Streptococcus pyogenes is identified as Group A strep by sensitivity to which antimicrobial agent?

Streptococcus pyogenes is identified as Group A strep by sensitivity to which antimicrobial agent?

• A. Bacitracin sensitivity
• B. Optochin sensitivity
• C. Coagulase test
• D. Oxidase test

Answer: (A)

Group A Streptococcus (Streptococcus pyogenes) is classically identified by its sensitivity to bacitracin. In the lab, when a bacitracin disk is placed on a culture of beta-hemolytic streptococci, Streptococcus pyogenes shows inhibition of growth around the disk, producing a clear zone. This bacitracin sensitivity helps distinguish Group A strep from other beta-hemolytic streptococci that are typically resistant, making it a rapid presumptive test for this organism. Optochin sensitivity identifies Streptococcus pneumoniae, not Group A strep. The coagulase test differentiates Staphylococcus aureus from other staphylococci, not streptococcal groups. The oxidase test is used for certain Gram-negative organisms and some other species, but it’s not used to identify Group A strep.

Group A Streptococcus (Streptococcus pyogenes) is classically identified by its sensitivity to bacitracin. In the lab, when a bacitracin disk is placed on a culture of beta-hemolytic streptococci, Streptococcus pyogenes shows inhibition of growth around the disk, producing a clear zone. This bacitracin sensitivity helps distinguish Group A strep from other beta-hemolytic streptococci that are typically resistant, making it a rapid presumptive test for this organism.

Optochin sensitivity identifies Streptococcus pneumoniae, not Group A strep. The coagulase test differentiates Staphylococcus aureus from other staphylococci, not streptococcal groups. The oxidase test is used for certain Gram-negative organisms and some other species, but it’s not used to identify Group A strep.