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14.4: The Pneumococcus (Streptococcus pneumoniae)

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    Streptococcus pneumoniae, or the pneumococcus (see Fig. \(\PageIndex{1}\)), is a lancet-shaped (pointed like a lance) Gram-positive coccus 0.6-1.2 µm in diameter. They typically appear as a diplococcus, but occasionally appear singularly or in short chains. Pneumococci are frequently found as normal flora of the nasopharynx of healthy carriers. Pharyngeal colonization occurs in 40%-50% of healthy children and 20%-30% of healthy adults.

    Photomicrograph of a Gram stain of <i>Streptococcus pneumoniae</i> appearing as encapsulated Gram-positive diplicocci.

    Figure \(\PageIndex{1}\): Encapsulated Streptococcus pneumoniae. Streptococcus pneumoniae, or the pneumococcus, is a Gram-positive lanceolate coccus usually appearing as a diplococcus, but occasionally appearing singularly or in short chains. Pneumococci are frequently found as normal flora of the nasopharynx of healthy carriers. From 10% to 40% of adults carry the bacterium in the nasopharynx. In the U.S., they are the most common cause of community-acquired pneumonia requiring hospitalization, causing around 500,000 cases per year and usually occuring as a secondary infection in the debilitated or immunocompromised host. The pneumococci also cause over 7,000,000 cases of otitis media per year, are the leading cause of sinusitis in people of all ages, are responsible for 500,000 cases of bacteremia, and 3000 cases of meningitis, being the most common cause of meningitis in adults and children over 4 years of age.Note gram-positive encapsulated diplococci. The large cells with the dark red nuclei are while blood cells. (Copyright; Encapsulated Streptococcus pneumoniae. © Gloria Delisle and Lewis Tomalty, authors. Licensed for use, ASM MicrobeLibrary.)

    Worldwide, as well as in the U.S., S. pneumoniae remains the most common cause of community-acquired pneumonia, otitis media, bacteremia, and bacterial meningitis. In the U.S., pneumococci are the most common cause of community-acquired pneumonia requiring hospitalization, causing an estimated 500,000 cases per year and usually occuring as a secondary infection in the debilitated or immunocompromised host. The pneumococci also cause between 6 and 7 million cases of otitis media per year, are the leading cause of sinusitis in people of all ages, are responsible for 55,000 cases of bacteremia, and 3000 cases of meningitis, being the most common cause of meningitis in adults and children over 4 years of age.

    The capsule serves as the major virulence factor, enabling the pneumococcus to resist phagocytic engulfment, and glycopeptides from its Gram-positive cell wall can lead to excessive cytokine production and a massive inflammatory response.

    Contributors and Attributions

    • Dr. Gary Kaiser (COMMUNITY COLLEGE OF BALTIMORE COUNTY, CATONSVILLE CAMPUS)


    14.4: The Pneumococcus (Streptococcus pneumoniae) is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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