A negative PYR test is demonstrated by which organism?

A negative PYR test is demonstrated by which organism?

• A. Enterococcus faecalis
• B. Enterococcus faecium
• C. Streptococcus pyogenes
• D. Viridans streptococci

Answer: (D)

The PYR test checks for the enzyme PYRase, which hydrolyzes a specific substrate to produce a color change. Organisms that have PYRase, such as Streptococcus pyogenes (Group A) and Enterococcus species (like Enterococcus faecalis and Enterococcus faecium), give a positive result with a pink/red color after adding the developer. Viridans streptococci, on the other hand, generally do not produce PYRase, so they do not hydrolyze the substrate and yield a negative result (no color change). Therefore, when the PYR test is negative, it points toward viridans streptococci among the listed organisms.

The PYR test checks for the enzyme PYRase, which hydrolyzes a specific substrate to produce a color change. Organisms that have PYRase, such as Streptococcus pyogenes (Group A) and Enterococcus species (like Enterococcus faecalis and Enterococcus faecium), give a positive result with a pink/red color after adding the developer.

Viridans streptococci, on the other hand, generally do not produce PYRase, so they do not hydrolyze the substrate and yield a negative result (no color change). Therefore, when the PYR test is negative, it points toward viridans streptococci among the listed organisms.