Diagnosis
Usually, a throat swab is taken to the laboratory for testing. A Gram stain is performed to show Gram-positive cocci in chains. Then, the organism is cultured on blood agar with an added bacitracin antibiotic disk to show beta-hemolytic colonies and sensitivity (zone of inhibition around the disk) for the antibiotic. Culture on non-blood containing agar then, perform catalase test, which should show a negative reaction for all Streptococci. S. pyogenes is CAMP (not to be confused with cAMP) and hippurate tests negative. Serological identification of the organism involves testing for the presence of group A specific polysaccharide in the bacterium's cell wall using the Phadebact test.
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