Oxoid™ Palcam Agar Base 500g Each

Listeria monocytogenes from food samples. Its formulation incorporates a dual indicator system that enables clear differentiation of L. monocytogenes based on aesculin hydrolysis, mannitol non-fermentation, and resulting pH changes.

About Listeria monocytogenes
Listeria monocytogenes is the most frequently encountered pathogenic species within the Listeria genus, known to cause illness in both humans and animals. The PALCAM medium is based on the formulation by Van Netten et al.¹, and is widely recommended for isolating this pathogen from various food matrices.

Key Features
Highly selective: The inclusion of lithium chloride, ceftazidime, polymyxin B, and acriflavine hydrochloride suppresses competing microbial flora, enhancing recovery of Listeria monocytogenes.

Differential identification:

L. monocytogenes colonies appear brown to black with a black halo due to aesculin hydrolysis in the presence of ferrous iron.

Competing organisms like enterococci and staphylococci, which ferment mannitol, form yellow colonies as the phenol red pH indicator shifts from red to yellow.

Indicator System
Aesculin + Ferrous Iron: Detects aesculin hydrolysis (black halo)

Mannitol + Phenol Red: Detects mannitol fermentation (color change to yellow)

This dual indicator approach ensures accurate differentiation between Listeria monocytogenes and background flora.