Covers the general features of Streptococcus pneumoniae, including its Gram-positive lancet-shaped diplococci morphology, its growth needs, and key lab markers such as alpha-haemolysis, optochin sensitivity and bile solubility. It then moves through the capsule and other virulence factors, nasopharyngeal carriage and at-risk groups, the diseases it causes from pneumonia to sepsis, and diagnosis, treatment and vaccination. A closing table contrasts it with viridans streptococci, and several tables summarise virulence factors, vaccines and treatment options.
Topic 50 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 10 sections, about 124 words (4 min of reading), with 14 flashcards.
In this note
Streptococcus pneumoniae (Pneumococcus)
I. General Characteristics
II. Morphology and Structural Features
III. Virulence Factors
IV. Epidemiology
V. Diseases Caused
VI. Diagnosis
VII. Treatment
VIII. Prevention
IX. Differentiation from Viridans Streptococci
I. General Characteristics
Gram-positive, lancet-shaped diplococci (usually found in pairs).
Facultative anaerobe: Can grow aerobically and anaerobically, but prefers 5% CO₂ atmosphere.
α-hemolytic on blood agar → greenish discoloration due to partial hemolysis.
Optochin sensitive (differentiates from Viridans streptococci).
Bile soluble (gets lysed in bile).
Capsulated: The capsule is its major virulence factor.
Alpha-hemolysis and optochin sensitivity are key diagnostic features in the lab. Capsule is essential for escaping immune detection.
IV. Epidemiology
Reservoir: Human nasopharynx (normal flora in ~10–40%).
Transmission: Respiratory droplets, especially from asymptomatic carriers.
At-risk populations:
Children <5 yrs
Elderly
Splenectomised patients
Alcoholics, immunocompromised (HIV, organ transplants)
