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Chapter 5

Culture Media and Methods for the Isolation of Listeria monocytogenes

The first isolation methods for the detection of Listeria spp. were based on the direct culture of samples on simple agar media, but isolation of the pathogenic Listeria monocytogenes was difficult. In time, new media were developed based on a variety of selective and elective agents in enrichment and isolation enumeration media. The recovery of low numbers of L. monocytogenes from foods and environmental samples requires the use of enrichment cultures followed by selective plating. In this chapter the development of selective media, including so-called differential media on which L. monocytogenes can be distinguished from other, non-pathogenic, species, are discussed. Little attention is paid to pre-enrichment media, recommended for the recovery of injured organisms, because in our opinion the presence of listeriae in products that receive a listericidal treatment is mainly due to post-process contamination. The introduction of chromogenic media, such as agar Listeria according to Ottoviani and Agosti (ALOA) allows the recovery of Listeria and L. monocytogenes from a variety of foods with relative ease.

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06 Dec 2011
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