Streptococcus pneumoniae Hemolysis Pattern
No, Streptococcus pneumoniae is NOT beta-hemolytic—it is alpha-hemolytic, producing a characteristic greenish discoloration around colonies on blood agar plates.
Hemolysis Classification
S. pneumoniae is classified as an alpha-hemolytic organism, producing a greenish halo on blood agar plates that distinguishes it from beta-hemolytic streptococci 1
This alpha-hemolysis pattern is a key microbiological characteristic used by clinical laboratories to differentiate S. pneumoniae from Group A beta-hemolytic streptococci (S. pyogenes) 1
Mechanism of Alpha-Hemolysis
The greenish halo is caused by hydrogen peroxide produced by S. pneumoniae, which oxidizes oxy-hemoglobin (Fe+2) to met-hemoglobin (Fe+3), not by actual lysis of red blood cells 2
Studies using hydrogen peroxide knockout mutants (ΔspxB ΔlctO) demonstrated complete absence of the alpha-hemolytic halo, while pneumolysin knockout mutants (Δply) still produced the characteristic greenish zone 2
Under certain circumstances, pneumococci can produce zones of beta-hemolysis on blood-containing medium, suggesting a second hemolysin distinct from pneumolysin that can be inactivated by cholesterol 3
Clinical Distinction from Beta-Hemolytic Streptococci
Group A beta-hemolytic streptococci (S. pyogenes) are the most common cause of bacterial pharyngitis, requiring different diagnostic and treatment approaches than S. pneumoniae 1
Group A streptococci require throat culture on sheep blood agar plates with 90-95% sensitivity for detection 1
S. pneumoniae causes pneumonia, meningitis, sepsis, and otitis media—not pharyngitis—and requires identification through optochin sensitivity, bile solubility, or rapid coagglutination tests 1, 4
Laboratory Identification
Clinical microbiology laboratories report S. pneumoniae as "alpha-hemolytic streptococci" based on the greenish halo appearance 2
Definitive identification requires additional testing beyond hemolysis pattern, including optochin disk sensitivity, bile solubility testing, or Phadebact coagglutination, which can identify pneumococci within one minute 4