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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 | 2) You will use the fresh cultures 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. | 3. Label a 13 X 100 ml capped tube pre-aliquoted with 2 mL of sterile water for each isolate. Use your flamed and cooled loop (or a sterile toothpick) to pick up a visible amount of growth from your freshly grown cultures. Vortex gently. Compare this tube to teh 0.5 McFarland Standard and aseptically add more culture or sterile water until the cloudiness (turbidity) matches, by eye, the "cloudiness" (turbidity) of the cells in the glass tube matches, by eye, the turbidity of the 0.5 Standard. <BR> | ||
4 | 4. Repeat for each of your isolates.<BR> | ||
The ending volume is irrelevant. Vortex to mix. <BR> | 5. The ending volume is irrelevant. Vortex to mix. <BR> | ||
6. You will use these tubes as a source of organism for both the antibiotics and interactions assays today. <BR> | |||
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[[Image:mcfarlandtable.jpg]]<BR> | [[Image:mcfarlandtable.jpg]]<BR> | ||
