Cocos Gram-positivos

Streptococcus pneumoniae

Q: How to identify Streptococcus pneumoniae in the lab?

Streptococcus pneumoniae is identified through catalase-negative, alpha-hemolytic, susceptible to optochin (p disk), bile-soluble.

Q: What are the intrinsic resistances of Streptococcus pneumoniae?

This organism is naturally resistant to aztreonam, colistin, aminoglycosides and sulfonamides have no activity. These drugs should not be reported as susceptible.

Q: Where is Streptococcus pneumoniae commonly found?

It is typically associated with community-acquired pneumonia, otitis media, sinusitis, meningitis.

Lancet-shaped Gram-positive diplococci

Identification & Growth

Identification

Catalase-negative, alpha-hemolytic
Susceptible to optochin (P disk), bile-soluble

Growth Conditions

Blood agar with 5% CO₂: mucoid, umbilicate, alpha-hemolytic colonies
35 °C, 18–24 h; autolysis after 48 h

Clinical Significance

Community-acquired pneumonia, otitis media, sinusitis, meningitis

Intrinsic Resistance

Aztreonam, colistin, aminoglycosides and sulfonamides have no activity

Bench Alerts

Oxacillin 1 µg screening disk: a zone < 20 mm requires a penicillin MIC
Interpretation of penicillin susceptibility depends on the infection site (meningeal vs. non-meningeal, per EUCAST breakpoint tables v16.1)
Use Mueller-Hinton agar supplemented with blood, incubated in CO₂, for disk diffusion

Clinical Notes

Clinical presentations

Leading bacterial cause of community-acquired pneumonia, acute otitis media, and sinusitis.
Causes severe bacterial meningitis in adults and children, with high lethality and neurologic sequelae.
Causes occult bacteremia and sepsis, particularly in splenectomized and immunosuppressed patients.

Specimens and collection

Good-quality sputum (few epithelial cells, many leukocytes) must be processed promptly, as the organism is autolytic and fragile.
CSF should be transported immediately at room temperature, not refrigerated, to preserve viability.
Blood cultures should be obtained before antibiotic therapy in every patient with suspected severe pneumonia or meningitis.

Epidemiology and at-risk populations

Children under 2 years and adults over 65 have the highest incidence of invasive pneumococcal disease.
Pneumococcal conjugate vaccination has significantly reduced invasive disease from vaccine serotypes in pediatric populations.
Functional or anatomic asplenia, HIV, and chronic lung disease substantially increase invasive infection risk.

Resistance and therapeutic implications

Penicillin resistance occurs via altered penicillin-binding proteins (PBPs) and is dose- and site-dependent (meningitis requires stricter categorization).
Macrolide resistance is common and may be mediated by efflux (mefA) or ribosomal methylation (ermB), the latter conferring high-level resistance.
EUCAST/BrCAST recommend distinct penicillin categorization for meningitis versus other infections due to limited CSF penetration.

Bench and reporting notes

Alpha-hemolytic colonies with central depression ("coin-shaped") and optochin susceptibility (disk) support presumptive identification.
Positive bile solubility differentiates S. pneumoniae from optochin-resistant alpha-hemolytic viridans streptococci.
CSF and blood isolates require penicillin susceptibility testing with site-specific categorization.

Sources

Educational decision-support content. It does not replace laboratory validation, current guidelines or review by the responsible professional.

FAQ: Frequently Asked Questions

How to identify Streptococcus pneumoniae in the lab?