Question

One group want culture the Listeria innocua， what medium can be used？ please give your ansower and why?

Answer 1

Pure cultures of Listeria can be grown on different bacteriological media such as tryptose agar, nutrient agar and blood agar. Listeria utilize glucose for their growth and prefer aerobic conditions. They grow in temperature range of 0 to 45°C, pH range of 5.6 to 9.6 and water activity range of 0.9 to > 0.97. On a clear nutrient media, they appear sparkling blue green which makes them easy to be distinguished from other microroganisms.

Foods contain relatively low amounts of these organisms, making their isolation difficult. Therefore, a cold enrichment broth was used at 4°C to increase the number of listeria before their isolation on solid media. Certain selective agents can be added to the media which inhibit background organisms.

Examples : Lithium chloride – promotes growth of listeria and slows down growth of gram negative bacteria; nalidixic acid – inhibits growth of gram negative bacteria ; Moxalactam – inhibits mny gram positive and negative bacteria.