| 產品名稱： | 月桂基硫酸鹽胰蛋白胨肉湯；十二烷基硫酸鹽肉湯；LST培養基 |
|---|---|
| 英文名稱： | Lauryl Tryptose Broth；Lauryl Sulphate Broth；LST |
| 培養基類型： | 選擇性培養基 |
| 級別： | for microbiology |
| 品牌： | ELITE-MEDIA |
| 產品目錄號： | M244-01、M244-02 |
| 產品規格： | 250g、500g(添加劑需另購) |
| 產品外觀： | 淺黃色粉末。 |
| 顏色與澄清度： | 黃色透明溶液。 |
| 保存條件： | 密封，2-25度保存。 |
| 注意事項： | 避免呼入和皮膚接觸。 |
| 相關產品： | -- |
產品描述：
月桂基硫酸鹽胰蛋白示肉湯（Lauryl Tryptose Broth）簡稱LST培養基，是大腸菌選擇性液體培養基，用于檢測食品、水、奶制品中的大腸菌群和大腸埃希氏菌。本產品配方采用美國公眾健康協會APHA規定配方，用于檢測水和污水中的大腸菌群，同時也是《細菌學分析手冊》采用的配方。
用途：
APHA推薦十二烷基硫酸鹽胰蛋白示肉湯用于MPN計數法初步檢測水、工業廢水或污水中的大腸菌群，驗證其發酵乳糖產氣能力。該培養基也被APHA推薦檢測食品中的大腸菌群。
月桂基硫酸鹽胰蛋白示肉湯培養基用于檢測或確認產氣大腸桿菌（coli-aerogenes）的存在。
原理：
大腸菌群時革蘭氏陰性桿菌，能夠快速發酵乳糖產氣（水不溶性氣體）。更為準確的定義是35°C條件下能夠在LST培養基和BGLB培養基中生長，并且發酵乳糖產氣的革蘭氏陰性桿菌。在44.5°C條件下，還能夠在EC肉湯中發酵乳糖產氣的屬于大腸菌群的一個子集——糞大腸菌群。表面活性劑如膽鹽、蓖麻油酸鈉，一直以來作為抑制成分，用于配制選擇性培養基。十二烷基硫酸鈉（SDS）在大腸菌選擇性培養基中效果最好，完全阻止革蘭氏陽性菌生長。十二烷基硫酸鹽胰蛋白示肉湯可以在小量接種的情況下支持大腸菌的密集生長并產生大量氣體。該培養基另外一個優點是可用于直接檢測吲哚的存在。如果需要，可以在培養后加入指示劑。
向培養基中加入4-甲基傘型酮-β-D-葡糖苷酸（MUG）可以提高檢測大腸埃希氏菌的靈敏度。不產氣的大腸埃希菌菌株也能用MUG鑒別。MUG是一種生熒光化合物。大腸埃希氏菌具有合成Beta-葡萄糖苷酶的能力，水解MUG生成熒光化合物。在366nm波長的紫外燈下，培養基顯熒光，實現大腸埃希氏菌的快速檢測。
配方與配制方法：
| 成分 | g/L |
|---|---|
| 胰蛋白示 | 20.0 |
| 乳糖 | 5.0 |
| K2HPO4 | 2.75 |
| KH2PO4 | 2.75 |
| NaCl | 5.0 |
| 十二烷基硫酸鈉 | 0.1 |
| 終溶液pH | 6.8 ± 0.2 |
配制方法：
1. 稱取35.6g本品，加水1L去離子水溶解。
2. 分裝10ml培養基到20×150mm試管中，確保液面沒過倒置的10×75mm德拉姆發酵管。
3. 121°C高溫蒸汽滅菌15min。
實驗方法：
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.