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This Concept Map, created with IHMC CmapTools, has information related to: LAB 4 - ENUMERATION OF MICROORGANISMS, plate count (viable count) tools used 1.0 milliliter pipette and filler, plate count (viable count) tools used turntable and bent glass rod, Turbidimetric measurement can be correlated with some other method of cell count, such as the direct microscopic method or the plate count. In this way, turbidity can be used as an indirect measurement of the cell count. procedure 1. Several dilutions are made of a bacterial stock. 2. A Petroff-Hausser counter is used to perform a direct microscopic count on each dilution. 3. A spectrophotometer is then used to measure the absorbance of each dilution tube. 4. A standard curve comparing absorbance to the number of bacteria can be made by plotting absorbance versus the number of bacteria per cc. 5. Once the standard curve is completed, any dilution tube of that organism can be placed in a spectrophotometer and its absorbance read. Once the absorbance is determined, the standard curve can be used to determine the corresponding number of bacteria per cc., Enumeration of Microorganisms method direct microscopic count (total count), When bacteria are suspended in a liquid medium, the culture appears turbid. This is because bacterial culture acts as a colloidal suspension that blocks and reflects light passing through the culture. Within limits, the light absorbed by the bacterial suspension will be directly proportional to the concentration of cells in the culture. measuring turbidity The instrument used to measure turbidity is a spectrophotometer., percent light transmitted description The percent of light transmitted is inversely proportional to the bacterial concentration. (The greater the percent transmittance, the lower the number of bacteria.), A counting chamber consisting of a ruled slide and a coverslip is employed. The number of bacteria in a small known volume is directly counted microscopically and the number of bacteria in the larger original sample is determined by extrapolation. formula formula used: The number of bacteria per cc = The average number of bacteria per large double-lined square X The dilution factor of the large square (1,250,000) X The dilution factor of any dilutions made prior to placing the sample in the counting chamber, e.g., mixing the bacteria with dye, plate count (viable count) description The sample is serially diluted and then plated out on an agar surface in such a manner that single isolated colonies form. The number of colonies on a plate having between 30 and 300 colonies is then counted to determine the number of colony-forming units (CFUs) per milliliter., Enumeration of Microorganisms method plate count (viable count), direct microscopic count (total count) description A counting chamber consisting of a ruled slide and a coverslip is employed. The number of bacteria in a small known volume is directly counted microscopically and the number of bacteria in the larger original sample is determined by extrapolation., The instrument used to measure turbidity is a spectrophotometer. also, Turbidimetric measurement can be correlated with some other method of cell count, such as the direct microscopic method or the plate count. In this way, turbidity can be used as an indirect measurement of the cell count., absorbance description The absorbance is directly proportional to the cell concentration. (The greater the absorbance, the greater the number of bacteria.), The instrument used to measure turbidity is a spectrophotometer. can measure absorbance, The sample is serially diluted and then plated out on an agar surface in such a manner that single isolated colonies form. The number of colonies on a plate having between 30 and 300 colonies is then counted to determine the number of colony-forming units (CFUs) per milliliter. formula formula used: The number of CFUs per ml of sample = The number of colonies (30-300 plate) X The dilution factor of the plate counted, turbidity description When bacteria are suspended in a liquid medium, the culture appears turbid. This is because bacterial culture acts as a colloidal suspension that blocks and reflects light passing through the culture. Within limits, the light absorbed by the bacterial suspension will be directly proportional to the concentration of cells in the culture., plate count (viable count) tools used vortex mixer, The instrument used to measure turbidity is a spectrophotometer. can measure percent light transmitted, Enumeration of Microorganisms method turbidity
