Cetrimide Agar

Question 1

Purpose of cetrimide agar:

Answer 1

This test t is primarily used to isolate and purify Pseudomonas aeruginosa from contaminated specimens.

Question 2

Principle of cetrimide agar:

Answer 2

this test is used to determine the ability of an organism to grow in the presence of cetrimide, a toxic substance that inhibits the growth of many bacteria by causing the release of nitro- gen and phosphorous, which slows or kills the organism.P. aeruginosa is resistant to cetrimide.

Question 3

Media of cetrimide agar:

Answer 3

Enzymatic digest of gelatin (20 g).
MgCl2 (1.4 g),
K2SO4 (10 gì,
cetrimide (cetyl- trimethylammonium bromide) (0.3 g),
agar (13.6),
pH 7.2.

Question 4

Method of cetrimide agar:

Answer 4

1. Inoculate a cetrimide agar slant with 1 drop of an 18- to 24-hour brain-heart infusion broth culture.
   3-Incubate at 35°-37°C for up to 7 days.. 3. Examine the slant for bacterial growth.

Question 5

Expected results of cetrimide agar:

Answer 5

Positive: Growth, variation in color of colonies
Negative: No growth

Question 6

Limitation of cetrimide agar:

Answer 6

Some enteric organisms will grow and exhibit a weak yellow color in the media. This color change is distinguishable from the production of fluorescein.

Additional testing is necessary to confirm a diagnosis of P. aeruginosa

Question 7

Quality control of cetrimide agar:

Answer 7

Positive: Pseudomonas aeruginosa -growth and color change; yellow-green to blue-green colonies
Negative: Escherichia coli -no growth and no color change