients.
  • Members of the normal microbiota may cause opportunistic infections, using a variety of strategies to overcome the innate nonspecific defenses (including the mucociliary escalator) and adaptive specific defenses of the respiratory system.
  • Effective vaccines are available for many common respiratory pathogens, both bacterial and viral.
  • Most respiratory infections result in inflammation of the infected tissues; these conditions are given names ending in -itis , such as rhinitis , sinusitis , otitis , pharyngitis , and bronchitis .

Fill in the blank

Unattached microbes are moved from the lungs to the epiglottis by the _______ effect.

mucociliary escalator

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Many bacterial pathogens produce _______ to evade phagocytosis.

capsules

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The main type of antibody in the mucous membrane defenses is _______.

IgA

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_______ results from an inflammation of the “voice box.”

Laryngitis

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_______ phagocytize potential pathogens in the lower lung.

Alveolar macrophages

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Short answer

Explain why the lower respiratory tract is essentially sterile.

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Explain why pneumonia is often a life-threatening disease.

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Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
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