Listeria are Gram-positive, motile (at mesophilic condition), psychrotrophic bacteria with six (6) known species – L. monocytogenes, L. innocua, L. seeligeri, L. welshimeri, L. ivanovii, and L. grayi. They are associated with clinical importance due to their virulence activity. But among the six species of Listeria, the most prevalent is L. monocytogenes causing listeriosis including sepsis, meningitis, encephalitis, corneal ulcer, pneumonia, cervical infection, and abortion, where elderly, immunocompromised, pregnant women and infants are the most susceptible. Due to the increasing Listeria outbreak, certain high-risk food became necessary to test for Listeria contamination. These high-risk foods are as follows: ready-to-eat seafood, pre-packed fruits and vegetables, drinks made from fresh fruit, deli meats without further cooking process, unpasteurized milk, soft-serve ice cream, soft cheeses, salad dressings, and raw vegetable garnishes.
Blue or light blue colonies of about 1-2 mm in diameter
Listeria spp. Forms light blue/blue colonies on the Compact Dry LS
- 35 or 37±2℃, 24±2 – 48±3 hours