Cultivate Listeria monocytogenes
Listeria is a genus of gram-positive, non-sporeforming, rod-shaped bacteria. Of the known Listeria species, Listeria monocytogenes requires particular attention as a human and animal pathogen;
L. ivanovii is only pathogenic in animals, while L. innocua, L. seeligeri, L. grayi, and L. welshimeri are considered harmless environmental bacteria.
Listeria are characterized by several properties, including their ability to grow at refrigeration temperatures (2–8°C). They are thus a potentially serious risk for ready-to-eat foods. Consequently, food legislation in many countries specifies strict limits for Listeria spp. or Listeria monocytogenes. In the conduct of risk-related quality controls in food, tests should be run for L. monocytogenes, and for Listeria in general. The presence of Listeria – in particular of L. innocua – is an indicator for critical hygienic conditions in the production process. A drastic increase in the incidence of food infection caused by Listeria has resulted in a demand for reliable methods of detection.
Merck’s dehydrated culture media for cultivating Listeria monocytogenes and Listeria spp. meet the stringent performance standards as set out in ISO 11133. Its unique granules cause far less dust than powdered media and ensure excellent solubility and homogeneity. The granules dissolve rapidly in water, and there is hardly any separation of components or clumping, even in warm, humid conditions. The outstanding properties of Merck dehydrated culture media make them very easy to use and highly efficient.
Listeria monocytogenes is one of the most widely distributed foodborne pathogens in the world and is responsible for severe infections in immunocompromised persons, pregnant women and neonates. As a result, the mortality rate in infected individuals is high despite the relatively low number of cases around the world. Listeria infections (listeriosis) can result in anything from mild gastroenteritis to severe cases of sepsis, meningitis, encephalitis or abortion. Due to the ubiquitous distribution of Listeria and their capability to grow at refrigeration temperatures (2–8°C), food products constitute one of the main sources of infection.
|Method||ISO 11290-1||FDA-BAM Chapter 10||FSIS MLG 8.07|
|Pre-enrichment||Half Fraser broth, 30±2°C, 24±3 h||bLEB base broth, 30°C, 4 h||UVM, 30±°2C, 22±2 h|
|Selective enrichment||Fraser broth, 35-37°C,
|bLEB w. selective agents added, 30°C, 20 h (44 h)||MOPS-bLEB, 35±2°C, 22±2 h or
Fraser Broth, 35±2°C,
24 h (48 h)
|Isolation||ALOA agar + additional, 24±3 h /
|Oxford, Palcam, Chromocult Listeria, 35°C,
24 – 48 h