Leucine Amino peptidase (LAP) Test: Principle, Procedure and results

Leucine Amino peptidase (LAP) Test is used to identify catalase negative gram-positive cocci.

The LAP disk is a rapid test for the detection of enzyme lucine amino peptidase.

Leucine-beta-naphthylamide impregnated disk serve as a substrate for the detection of lucine aminopeptidase. Following hydrolysis of the substrate by enzyme, the resulting beta- naphthylamineprodeces a red color upon the addition of cinnamaldehyde reagent.

 

Method

  1. Before incubation, slightly dampen the LAP disk with reagent grade water. Do not supersaturate the disk.
  2. Using a wooden applicator stick, rub a small amount of several colonies of an 18 to 24 hour pure culture onto a small area of the LAP disk.
  3. Incubate at room temperature for 5 minutes.
  4. After the incubation period, add 1 drop of cinnamaldehyde reagent.

 

Expected results

  1. Positive: Development of a red color within 1 minute after adding cinnamaldehyde reagent.
  2. Negative: No color change or development of a slight yellow color.

 

Quality control

  1. Positive: Enterococcus faecalis
  2. Negative: Leuconostoc spp
About tankeshwar 387 Articles
Hello, thank you for visiting my blog. I am Tankeshwar Acharya. Blogging is my passion, I am working as an Asst. Professor and Microbiologist at Department of Microbiology and Immunology, Patan Academy of Health Sciences, Nepal. If you want me to write about any posts that you found confusing/difficult, please mention in the comments below.

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