Activity 1 Teaching Strategies

Activity 1 - Instructor Teaching Strategies

TESTING PHIX174 HOST RANGE

SUGGESTED TEACHING STRATEGIES

Level of Difficulty: Beginner
Students will need a printed copy of the procedure.
Inexperienced students should first practice aseptic techniques on empty tubes before attempting the procedure. For streaming video tips on aseptic transfers, visit www.virology.net/Video.html, then click on "Microbiology laboratory procedures video", and "aseptic techniques."
Make sure students understand the solution in tube B is a1:10 dilution of the bacteriophage stock in tube A, while tube C represents a 1:100 dilution.
For an added challenge, students can calculate the titer of the Phi X 174 stock solution by counting the number of plaques on a plate (ideally, they should use the E. coli strain C plate that falls in the 30 to 300 plaques range). The titer of the stock solution will be equal to:

PFU / ml of stock solution = Plaque Forming Units / ml of stock solution = (the number of plaques on the plate) (fold dilution) / (0.2 ml)

For example, if a 0.2 ml of 10-fold dilution of the stock solution resulted in 50 plaques on the plate, the stock solution titer would be equal to: (50 plaques) (10-fold) / (0.2 ml) = 2,500 = 2.5 x 10 3 PFU/ml stock solution

TIME COMMITMENT:

Serial dilution and pour plating takes 30-45 minutes.
Counting plaques takes 15-30 minutes.
Plates should be taken out of the incubator after the overnight incubation. If desired, cover the rim with a strip of parafilm. Sealed plates can be stored at 4’C for several weeks before counting.

MATERIALS:

Phi X 174 stock solution (should be at least 1 x 10 3 PFU/ml, but no higher than 1.5 x 10 4 PFU/ml) labeled as "tube A" (available from Carolina Biological Supply at www.carolina.com , catalog number 12-4425)
Healthy, overnight cultures of four bacterial strains, including the optimal E. coli strain C, the suboptimal E. coli strain B, and two other, non- E. coli strains.
12 tryptone base agar plates per student group
12 x ml tryptone soft-agar tubes per student group
sterile 1 ml and 5 ml pipets
sterile, distilled water
sterile snap-cap culture tubes
Kimwipes or paper towels

EQUIPMENT:

TROUBLESHOOTING TIPS:

Using a cell counter will make counting easier. Placing the plates onto a grid may also help.