원유로부터 listeria monocytogenes의 분리방법에 대한 비교시험

Comparison of methods for isolation of listeria monocytogenes from raw milk

Methods used to isolate Listeria monocytogenes were compared in artificially contaminated raw milk. Three selective plating media, including Lithium chloride-phenylethanol-moxalactam(LPM) agar, Oxford agar(OxA), and Modified-McBride Listeria agar(MMA), were compared by using the media to direct plating method. The greatest numbers of positive Listeria samples were obtained on MMA of the used direct plating media, and MMA proved to be useful as a screening tool but was not very selective, beacause that was more distributed with various other microorganisms. Listeria colonies on OxA were very easy to identify on these agars due to the blackening of coloines. In a comparative study of FDA or USDA methods and both modified methods for the detection of L. monocytogenes from raw milk, both modified methods were modified by the inclusion of additional plating media and by the inoculum using centrifugal precipitation of 50ml milk samples. In ability to isolate L. monocytogenes by either the modified FDA and USDA methods, the modified FDA and USDA methods isolated more positive from the raw milk samples than the FDA or USDA methods. Comparison of modified FDA and modified USDA indicated that both were equally effective for the enumeration of the L. monocytogenes in raw milk samples. The higher numbers of non-Listeria microorganisms were obtained using FDA and USDA methods than modified methods. The number of other microorganisms isolated by four isolation methods were 4 to 6 kinds. The bacterial strains isolated by these methods were Acinetobacter spp., In general, Acinetobacter spp., Pseudomonas spp., Enterococcus spp. and Micrococcus spp. grew on LPM, while only Acinetobacter spp. grew on OxA. Therefore, OxA media was better than LPM in isolating L. monocytogenes.