| 产品名称： | 月桂基硫酸盐胰蛋白胨肉汤；十二烷基硫酸盐肉汤；LST培养基 |
|---|---|
| 英文名称： | Lauryl Tryptose Broth；Lauryl Sulphate Broth；LST |
| 培养基类型： | 选择性培养基 |
| 级别： | for microbiology |
| 品牌： | ELITE-MEDIA |
| 产品目录号： | M244-01、M244-02 |
| 产品规格： | 250g、500g(添加剂需另购) |
| 产品外观： | 浅黄色粉末。 |
| 颜色与澄清度： | 黄色透明溶液。 |
| 保存条件： | 密封，2-25度保存。 |
| 注意事项： | 避免呼入和皮肤接触。 |
| 相关产品： | -- |
产品描述：
月桂基硫酸盐胰蛋白示肉汤（Lauryl Tryptose Broth）简称LST培养基，是大肠菌选择性液体培养基，用于检测食品、水、奶制品中的大肠菌群和大肠埃希氏菌。本产品配方采用美国公众健康协会APHA规定配方，用于检测水和污水中的大肠菌群，同时也是《细菌学分析手册》采用的配方。
用途：
APHA推荐十二烷基硫酸盐胰蛋白示肉汤用于MPN计数法初步检测水、工业废水或污水中的大肠菌群，验证其发酵乳糖产气能力。该培养基也被APHA推荐检测食品中的大肠菌群。
月桂基硫酸盐胰蛋白示肉汤培养基用于检测或确认产气大肠杆菌（coli-aerogenes）的存在。
原理：
大肠菌群时革兰氏阴性杆菌，能够快速发酵乳糖产气（水不溶性气体）。更为准确的定义是35°C条件下能够在LST培养基和BGLB培养基中生长，并且发酵乳糖产气的革兰氏阴性杆菌。在44.5°C条件下，还能够在EC肉汤中发酵乳糖产气的属于大肠菌群的一个子集——粪大肠菌群。表面活性剂如胆盐、蓖麻油酸钠，一直以来作为抑制成分，用于配制选择性培养基。十二烷基硫酸钠（SDS）在大肠菌选择性培养基中效果最好，完全阻止革兰氏阳性菌生长。十二烷基硫酸盐胰蛋白示肉汤可以在小量接种的情况下支持大肠菌的密集生长并产生大量气体。该培养基另外一个优点是可用于直接检测吲哚的存在。如果需要，可以在培养后加入指示剂。
向培养基中加入4-甲基伞型酮-β-D-葡糖苷酸（MUG）可以提高检测大肠埃希氏菌的灵敏度。不产气的大肠埃希菌菌株也能用MUG鉴别。MUG是一种生荧光化合物。大肠埃希氏菌具有合成Beta-葡萄糖苷酶的能力，水解MUG生成荧光化合物。在366nm波长的紫外灯下，培养基显荧光，实现大肠埃希氏菌的快速检测。
配方与配制方法：
| 成分 | g/L |
|---|---|
| 胰蛋白示 | 20.0 |
| 乳糖 | 5.0 |
| K2HPO4 | 2.75 |
| KH2PO4 | 2.75 |
| NaCl | 5.0 |
| 十二烷基硫酸钠 | 0.1 |
| 终溶液pH | 6.8 ± 0.2 |
配制方法：
1. 称取35.6g本品，加水1L去离子水溶解。
2. 分装10ml培养基到20×150mm试管中，确保液面没过倒置的10×75mm德拉姆发酵管。
3. 121°C高温蒸汽灭菌15min。
实验方法：
Lauryl Tryptose Broth is recommended for the detection and enumeration of coliform organisms in water and milk products, especially in the control of ice-cream manufacture and in dairy hygiene. A suggested procedure ( Dyett7 ) is as follows:1.Inoculate samples of ice cream into tubes of Lauryl Tryptose Broth in the manner normally employed in the MacConkey test. Examine the tubes after overnight incubation at 35°C and, if no gas is visible, examine again at the end of 48 hours’ incubation.
2.From every tube showing fermentation (primary fermentation), two further tubes of Lauryl Tryptose Broth are inoculated, and these are incubated at 35°C and 44°C respectively. It is advisable that the tube to be incubated at 44°C be warmed in a water bath at this temperature before inoculation.
3.After the two tubes of Lauryl Tryptose Broth have been inoculated for secondary fermentation, test the original primary fermentation tube (which was inoculated directly with ice cream) for indole production. A positive reaction suggests the presence of Escherichia coli and confirmation will be obtained later with the secondary fermentation from the 44°C bath. A negative indole reaction in the primary fermentation tube indicates the absence of E. coli.
4.Check the 44°C incubated secondary broth for fermentation after seven hours. If positive, test for indole production with either Ehrlich or Kovac’s reagent. Due to the lauryl sulphate present, shaking the reagent culture mixture forms a persistent emulsion which interferes with the test. This may be avoided by shaking with ether, which separates rapidly, and then adding Kovac’s reagent to the layer without shaking.
5.If fermentation has not occurred after seven hours, leave the tube overnight at 44°C and test the following day. A positive indole reaction in a broth that has produced gas at 44°C indicates the presence of E. coli.
6.The tube at 35°C is incubated for 24 hours. If no fermentation occurs, the primary fermentation is assumed to be due to organisms other than coliforms. False positives are not uncommon in the primary fermentation tubes, due to fermentation of the sucrose in the added ice cream by organisms other than coliforms.
