Microcheck 232

Except in parts of the upper respiratory tract, the respiratory system is free of a normal microbial flora. The upper respiratory tract flora is highly diverse, including aerobes, anaerobes, facultative anaerobes, and aerotolerant bacteria. Although most of them are of low virulence, these organisms can sometimes cause disease.

■ What are some possible advantages to the body of providing a niche for normal flora in the upper respiratory tract?

■ How can strict anaerobes exist in the upper respiratory tract?

Table 23.1 Normal Flora of the Respiratory System





Gram-positive cocci in clusters

Commonly includes the potential pathogen Staphylococcus aureus, inhabiting the nostrils. Facultative anaerobes.


Pleomorphic, Gram-positive rods; non-motile; non-spore-forming

Aerobic. Diphtheroids include anaerobic and aerotolerant organisms.


Gram-negative diplococci and diplobacilli

Aerobic. Some resemble pathogenic Neisseria species such as N. meningitidis.


Small, Gram-negative rods

Facultative anaerobes. Commonly include the potential pathogen H. influenzae.


Small, pleomorphic, Gram-negative rods

Strict anaerobes.


Gram-positive cocci in chains

a (especially viridans), b, and gtypes; the potential pathogen, S. pneumoniae is often present. Aerotolerant.

23.3 Bacterial Infections of the Upper Respiratory System 565

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