Using saline tubes containing 9 ml of saline (for dilutions), draw a diagram that would yield between 30 and 300 colonies from an original broth culture that contains 5 * 10^8 cells/ml. Indicate volumes used and dilutions made for each tube and plate.

As shown in this diagram, you perform a ten-fold serial dilution of a culture to determine the number of colony forming units (CFU) per mL it contains.  You do a plate count with these growth results (no. of colonies for each dilution): 1:10 too many to count; 1:100 too many to count; 1:1,000 312; 1:10,000 38; 1:100,000 no growth.   The number of CFU per mL in the original culture was:   A. 38 B. 380,000  C. 38,000 D. None of the other four answers (Correct answer not given) E. 10,000

A sample is diluted by a factor of 10 five times. The 10^-3 dilution has 272 colonies on it. Assuming you plated the same volume on each plate, how many colonies would you expect to find on the 10^-4 plate? Include units and use OCD formula.

A culture of S. cerevisea has an overnight OD of 4.5 (1.0 OD is approx 1.0x107 cells/ml) You will be plating 100µl onto agar and want the final count of colonies on the plate to be around 300 colonies.  How much of the 4.5 OD culture must you use to get a 500µl subdilution (with sterile water), so that you have diluted enough to get approx 300 colonies per 100ul

Using your fingers, you are asked to aseptically touch the surface of a sterile agar plate. Illustrate the possible result from this step if your fingers are (a) unwashed – touched various things prior to placing on agar surface, and (b) washed with soap or disinfected with 70% alcohol. Describe the relative abundance of microbial growth observed on the plates.    List and draw the possible characteristics of an isolated bacterial colony that can be observed based on type of (a) margin, (b) elevation, (c) texture, and (d) optical property.

Why should agar media be completely dissolved before they are dispensed in tubes and plates? What are the bases for pegging the temperature at 1210C for 15-30 minutes during moist heat sterilization and 1800C for two (2) hours using dry heat sterilization? Can you sterilize culture media using dry heat sterilization? Why is that so? You will notice in the videos shown, the cotton plug is not used. What is role of cotton plug in media prep, sterilization and culture of microorganisms?       Instead of using cotton plug, plastic screw-cap is used, can you substitute this for the former? Is it technically acceptable in microbiology?

You have found that the D-value (decimal reduction value) of an antimicrobial agent to be 4 minutes when the agent was exposed to a bacterial culture having an initial total viable cel1 count of 10° CFU/mL. After 4 minutes upon addition of the antimicrobial agent, what would have been the total viable count of the culture in this experiment? A) O 10° CFU/mL B) O 10$ CFU/mL C) O 10° CFU/mL D) O 10' CFU/mL

A bacterial culture has a concentration of 3.2 x 108 cells /mL.  You dilute this culture as follows: 1/50, then 10-3and finally 1/20.  If you then plate 0.2 mL of the final dilution, how many CFU would you expect following incubation?