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BISC209/F13: Lab7: Difference between revisions
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→McFarland Turbidity Standards
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1) Although cell density can be measured more accurately using a spectrophotometer to measure optical density (OD) at 600nm, we will use a quicker method that will work well enough for our purposes. We will use a McFarland 0.5 standard; the 0.5 refers to the approximate concentration of organisms in solutions which is 1.5X10<sup>8</sup> cfu/mL for the 0.5 standard. Other common standards are shown in the table below. <BR> | 1) Although cell density can be measured more accurately using a spectrophotometer to measure optical density (OD) at 600nm, we will use a quicker method that will work well enough for our purposes. We will use a McFarland 0.5 standard; the 0.5 refers to the approximate concentration of organisms in solutions which is 1.5X10<sup>8</sup> cfu/mL for the 0.5 standard. Other common standards are shown in the table below. <BR> | ||
2) You will use the fresh broth culture of each of your isolates that you prepared prior to lab for both the antibiotic and interactions protocols. We want to apply relatively the same number of organisms in each procedure so we will use McFarland Standard | 2) You will use the fresh broth culture of each of your isolates that you prepared prior to lab for both the antibiotic and interactions protocols. We want to apply relatively the same number of organisms in each procedure so we will use McFarland Standard to "correct" turbidity. <BR> | ||
3. If your fresh broth is more turbid than the McFarland Standard, pipet one ml of the broth culture into a sterile glass tube and adjust the concentration of the cells by matching by eye the "cloudiness" (turbidity) of the cells in the glass tube to a standard provided by your instructor. <BR> | 3. If your fresh broth is more turbid than the McFarland Standard, pipet one ml of the broth culture into a sterile glass tube and adjust the concentration of the cells by matching by eye the "cloudiness" (turbidity) of the cells in the glass tube to a standard provided by your instructor. <BR> | ||
