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.



  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