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Quick Reference Environment: Facultative anaerobic cocci; require blood medium
Microorganism: Gram positive Spore former: YES Motile: NO
Susceptibility: Anyone Communicability: Infectious Exposure: Person to Person Incubation: As short as 1-3 days Primary Treatment: Penicillins Prognosis: Good with treatement Quarantine recommended: NO Use as a biological weapon: NO Identification
S. pneumoniae is a facultative anaerobic, Gram-positive bacterium found in pairs of cocci. It is by far the most common cause of bacterial pneumonia and meningitis. There are more than 80 known serotypes, In the U.S. mortality rates are still 5%-7%, even with treatment. laboratory indicators
Pathogenesis Encapsulation is the primary virulence factor, as the encapsulated cocci are antiphagocytic. In 1929, a famous experiment by Frederick Griffith, a medical officer at the Ministry of Health in London, showed that killed encapsulated cells mixed with live avirulent non-encapsulated cells caused disease in mice. Therefore, genetic exchange between dead and viable cells was possible. Alpha-haemolytic streptococci, such as S. pneumoniae, cause partial breakdown of blood. Colonies are often surrounded by a greenish halo. Pneumococci are present in a majority of the respiratory tracts of the population. In the elderly and other populations that may impaired ciliary activity, such as smokers, the organism may be allowed to reach pathogenic levels due to impaired drainage. Transmission is generally via water droplets from respiration.
Bacteria colonize in the nasopharyngeal epithelium and eventually migrate to the lower respiratory tract via aerosolization where they infect the alveoli. Due to Choline-Binding Proteins (CBP's), the pneumococcal cells are extremely resistant to phagocytosis, thus the growing colonies create an inflammatory response in the lungs. As the cells lyse in response to intercellular defense mechanisms and antibiotics, they release additional proteins that further increase tissue inflammation.
Manifestations Symptoms of bacterial pneumonia include fever, chills, general feeling of malaise, cough, and chest pain. Tests include a physical examination, phlegm test, blood test, urine test, and chest x-ray. Treatment Pneumococci are no longer considered to be susceptible to penicillin due to various resistance mutations, not in ß-lactamase, but in other associated proteins. For severe infections, Penicillin-G is used, but for mild infections, oral doses of Penicillin-V are administered. Prevention A recent finding suggests that 25% of S. pneumoniae isolated are resistant to one or more antibacterial treatments. For high-risk populations, a vaccine is available. | |
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