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KMID : 1007520010100030323
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Food Science and Biotechnology
2001 Volume.10 No. 3 p.323 ~ p.326
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Suitability of Overlay method for Recovery of Heat - Injured Listeria monocytogenes and Salmonella typhimurium
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Lee Sun-Young
Kang Dong-Hyun
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Abstract
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This study was conducted to evaluate selective overlay medium method (OV) for selective enumeration of heat-injured Listeria monocytogenes and Salmonella typhimurium. Selective media such as Listeria Selective Agar (LSA) for L monocytogenes or Xylose Lysine Desoxycholate (XLD) for S. typhimurium contain agents that can inhibit injured target microorganisms. Non-selective media such as Tryptic Soy agar (TSA) can recover sub-lethally injured microorganisms, but do not have selectivity for isolation of specific foodborne pathogens. In the case of OV method, selective agar is added to the top of TSA resulting to contact selective agents to microorganisms directly. This phenomenon imparted selectivity and differentiation to the system. Listeria monocytogenes and S. typhimurium were injured by 62.8℃ and 55℃ heat, respectively, for 15 min in Butterfields phosphate buffer. After resuscitation of heat-injured foodborne pathogens on TSA for 2 hr at 37℃, 7 mL selective media (LSA for L. monocytogenes or XLD for S. typhimurium) were overlaid on the inoculated TSA, and the plates were further incubated at 37℃ for 22 hr. The injured pathogens were recovered on TSA, selective media, and OV The recoveries of heat-injured L. monocytogenes and S. typhimurium were not significantly different between TSA and OV (P>0.05). Therefore, OV was reliable for selectively recovering heat-injured L. monocytogenes and S. typhimurium.
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KEYWORD
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