Kang D H, Fung D Y
Department of Animal Sciences and Industry, Kansas State University, Manhattan 66506-1600, USA.
Int J Food Microbiol. 2000 Mar 10;54(1-2):127-32. doi: 10.1016/s0168-1605(99)00174-9.
Xylose lysine decarboxylase (XLD) medium, a selective plating medium, can inhibit heat-injured Salmonella typhimurium from growing, whereas tryptic soy agar (TSA), a nonselective medium, does not. To facilitate recovery of heat-injured S. typhimurium cells while providing selectivity of isolation of S. typhimurium from other bacteria in the sample, a thin agar layer (TAL) procedure was developed by overlaying 14 ml of nonselective medium (TSA) onto prepoured and solidified XLD medium in a 8.5 cm diameter Petri dish. During the first few hours of incubating the plate, the injured S. typhimurium repaired and started to grow in the TSA. During the resuscitation of injured cells, the selective agents from XLD were diffused to the TSA top layer part. Once the selective agents diffused to the top part of the TAL, the resuscitated S. typhimurium started to produce a typical reaction (black color) and other microorganisms were inhibited by the selective agents. The recovery rate for heat-injured (55 degrees C for 15 min) S. typhimurium with the TAL method was compared with TSA, XLD, and the traditional overlay method (OV; pouring selective agar on top of resuscitated cells on TSA agar 3-4 h after incubation). No significant difference occurred among TSA, OV, and TAL (P > 0.05) for enumeration of heat-injured S. typhimurium, but they recovered significantly higher numbers than from XLD agar (P < 0.05).
木糖赖氨酸脱羧酶（XLD）培养基是一种选择性平板培养基，能够抑制热损伤的鼠伤寒沙门氏菌生长，而胰蛋白胨大豆琼脂（TSA）这种非选择性培养基则不能。为了便于热损伤的鼠伤寒沙门氏菌细胞复苏，同时从样本中的其他细菌中选择性分离出鼠伤寒沙门氏菌，开发了一种薄琼脂层（TAL）方法，即将14毫升非选择性培养基（TSA）覆盖在直径8.5厘米的培养皿中预先倒入并凝固的XLD培养基上。在培养平板的最初几个小时内，受损伤的鼠伤寒沙门氏菌进行修复并开始在TSA中生长。在受损细胞复苏过程中，XLD中的选择剂扩散到TSA顶层部分。一旦选择剂扩散到TAL的顶层，复苏后的鼠伤寒沙门氏菌开始产生典型反应（黑色），其他微生物则被选择剂抑制。将TAL方法对热损伤（55摄氏度，15分钟）的鼠伤寒沙门氏菌的回收率与TSA、XLD以及传统覆盖法（OV；在孵育3 - 4小时后，将选择性琼脂倒在TSA琼脂上复苏的细胞上）进行比较。对于热损伤的鼠伤寒沙门氏菌计数，TSA、OV和TAL之间没有显著差异（P > 0.05），但它们回收的菌数明显高于XLD琼脂（P < 0.05）。
