Label MacConkey agar plates with dilution factor (100, 10-1, & 10-2). You will p
ID: 275855 • Letter: L
Question
Label MacConkey agar plates with dilution factor (100, 10-1, & 10-2). You will plate out each dilution and the undiluted sample in triplicate Tubes containing 4.5ml of diluent with the dilution factor: 10-1, & 10-2. Mix the water sample to ensure the cells are evenly dispersed. Aseptically transfer 0.5ml of water into the dilution blank labeled 10-1. This is a ten-fold dilution (1:10 or 10-1 dilution). Aseptically transfer 0.5ml of the 10-1 dilution into the dilution blank labeled 10-2. Using pipette transfer 0.1ml of the 10-2 dilution to the surface of an agar plate Repeat until you have inoculated 3 plates with this dilution. Now with the 10-1 dilution inoculate 3 more plates, and repeat with the undiluted sample (the 10-0 dilution).
1. Calculate the average number of colony-forming units (CFU)
2. Calculate the number of CFU/mL and determine the number of bacteria in the original sample
Dil. Plate 1 Plate 2 Plate 3 CFU/mL Average # of CFU 100 10-1 10-2 72 16 0 89 10Explanation / Answer
Answer:
1. Average CFU : 100 :247, 10-1:24, and 10-2 :0.6.
2. CFU/mL: 0.1mL* 1/10 = 24*100 = 2400;
similarly, 0.1mL * 1/100= 0.6 * 1000= 600
and in the original sample the number of bacteria were 247*10=2470.
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