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Streptococcus pneumonia

Microbiology > Bacteriology > Gram-positive bacteria > Gram-Positive Cocci > Streptococci
1. Structure
a. Gram Positive, Catalase Negative, alpha-hemolytic
b. Shape: Slightly pointed (lancet shaped) diplococci but, can also be found as lone cocci or in a short chain.

2. Pathobiology:
a. facultative anaerobic organism
b. mesophilic
c. virulence factors
i. Caused by the chemical composition of the polysaccharide capsule: interferes with phagocytosis by preventing C3b opsonization of the bacterial cells.
1. More than 90 different serotypes are known which can differ in virulence, prevalence and drug resistant tendencies.
ii. Also contains protease which cleaves IgA allowing it to colonize and invade host mucosa
d. May have altered PBP, conferring resistance to penicillin. Resistance can be overridden in most tissues, but in specific spaces with limited antibiotic penetration (e.g. CSF), vancomycin or ceftriaxone is used.

3. Epidemiology
a. Typically resides asymptomatically in the nasopharynx of healthy carriers however, can become pathogenic in those with weakened immune systems, the elderly and children.
b. Individuals with sickle cell disease or splenectomies are particularly susceptible to strep pneumoniae infection as the spleen is important in clearing encapsulated bacteria
c. Incidence in adults peaks in midwinter and dips in the summer
d. Main cause of community acquired pneumonia and meningitis in adults, children and the elderly / Septicemia in HIV infected persons
i. Is a lobar pneumonia which generally affects the lower lobes and leads to the production of rust colored sputum
e. Spread from person to person through aerosol droplets

4. Disease manifestations
a. diagnostic methods
i. Gram stain is performed on the sputum of the infected patient.
ii. Blood Agar to test alpha-hemolysis
iii. Optochin sensitive
iv. Bile Solubility Test
b. Differential diagnosis
i. Other streptococcus bacteria can also exhibit alpha-hemolysis so organism must also exhibit bile or optochin sensitivity to be classified as S. pneumoniae
c. Most common bacterial Cause of many diseases (MOPS)
i. M- memingitis
ii. O- otitis media
iii. P- pneumonia
iv. S- sinusitis

d. Therapy
a. Beta lactams (Penicillins, cephalosporins)
b. for PCN  resistant strains due to altered Penicillin Binding Proteins: Vancomycin, Ceftriaxone

5. Prevention and control
a. Polysaccharide vaccine Vaccine
i. 23 valent polysaccharide (PPSV23)
ii. Since this does not contain protein, immune response is T cell independent
iii. Only causes IgM production which does not provide long lasting protection
b. Conjugated Vaccines
i. 7 valent vaccine and 13 valent vaccines (PCV-13) available
ii. Protein conjugation allows for a more robust T cell response
iii. Results in longer-lasting IgG response

Related concepts
  1. Steptococcus pneumoniae,
  2. alpha hemolysis,
  3. pneumonia,
  4. diplococci
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