Biochemical Tests (2)

Microdase Test (Principle)

______________: Differentiates Staphylococcus from Micrococcus by detecting the oxidase enzyme. A reagent disk with TMPD in DMSO turns blue or purple if oxidase is present, indicating Micrococcus.

Microdase Test (expected results)

_______________:

• Positive: Development of blue to purple-blue color within 2 minutes time

• Negative: No color change (white to gray color remains).

Novobiocin Susceptibility Test (Principle)

______________: Determines if bacteria are sensitive or resistant to novobiocin. A clear zone shows sensitivity; no zone shows resistance. It helps identify novobiocin-resistant Staphylococcus saprophyticus.

Novobiocin Susceptibility Test (Expected results)

______________:

• Positive – A zone of inhibition greater than 16mm indicates that the organism is sensitive to the antibiotic.

• Negative – A zone of inhibition less than or equal to 16mm is indicative of novobiocin resistance.

Optochin Susceptibility Test (Principle)

_______________: Identifies S. pneumoniae by placing an optochin disk on the culture. A clear zone means sensitive (S. pneumoniae), while no zone means resistant (other streptococci).

Optochin Susceptibility Test (Expected results)

_______________:

• Positive Test: Zone of inhibition is 14 mm or greater in diameter with 6 mm disk.

• Negative Test: No zone of inhibition or a zone of inhibition of <14mm diameter.

Optochin Susceptibility Test (Quality control)

_______________:

• Positive: Streptococcus pneumoniae

• Negative: Streptococcus pyogenes 

PYR Test (Principle)

______________: Identifies certain bacteria by detecting the pyrrolidonyl arylamidase enzyme. A red or purple color after adding reagent indicates a positive result.

PYR Test (Expected results)

_______________:

• Positive: Bright pink or cherry-red color within 1-2 minutes.

• Negative: No color change or a blue color due to a positive indole reaction.

PYR Test (Quality control)

_______________:

Positive Control: Enterococcus faecalis, Streptococcus pyogenes

Negative Control: Streptococcus agalactiae

Salt Tolerance Test (Principle)

_______________: Checks if bacteria can grow in 6.5% NaCl. Salt-tolerant organisms, like Enterococcus, grow and produce acid, turning the broth from purple to yellow.

Salt Tolerance Test (Expected results)

________________:

• Positive:   Visible turbidity in the broth, with or without a color change from purple to yellow. Note: Turbidity alone is indicative of a positive test

• Negative: No turbidity and no color change after 72 hours of incubation.