Harlequin Listeria Chromogenic Agar

Harlequin® Listeria Chromogenic Agar was developed to isolate and differentiate L. monocytogenes and other Listeria spp. Listeria spp. are differentiated based on β-glucosidase enzyme activity and L. monocytogenes is differentiated based on its phospholipase enzyme activity. Lithium chloride in the base medium and supplementary antimicrobial compounds Ceftazidime, Polymyxin, Nalidixic acid and Cycloheximide provide the medium’s selectivity.


  1. Weigh 70.5 grams of powder and disperse in 950 mL of deionized water.
  2. Allow to soak for 10 minutes, swirl to mix
  3. Autoclave for 15 minutes at 121°C.
  4. Cool to 48-50°C and add 2 vials of reconstituted X072 supplement. Swirl to mix.
  5. Add 2 vials of X010 supplement (preheated to 48-50°C). Mix well with gentle end-over-end mixing and dispense into Petri dishes.
Typical Formulation g/Liter
Meat peptone 18 g
Tryptone 6 g
Yeast extract 10 g
Lithium chloride 10 g
Sodium chloride 5 g
Disodium hydrogen orthophosphate anhydrous 2.5 g
Sodium pyruvate 2 g
Glucose 2 g
Glycerophosphate 1 g
Magnesium solphate 0.5 g
5-bromo-4-chloro-3-indolyl-β-D-glucopyranoside 0.05 g
Agar 13.5 g
Grams per liter 70.5 g

Final pH: 7.2 ± 0.2