Listeria monocytogenes Gram stain. Smear made from a liquid culture (tryptic soy broth, 48 hours, 37°C).

Small Gram-positive rods without chaining (palisade formation similar to diphtheroids).

L. monocytogenes is a Gram-positive bacterium, motile via peritrichous flagella at 30°C and below, but usually not at 37°C [2].
L. monocytogenes can move within eukaryotic cells by explosive polymerization of actin filaments (known as comet tails or actin rockets).