Which organism is sensitive to bacitracin, indicating a possible infection?

Bacitracin sensitivity is a key characteristic used in the laboratory to identify specific bacterial infections caused by certain streptococcal species. Streptococcus pyogenes, also known as Group A Streptococcus, is the organism that exhibits sensitivity to bacitracin. When cultured on blood agar, if S. pyogenes is present, it will show a zone of inhibition around a bacitracin disk, confirming its identity.

This sensitivity helps clinicians differentiate S. pyogenes from other beta-hemolytic streptococci, particularly Streptococcus agalactiae (Group B Streptococcus), which is resistant to bacitracin. Therefore, if a patient presents with symptoms of a streptococcal infection and the laboratory tests show bacitracin susceptibility, it strongly suggests an infection with S. pyogenes.

In contrast, Streptococcus pneumoniae is not tested for bacitracin sensitivity as it is classified under alpha-hemolytic streptococci and does not exhibit this susceptibility. Staphylococcus aureus is a different genus altogether, and its identification typically relies on other tests such as coagulase testing rather than bacitracin sensitivity. Thus, the bacitracin sensitivity test