Taxos A & Taxos P test

Taxos A (bacitracin sensitivity testing)

This is a differential test used to distinguish between organisms sensitive to the antibiotic bacitracin and those not. Bacitracin is a peptide antibiotic produced by Bacillus subtilis. It inhibits cell wall synthesis and disrupts the cell membrane. This test is commonly used to distinguish between the b-hemolytic streptococci: Streptococcus agalactiae (bacitracin resistant) and Streptococcus pyogenes (bacitracin sensitive). The plate below was streaked with Streptococcus pyogenes; notice the large zone of inhibition surrounding the disk.

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Taxos P (optochin sensitivity testing)

This is a differential test used to distinguish between organisms sensitive to the antibiotic optochin and those not. This test is used to distinguish Streptococcus pneumoniae (optochin sensitive (pictured on the right below)) from other a-hemolytic streptococci (optochin resistant (Streptococcus mitis is pictured on the left below)).