Streptococcus pneumoniae: Difference between revisions
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Streptococcus pneumoniae
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* 90+ serotypes, based on capsular polysaccharide that is bound to peptidoglycan |
* 90+ serotypes, based on capsular polysaccharide that is bound to peptidoglycan |
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* Lab identification is based on [[Has hemolysis pattern::α-hemolysis]] of blood agar (from pneumolysin), [[Has susceptibility to::optochin]] susceptibility, and bile salt solubility |
* Lab identification is based on [[Has hemolysis pattern::α-hemolysis]] of blood agar (from pneumolysin), [[Has susceptibility to::optochin]] susceptibility, and bile salt solubility |
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* Via transformation, bacteria can exchange genetic material with each other |
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=== Susceptibility testing === |
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* CLSI penicillin breakpoints for susceptibility changed in 2008 |
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** For meningitis: ≤0.06 μg/mL |
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** For other infections: ≤2 μg/mL |
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=== Antibiotic resistance === |
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* '''[[Penicillin]]''' resistance |
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** ''S. pneumoniae'' has 6 PBPs: 1A, 1B, 2A, 2B, 2X, and 3 |
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** Resistance in any of the PBPs can increase the MIC |
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** Mutations in PBP 2B are associated with low-level resistance |
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** Mutations in PBP 2X are associated with high-level resistance |
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* '''[[Macrolides|Macrolide]]''' resistance |
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** ''ermB'' encodes an enzyme that methylates the 23S subunit, blocking macrolides |
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** ''mefA'' encodes an efflux pump |
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== Epidemiology == |
== Epidemiology == |
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Revision as of 02:11, 3 October 2019
Microbiology
- Gram-positive, lancet-shaped diplococci
- 90+ serotypes, based on capsular polysaccharide that is bound to peptidoglycan
- Lab identification is based on α-hemolysis of blood agar (from pneumolysin), optochin susceptibility, and bile salt solubility
- Via transformation, bacteria can exchange genetic material with each other
Susceptibility testing
- CLSI penicillin breakpoints for susceptibility changed in 2008
- For meningitis: ≤0.06 μg/mL
- For other infections: ≤2 μg/mL
Antibiotic resistance
- Penicillin resistance
- S. pneumoniae has 6 PBPs: 1A, 1B, 2A, 2B, 2X, and 3
- Resistance in any of the PBPs can increase the MIC
- Mutations in PBP 2B are associated with low-level resistance
- Mutations in PBP 2X are associated with high-level resistance
- Macrolide resistance
- ermB encodes an enzyme that methylates the 23S subunit, blocking macrolides
- mefA encodes an efflux pump
Epidemiology
- Present worldwide
- Major cause of morbidity and mortality in children
- Leading cause of under-5 mortality worldwide
Pathophysiology
- Acquired by coughing and sneezing
- Asymptomatic carriage or colonization in the nasopharynx
- Invasion through epithelial cells into the bloodstream, using the PAF and pIg receptors
- Capsule and various proteins help it to evade immune system
Clinical Presentation
Asymptomatic carriage
- 4-10% in the general adult population, usually lasting several weeks
- Highest in children, up to 30-60% depending on the situation, lasting up to 6 months
Otitis media
Sinusitis
Bacteremia
Pneumonia
- Acute onset of cough (92%), fatigue (63%), shortness of breath (47%), and dyspnea (23%) with documented or subjective fever (92%), chills (77%), sweats, purulent sputum, and pleuritic chest pain (79%)
Meningitis
- Most common cause of meningitis in adults
- Acquired by hematogenous spread from nasopharynx, or direct invasion from sinuses
- May be secondary to otitis media or sinusitis
- CSF leaks and other defects predispose to infection
- Diagnostic yield in CSF decrease significantly 4 hours after administration of antibiotics
