Which of the following plates (dilution factor) would you count/use to determine the original bacterial count? 1 ml Original inoculum Dilutions Plating 1:10 9 ml broth in each tube 1:10 1 ml 1 ml 1:100 1 ml 1:100 2 (1:100) 3 (1:1000) 4 (1:10,000) 5 (1:100,000) 1 ml 1:1000 1 ml 1 ml 1:1000 1:10,000 1 ml 1 ml 1:10,000 1:100,000 1 ml 1:100,000 Calculation: Number of colonies on platex reciprocal of dilution of sample= number of bacteria/ml (For example, if 32 colonies are on a plate of ¹/10,000 dilution, then the count is 32 x 10,000 = 320,000/ml in sample.) Copyright ©2004 Pearson Education, Inc., publishing as Benjamin Cummings

Why is aseptic urine collection important when cultures are ordered? If you counted 20 colonies from a 0.01-ml inoculum of a 1:10 dilution of urine, how many organisms per milliliter of specimen would you report? Is this number significant? What can you learn from visual inspection of a urine specimen? How would you relate these to the microorganisms present in the sample? How are UTIs acquired/transmitted? Explain why E. coli is frequently implicated in cystitis in females.

A culture of Staphylococcus of unknown density is diluted as follows (letters represent each step): • 60 mL of a bacterial culture is diluted by adding 440 mL of water • 1000 microliters from (A) is added to 9 mL of water • Dilution (B) is used to prepare a 103 dilution in water • 100 ul from dilution (C) is plated to nutrient agar and incubated at 37°C Following incubation, colonies are uniformly distributed on the agar, and 102 colonies are counted on one half of the plate. 1. Express the total CFU/mL of the original culture in scientific notation. 2. If 10 ul is plated from dilution (C), how many colonies should grow on the plate? Edit View Insert Format Tools Table

A microbiologist sets up a serial dilution to analyze bacteria in raw milk.   Tube 1 – 0.1 mL milk diluted in 9.9 mL sterile water Tube 2 – 0.1 mL milk from Tube 1 diluted in 9.9 mL sterile water Tube 3 – 1.0 mL milk from Tube 2 diluted in 9.0 mL sterile water   What is the dilution of raw milk in Tube 3?

Abigail did not dry the top of her agar plate and stored it top up. Now she wants to count colonies but there is a smear over the entire plate. She was working with E. coli. Why does she have a smear?

Calculate the concentration of bacteriophage in the original culture from the following data. Be sure to include units. Show dilution factors for each test tube. Show the final dilution factor for test tube number 4. Show all your math. 0.1 ml 0.01 ml 0.001 ml 0.1 ml 1.0 ml plated 9.9 ml 9.99 ml 9.999 mi 9.9 m plaques Original Culture Test Test Test Test Tube #1 Tube #2 Tube #3 Tube #4 Dilution Factor: Concentration of Phage: