Lab土壤中細(xì)菌總數(shù)的測定

1、實(shí)驗(yàn)三 土壤中細(xì)菌總數(shù)的測定 一 教學(xué)要求 通過土壤中細(xì)菌總數(shù)的測定，了解微生物數(shù)量的測定方法，掌握平板菌落計(jì)數(shù)的原理和方法二 實(shí)驗(yàn)原理1、測定微生物生長的方法 Direct methods Direct counting，Coulter counter Indirect methods Viable Cell methods，Membrane filtration ， turbidity methods，most probable number(MPN) ,Detect chemical products or metabolic activity Alternative methods f

2、or viable cell counts2、The plate count (viable count) The number of bacteria in a given sample is usually too great to be counted directly. However, if the sample is serially diluted and then plated out on an agar surface in such a manner that single isolated bacteria form visible isolated colonies,

3、 the number of colonies can be used as a measure of the number of viable (living) cells in that known dilution. Colony-Forming Units (CFUs) However, keep in mind that if the organism normally forms multiple cell arrangements, such as chains, the colony-forming unit may consist of a chain of bacteria

4、 rather than a single bacterium. In addition, some of the bacteria may be clumped together. Therefore, when doing the plate count technique, we generally say we are determining the number of Colony-Forming Units (CFUs) in that known dilution. By extrapolation, this number can in turn be used to calc

5、ulate the number of CFUs in the original sample. calculate the number of CFUs in the original samplenumber of CFUs per ml of sample = number of colonies (30-300 plate) X the dilution factor of the plate countedFor a more accurate count it is advisable to plate each dilution in duplicate or triplicate and then find an average count. 三 材料與器材 無菌培養(yǎng)皿12套、1 mL無菌移液管10 支、土壤樣品、天平等。四 操作步驟 無菌平皿編號制備土壤稀釋液 傾注平板 培養(yǎng)(48h) 計(jì)數(shù) 五 注意事項(xiàng) 倒平板時要注意控制培養(yǎng)基的溫度。 稀釋操作時，要盡量減少樣品稀釋誤差，而且每個稀釋度的菌液應(yīng)各用一支無