1. You are given a milk sample that Mr. Milkman claims contains 4.5 x 108 CFU/ml. He claims this is within the limit of acceptable CFU/ml for Grade A milk. Diagram a procedure he could use to determine the CFU/ml and information pertinent to proving or disproving Mr. Milkman's claim. Is the milk within the acceptable limit?
2. A plate of nutrient agar, labeled 10-4, has 255 colonies on it and another plate of media, labeled 10-5, has 27 colonies on it. What would be the number of CFU/ml in the original sample?
3. I give you 6 mls of an overnight culture of Micrococcus luteus at a concentration of 4.5 x 106 CFU/ml. Diagram a dilution series to obtain countable plates by using tubes containing 9 ml nutrient broth (NB) and fixed-volume 1ml pipettes (won't measure any more or less than 1ml).
4. I give you a very expensive strain of E. coli containing 106 CFU/ml and tell you that I need exactly 10ml of the same E. coli culture at a concentration of 103 CFU/ml (I don't want any excess culture). Using a dilution series, how would you get the correct concentration and volume of bacteria? Make this a realistic scenario.
5. You are working at the local health department as a microbiologist. A number of people attest that chicken they bought at Mytummyhurts Grocery smells rotten. You take 50 gm (this is equal to ~ 55 ml) of the chicken, place it in a volume of 450 ml dH2O, and liquefy it. What is the dilution in simplest terms?
6. If you had a liquid culture of Staphylococcus aureus and transferred 2 ml to test tube "R", which contains 6 ml of nutrient broth, what would be the final dilution (in simplest terms) of the culture in test tube "R"? From the culture in "R" make a 1:8 dilution in tube "S" (this is not the final or overall dilution). Now, determine what is the final or overall dilution of the culture in tube "S"?
7. Perform a 2-fold serial dilution using 4 tubes containing 1 ml of NB each and a 12 ml broth culture of Bacillus subtilis; use the same B. subtilis culture and perform a 2-fold serial dilution using 4 tubes containing 2 ml of NB each; repeat in a similar fashion using 4 tubes containing 0.5 ml each.
8. I have 400 mls of an antibiotic stock solution at a concentration of 16 mg/ml. I would like a final volume of 8 mls of the antibiotic at a concentration of 4.2 mg/ml. How much of the stock solution do I need to obtain this?
9. How would you prepare 21 ml of a 1:7 dilution?
10. How would you prepare 16 ml of a 1: