45 Lab-3土壤中细菌总数的测定.ppt

第1页：实验三土壤中细菌总数的测定一教学要求通过土壤中

• 实验三土壤中细菌总数的测定一教学要求通过土壤中细菌总数的测定，了解微生物数量的测定方法，掌握平板菌落计数的原理和方法二实验原理1、测定微生物生长的方法
• Direct methodsDirect counting，Coulter counter
• Indirect methodsViable Cell methods，Membrane filtration，turbiditymethods，most probable number(MPN) ,Detect chemicalproducts or metabolic activity
• Alternative methods for viable cell counts

第2页：

第3页：

第4页：

第5页：2、Theplatecount

• 2、The plate count (viable count)
• The number of bacteria in a givensample is usually too great to becounted directly. However, if the sampleis serially diluted and then plated out onan agar surface in such a manner thatsingle isolated bacteria form visibleisolated colonies, the number ofcolonies can be used as a measure ofthe number of viable (living) cells in thatknown dilution.

第6页：Colony-FormingUnits

Colony-FormingUnits(CFUs)However, keep in mind that if the organism normallyforms multiple cell arrangements, such as chains, thecolony-forming unit may consist of a chain of bacteriarather than a single bacterium. In addition, some of thebacteria may be clumped together. Therefore, whendoing the plate count technique, we generally say weare determining the number ofColony-Forming Units(CFUs)in that known dilution. By extrapolation, thisnumber can in turn be used to calculate the number ofCFUs in the original sample.

第7页：calculatethenumberof

calculatethenumberofCFUsintheoriginalsamplenumber of CFUs per ml of sample =number of colonies (30-300 plate) X the dilutionfactor of the plate countedFor a more accurate count it is advisable to plateeach dilution in duplicate or triplicate and thenfind an average count.

第8页：三材料与器材

• 三材料与器材
• 无菌培养皿12套、1 mL无菌移液管10支、土壤样品、天平等。

第9页：四操作步骤无菌平皿编号→制备土壤稀释液→

四操作步骤无菌平皿编号→制备土壤稀释液→倾注平板→培养(48h)→计数

第10页：五注意事项

• 五注意事项
• 倒平板时要注意控制培养基的温度。
• 稀释操作时，要尽量减少样品稀释误差，而且每个稀释度的菌液应各用一支无菌吸管。
• 为使菌落能在平板上均匀分布，样品液加入平皿后，应尽快倾注培养基并旋转混匀。六思考题
• 要测定某种液体饮料中的活细菌总数，除了采用平板菌落计数法外，还可采用哪些方法？