About Streptococcus Pneumoniae

Bacteriology

S. pneumoniae is a gram positive, lancet-shaped cocci bacterium approximately 0.5 to 1.25 micrometers in diameter. The colonies are usually seen as diplococci, but they also appear in long chains or single cells in culture. Cultured in blood agar, S. pneumoniae is best grown in 5 percent added carbon dioxide, and it leaves the circular, green zones seen from hemolytic bacteria.

The cell wall of the S. pneumoniae bacterium is a thick, peptidoglycan with teichoic acid (characterized by the gram positive staining) layer. The bacteria also have pili that extend from the peptidoglycan layer, which are small hair-like structures that enable the cell to attach to the upper respiratory tissue. Another part of the bacteria's virulence factors is a capsule that enables it to resist phagocytosis, the process in which immune cells destroy harmful microbes in the body.

Streptococcus pneumoniae attaches to the respiratory tract of almost 40 percent of the human population. It also infects animals such as rabbits, monkeys, horses and mice. The disease symptoms are caused by the response from the immune system. If the bacteria are able to reach the lower respiratory tract, cytokines flow to the area of infection and cause extensive inflammation. The bacteria also travel to the alveoli where it uses choline for metabolism.

Streptococcus pneumoniae is a part of the normal flora in the human body. Children carry the bacteria in the nasopharynx without any symptoms unless it travels to other areas like the ear. Most children under the age of 5 will experience ear infections due to S. pneumoniae. Approximately 25 percent of pneumonia cases are caused by Streptococcus pneumoniae. The bacteria have also acquired increased resistance to penicillin and cephalosporin antibiotics.

There are more than 90 different capsule variations of Streptococcus pneumoniae. Current vaccinations available protect against 85 to 90 percent of the variants that cause disease. Vaccination is recommended for those who are immunocompromised such as the elderly. Some variant types are also included in vaccinations for infants to protect against septicemia and meningitis.