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

Genus

Characteristics

Comments

Staphylococcus

Gram-positive cocci in clusters

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

Corynebaderium

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

Aerobic. Diphtheroids include anaerobic and aerotolerant organisms.

Moraxella

Gram-negative diplococci and diplobacilli

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

Haemophilus

Small, Gram-negative rods

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

Bacteroides

Small, pleomorphic, Gram-negative rods

Strict anaerobes.

Streptococcus

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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