Streptococcus pneumoniae

Categorization
Cell Wall: Gram Positive Shape: Cocci, Lancet-shaped Diplococci)
Biochemistry: Catalase Negative Metabolism: Microaerophilic
Streptococcal subclassification: No Lancefield Antigen, alpha-hemolytic
Optochin sensitivity used to distinguish from Viridans streptococci which are resistant
Virulence Factors
  • Capsule: Polysaccharide capsule protects organism from phagocytosis and more than 90 capsular serotypes exist.
Clinical Consequences
  • Overview
    • S. pneumoniae is a part of the normal nasopharyngeal flora in many individuals and generally does not cause disease in most adults. However, the organism can spread into anatomically contiguous areas such as the lung or ear when certain normal host defense processes are impaired. For example, prior viral infection, smoking or alcohol consumption, bronchial obstruction, or reduced cough reflex may facilitate spread of the organism. Hematogenous spread to the meninges or joints, usually from respiratory infections, can subsequently occur
  • Lung
    • S. pneumonia is the most common cause of Community-acquired pneumonia in adults. Often a Lobar pneumonia occurs that appears as a white infiltrate on chest radiography that is limited to a single lobe or lung segment. High fevers along with a productive cough of purulent sputum is frequently observed. Sputum may contain large number of diplococci upon gram stain. Pleuritic chest pain signals the spread of infection to the pleura and may result in empyema.
  • Ear and Nasopharyngeal Sinuses
    • S. pneumoniae is the most common cause of otitis media and sinusitis in children
  • Meninges
    • Most common cause of bacterial meningitis in adults and rising in children due to successful vaccination against H. influenzae
  • Bacteremia and Sepsis:
    • Especially consider in asplenic patients
Immunity
  • Humoral immunity against the S. pneumoniae polysaccharide capsule is protective; however, there are more than 90 different serotypes and immunity from one is not protective against others.
Vaccination
  • Adults: A vaccine containing the 25 most common capsular antigens is used especially for susceptible populations (Elderly, asplenic, or immunocompromised patients)
  • Children: A conjugate vaccine of the seven most common capsular antigens is used for children
Treatment
  • Early penicillins such as amoxicillin or alternatively erythromycin