Non-A and non-B β-hemolytic streptococci generally show which reactions to bacitracin and SXT?

Non-A and non-B β-hemolytic streptococci, commonly classified as Group C and Group G streptococci, have variable reactions to bacitracin and sulfonamide trimethoprim (SXT). Generally, these species show resistance to bacitracin, which is a distinguishing factor when differentiating them from Group A streptococci that are sensitive to it. In contrast, sensitivity to SXT can be observed in some cases, but it is not universal, leading to variability in responses.

The selected answer correctly reflects this variability, stating that these streptococci may either be susceptible or resistant to bacitracin while consistently showing susceptibility to SXT. This adaptability is critical for identification in a laboratory setting, as the reactions provide insights into the specific species of streptococci present and their classifications.

This understanding is significant since clinicians rely on these biochemical tests for accurate diagnosis and treatment decisions. The recognition that non-A and non-B β-hemolytic streptococci can exhibit different patterns is essential for microbiological evaluation and helps guide therapeutic choices.