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  • 大腸菌群和大腸桿菌菌落計數方法

    發布時間:

    2022-12-24

    作者:

    購買培養基買哪家公司


     1.平板計數法

    通常使用的培養基為紫紅膽鹽乳糖瓊脂。準備兩套平板,每個平板各加入稀釋范圍內的樣品液1ml,另加15ml熔化并冷卻至45℃的紫紅膽鹽乳糖瓊脂充分混勻。再覆蓋5ml瓊脂培養基,凝固后將平板翻轉,置于35℃培養24h,進行大腸菌群計數。培養后的大腸菌群為深紅色菌落。通常典塑大腸菌群的菌落直徑為0.5mm或稍大,緊貼菌落周圍有膽鹽沉淀。當幾個菌落長在一起時菌落可能變小。如果食品中含有碳水化合物而不含乳糖,那么當低稀釋度(既高濃度)食品加到培養基中可能導致前文提及的異常結果。對10-2或更低稀釋度的平板,有必要對大腸菌群的假陽性結果進行驗證,可將菌落挑選出來,轉接到乳糖肉湯或麥康凱肉湯中在35℃培養后驗證,或用Eijk-man試驗驗證大腸桿菌的存在。
    2.干燥復水膜計數法

    干燥復水膜是一種十分有用的大腸桿菌計數膜。用紫紅膽鹽培養基作為基礎培養基,添加5-溴-4-氯-吲哚-β-葡萄糖苷酸以檢測葡萄糖醛酸的活性。大腸桿菌在平板上為藍色菌落并伴有氣泡產生。該產品便于操作和讀數,巳被作為AOAC確認為官方方法。
    3.濾膜法

    將濾膜(MF)和改進的選擇性培養基結合使用,可檢測某些樣品中的大腸菌群和大腸桿菌。該方法對飲用水的檢測十分有用。


    1. Plate counting method
     
    The medium commonly used is agar-agar, a purple gallate lactose. Prepare two sets of tablet, within the scope of each tablet to dilute liquid samples 1 ml, plus 15 ml of melting and cooling to 45 ℃ amaranthine lactose bile salt AGAR thoroughly incorporated. Covering 5 ml AGAR medium, will turn tablet after solidification, under 35 ℃ for 24 h, fecal coliform count. The cultured coliform colonies were dark red colonies. Usually, the diameter of the colony of coliform coliform coliforms is 0.5mm or slightly larger. Colonies may become smaller when several colonies grow together. If a food contains carbohydrates without lactose, the addition of a low-dilution (i.e., high concentration) food to the culture medium may result in the abnormal results mentioned above. For 10-2 or lower dilution degrees of tablets, it is necessary to verify the false positive results of fecal coliform, colony can be selected, through to lactose broth or macconkey broth cultured in 35 ℃ after verification, or use the Eijk - man test verifies the existence of e. coli.
    2. Dry rehydration membrane counting method
     
    Dry rehydration membrane is a very useful escherichia coli counter membrane. The activity of glutaric acid was detected by adding 5-bromo-4-chloro-indole - glycosidic acid as the basic culture medium. E. coli is a blue colony on the plate with bubbles forming. The product is easy to operate and read and has been recognized as an official method by AOAC.
    3. The membrane filter technique
     
    The colonic flora and e. coli in some samples can be detected by the combination of the filter membrane (MF) and the improved selective medium. This method is very useful for testing drinking water.
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