Which organism may yield a delayed positive PYR reaction?

Which organism may yield a delayed positive PYR reaction?

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

Answer: (D)

The PYR test detects the enzyme PYRase, which cleaves a specific substrate to yield a color change. Some organisms show a rapid, strong color change, while others may only turn positive after extended incubation due to slower enzyme expression. Micrococcus can exhibit this delayed PYR positivity, so a result read later may become positive. The other organisms in the list typically produce either a rapid PYR-positive reaction (such as certain streptococci) or are not PYR-positive, so they do not commonly show delayed positivity. Thus, delayed PYR positivity is a characteristic that can be seen with Micrococcus under longer incubation.

The PYR test detects the enzyme PYRase, which cleaves a specific substrate to yield a color change. Some organisms show a rapid, strong color change, while others may only turn positive after extended incubation due to slower enzyme expression. Micrococcus can exhibit this delayed PYR positivity, so a result read later may become positive. The other organisms in the list typically produce either a rapid PYR-positive reaction (such as certain streptococci) or are not PYR-positive, so they do not commonly show delayed positivity. Thus, delayed PYR positivity is a characteristic that can be seen with Micrococcus under longer incubation.