2. A series of 1 ml samples from tube #4 of the dilution s eries below are spread on agar plates, resulting in the growth of an average of 68 colonies per plate. What is the concentration of colony-forming units (cfu/mi) present in the original culture? 0.1 ml 0.1 ml 1 ml 1 ml 100 ml 9.9 ml 9.9 ml 9 ml 9 ml 2 4 3. The culture flask at left contains a total of 3.2 x 10s cfu. How man total cfu's are present in dilution tube #52 If you were to plate a 0.2 ml (200 μ) sample from tube #4, how many colonies would you expect to grow? 1 ml 0.1 ml I ml 1 ml 1 ml 200 ml 9 ml 9.9 ml 1 ml 1 ml 1 ml 4 2. A series of 1 ml samples from tube #4 of the dilution s eries below are spread on agar plates, resulting in the growth of an average of 68 colonies per plate. What is the concentration of colony-forming units (cfu/mi) present in the original culture? 0.1 ml 0.1 ml 1 ml 1 ml 100 ml 9.9 ml 9.9 ml 9 ml 9 ml 2 4 3. The culture flask at left contains a total of 3.2 x 10s cfu. How man total cfu's are present in dilution tube #52 If you were to plate a 0.2 ml (200 μ) sample from tube #4, how many colonies would you expect to grow? 1 ml 0.1 ml I ml 1 ml 1 ml 200 ml 9 ml 9.9 ml 1 ml 1 ml 1 ml 4
2- CFU/ml = number of colonies/ dilution factor * volume plated in ml. Dilution factor = 10-2*10-2*10-1*10-1 = 10-6. Volume Plated - 1ml. The number of colonies = 68. So CFU/ml in original culture = 68 / 10-6 = 68*106 6. 8 *107 CFU/ml 3- - CFU/ml = number of colonies/ dilution factor * volume plated in ml. Dilution factor = 10-1*10-2*10-1*10-1 *10-1 = 10-6. Volume Plated - 1ml. So CFU/ml in original culture = 3. 2* 108 3. 2* 108 = Number of colonies / 10-6 * 1 Number of colonies = 3. 2* 108 * 10-6 = 3. 2* 100 or 320 colonies. So we will get 320 colonies from the fifth tube when we plate 1ml of culture. Dilution for the fourth tube is 10-1*10-2*10-1*10-1= 10-5. Volume Plated = 0.2ml. 3. 2* 108 = Number of colonies / 10-5 * 0. 2 Number of colonies = 3. 2* 108 * 10-5 * 0. 2 = 3. 2*103 * 0. 2 = 3200 * 0. 2 = 640 colonies.
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