What is the use of trimethoprim-sulfamethoxazole (SXT) disks in relation to streptococci?

The use of trimethoprim-sulfamethoxazole (SXT) disks in relation to streptococci primarily serves to differentiate β-hemolytic streptococci, particularly Streptococcus pyogenes (group A streptococci) from other Group β streptococci, like Streptococcus agalactiae (group B streptococci).

When using the SXT disk diffusion method, if an organism is susceptible to trimethoprim-sulfamethoxazole, this can help indicate that the organism is not a group A or potentially other resistant strains. This differentiation is clinically significant as it assists in the appropriate identification and treatment of streptococcal infections, ensuring that healthcare practitioners can effectively manage and treat the specific types of streptococcal bacteria present in a patient.

In summary, the test is a valuable tool for distinguishing the microbial profile of β-hemolytic streptococci, which is crucial for accurate diagnosis and treatment.