Clinical microbiology – cause of streptococcal pharyngitis Which gram-positive bacterium is the classic etiologic agent of acute bacterial pharyngitis (sore throat) in the community?

Introduction / Context:
Acute bacterial pharyngitis is most commonly caused by group A beta-hemolytic Streptococcus (Streptococcus pyogenes). Correct identification guides therapy and prevents complications such as rheumatic fever and post-streptococcal glomerulonephritis.

Given Data / Assumptions:

• Organisms listed include both gram-positive and gram-negative genera.
• We seek the classic community cause of bacterial sore throat.

Concept / Approach:

Streptococcus pyogenes adheres to pharyngeal epithelium, produces pyrogenic exotoxins, and elicits pharyngeal inflammation and exudates. Neisseria (gonorrhoeae) can cause pharyngitis but is not the typical community agent. Staphylococcus aureus is less common as a sole cause of acute streptococcal-type pharyngitis.

Step-by-Step Solution:

Verification / Alternative check:

Rapid antigen detection tests and throat cultures routinely target group A streptococci, reflecting their predominance.

Why Other Options Are Wrong:

• Neisseria: occasional; not classic in general populations.
• Staphylococcus: can colonize or cause tonsillitis but is not the canonical agent.
• Mycobacterium/Corynebacterium: not typical acute pharyngitis agents (diphtheria presents differently).

Common Pitfalls:

• Assuming any gram-positive coccus equals “strep throat”; specific group A strep is implied.

Final Answer:

Streptococcus