Bacteria in solution are often counted by a method known as serial dilu tion plating. Petri dishes with a nutrient agar are inoculated with a measured amount of solution. After 3 days of growth, an individual bacterium will have grown into a small colony that can be seen with the naked eye. Count ing original bacteria in the inoculum is then done by counting the colonies on
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This will help to reduce the concentration of bacteria in the solution and make it easier to count individual colonies on the agar plates. Show more…
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You culture an inoculum of bacteria using the pour plate method and start by mixing 1 mL of the sample with 9 mL of sterile broth medium in a tube (tube 1). You then repeat this process to carry out serial 1/10 dilutions, each time mixing 1 ml of the diluted bacteria with 9 mL of medium (tubes 2, 3, 4, 5). You prepare pour plates by mixing 1.0 mL from each tube with 15 mL of cooled but still melted agar poured into a petri dish, and allow to solidify. You then incubate the plates for 24 hours and count the resulting colonies on each plate. If you obtain 70 colonies on plate 2 (prepared using the 2nd tube), how many bacteria were present in your original sample?
Sri K.
You have a bacterial culture that you know has 600,000 bacteria/ ml. You do a 10 -fold serial dilution to achieve a 1/10,000 dilution and then plate 0.1ml of each of these dilutions. How many colonies do you expect to see at each dilution? You do serial dilutions on a water sample and plate the dilutions on agar plates. You count the colonies on each of the plates as follows. Assume you plated 0.1 ml per sample. Dilution Number of CFUs 1/100 TNTC 1/1,000 TNTC 1/10,000 190 1/100,000 23 1/1,000,000 2 Base on these results, what is your estimate for the total number of CFUs/ ml in the original sample?
Farhan A.
You want to estimate the number of phages that you have in a solution. You perform three 1 to 1000 dilution from the initial stock followed by three 1 to 2 dilutions. After all these dilutions you plates 100 ul of the final dilution on an agar plate with bacteria seeded on it. After 24 hours you count 23 round cleared areas on the plates (the rest of the plate is filled with bacteria). What are those cleared areas? And how many phages did you have in the initial solution? (4 points)
Madhur L.
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