Listeria Spp

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Listeria is genus of gram positive rod shaped bacteria of which the specie, listeria monocytogenes causes listeriosis. There are six other non-pathogenic species – L grayi, L inocua, L ivanovii, L seeligeri and L welshimeri, which are non-pathogenic. Listeriosis is a disease that causes severe illness that has a mortality rate of 20%. Listeria monocytogenes is found in the gut of ruminants and can be divided into 16 serovars on the basis of somatic and flagellar antigens. It is a facultative anaerobic and a very hardy bacteria which can survive drying and freezing. Listeria monocytogenes expresses beta hemolysin which causes haemoglobin to rupture.

This bacteria is found commonly in uncooked meats and vegetables, in milk cold foods, ice creams and ready to eat meats like hot dogs. To prevent infection of ready to eat foods, factories that produce them are advised to continuously monitor the environment and production equipment for Listeria to prevent its establishment in the plant.

Arasains in Indonesia supplies Biolife culture media which can be used to cultivate and identify Listeria spp and L monocytogenes. Listeria monocytogenes grows on the Mueller Hinton agar. Identification is enhanced if the agar has sheep blood as a small zone of haemolysis can be seen around the colonies. Haemolysis differentiates Listeria from coryneform bacteria. The method of analysis requires 24-48 hours of pre enrichment followed by other tests. Biocontrol Indonesia supplies VIP Gold, a lateral flow device to detect all 6 species of listeria including L mono, thus providing a good indication of product and surface quality. This is a labour saving single step enrichment protocol for all sample types. The VIP Gold is an AOAC approved method. Biocontrol Indonesia also supply Transia plate for the detection of Listeria spp or only Listeria monocytogenes. This is a sandwich ELIZA technology that is used with a 96 well microtitre plate. For large volume testing the process can be automated using the Gemini Analyzer. This test has AFNOR and NORD Val approvals. For listeria spp there is only a single enrichment step whilst for L mono there is a first enrichment step in Demi Fraser broth of 20 hrs at 30°C and a second enrichment in Fraser broth for 24 hrs at 37°C. The time for ELIZA test is 2hr and 40 min. Biocontrol Indonesia provides a PCR platform, Assurance GDS, for detection of Listeria spp and L mono. This method has three levels for the isolation of bacteria. Enrichment is a single step with time to results in 24 hrs.