Pneumococcus and viridans streptococci vs Group A and Group B Streptococcus
How to tell Pneumococcus and viridans streptococci and Group A and Group B Streptococcus apart when a board question makes them look alike.
Alpha hemolysis splits by optochin; beta hemolysis splits by Group A pharyngitis versus Group B neonate.
Side by side
Alpha-hemolytic streptococci: pneumococcus is optochin-sensitive/bile-soluble and encapsulated; viridans is optochin-resistant oral flora.
Beta-hemolytic Lancefield groups: Group A causes pharyngitis/skin disease; Group B causes neonatal sepsis/meningitis.
Capsule drives pneumococcal virulence; oral adherence/biofilm patterns drive viridans dental/endocarditis clues.
Group A uses M protein and pyogenic toxins; Group B colonizes genital tract and causes neonatal invasive disease.
Optochin-sensitive alpha hemolysis points pneumococcus; optochin-resistant alpha hemolysis after dental work points viridans.
Bacitracin-sensitive beta hemolysis points Group A; CAMP-positive beta hemolysis in neonate points Group B.
The trap
Hemolysis pattern is only the start. Within alpha-hemolytic colonies, optochin sensitivity decides: optochin-sensitive plus bile-soluble equals Streptococcus pneumoniae (lancet-shaped diplococci, encapsulated, common in community-acquired pneumonia, meningitis, otitis media, and sinusitis); optochin-resistant plus bile-insoluble equals viridans group (subacute bacterial endocarditis on previously damaged valves after dental procedures, S sanguinis on damaged valves and S mutans for dental caries). Within beta-hemolytic colonies, bacitracin decides: bacitracin-sensitive equals Group A Strep / S pyogenes (pharyngitis, scarlet fever, post-strep rheumatic fever, post-strep glomerulonephritis, necrotizing fasciitis); bacitracin-resistant plus CAMP-test positive plus hippurate-positive equals Group B Strep / S agalactiae (neonatal meningitis and sepsis; routinely screen pregnant women at 35 to 37 weeks).
The repair move
For streptococci, sort hemolysis first, then the one lab test and clinical setting.
Try a free question
CoreAn alpha-hemolytic, optochin-sensitive, bile-soluble lancet-shaped diplococcus with a polysaccharide capsule causes lobar pneumonia and meningitis. Which organism is most likely?
Show answer and explanation
Answer: A. Streptococcus pneumoniae. S pneumoniae is alpha-hemolytic, optochin-sensitive, bile-soluble, encapsulated, and lancet-shaped.
Why the other choices are tempting
- B. Viridans streptococci are alpha-hemolytic but optochin-resistant and linked to dental caries/endocarditis.
- C. Group A Streptococcus is beta-hemolytic and bacitracin-sensitive.
- D. Group B Streptococcus is beta-hemolytic and causes neonatal sepsis/meningitis.
- E. Enterococcus is group D and grows in bile/esculin with different clinical anchors.
Flashcards
Tap a card to flip it.
What is the fastest separator for Pneumococcus and viridans streptococci vs Group A and Group B Streptococcus?
Alpha hemolysis splits by optochin; beta hemolysis splits by Group A pharyngitis versus Group B neonate.
What clue should make you choose Pneumococcus and viridans streptococci?
Alpha-hemolytic streptococci: pneumococcus is optochin-sensitive/bile-soluble and encapsulated; viridans is optochin-resistant oral flora.
Quick answers
What is the fastest way to tell Pneumococcus and viridans streptococci from Group A and Group B Streptococcus?
Alpha hemolysis splits by optochin; beta hemolysis splits by Group A pharyngitis versus Group B neonate.
What is the key clue for Pneumococcus and viridans streptococci?
Alpha-hemolytic streptococci: pneumococcus is optochin-sensitive/bile-soluble and encapsulated; viridans is optochin-resistant oral flora.
What is the key clue for Group A and Group B Streptococcus?
Beta-hemolytic Lancefield groups: Group A causes pharyngitis/skin disease; Group B causes neonatal sepsis/meningitis.
What is the common trap with Pneumococcus and viridans streptococci vs Group A and Group B Streptococcus?
Hemolysis pattern is only the start. Within alpha-hemolytic colonies, optochin sensitivity decides: optochin-sensitive plus bile-soluble equals Streptococcus pneumoniae (lancet-shaped diplococci, encapsulated, common in community-acquired pneumonia, meningitis, otitis media, and sinusitis); optochin-resistant plus bile-insoluble equals viridans group (subacute bacterial endocarditis on previously damaged valves after dental procedures, S sanguinis on damaged valves and S mutans for dental caries). Within beta-hemolytic colonies, bacitracin decides: bacitracin-sensitive equals Group A Strep / S pyogenes (pharyngitis, scarlet fever, post-strep rheumatic fever, post-strep glomerulonephritis, necrotizing fasciitis); bacitracin-resistant plus CAMP-test positive plus hippurate-positive equals Group B Strep / S agalactiae (neonatal meningitis and sepsis; routinely screen pregnant women at 35 to 37 weeks).