Which susceptibility test identifies group A β-hemolytic streptococci?

The susceptibility test that identifies group A β-hemolytic streptococci is based on bacitracin sensitivity. Group A streptococci, primarily Streptococcus pyogenes, are known to be sensitive to bacitracin, which allows for differentiation from other groups like group B streptococci (Streptococcus agalactiae), which are resistant.

When performed, a bacitracin disk is placed on an agar plate inoculated with the test organism. If the organism is sensitive to bacitracin, a zone of inhibition will appear around the disk, indicating susceptibility. This test is a straightforward and effective method for distinguishing group A β-hemolytic streptococci from other streptococcal species.

The other tests mentioned, such as furazolidone susceptibility, coagulase testing, and modified oxidase testing, are not specific for identifying group A β-hemolytic streptococci. Furazolidone susceptibility is more related to certain Gram-negative bacteria. Coagulase testing is primarily used to differentiate Staphylococcus aureus from other staphylococci, particularly for identifying pathogenic strains. Modified oxidase testing is generally used for the identification of certain Gram-negative bacteria,