To pour plates:
1. Turn on the laminar flow hood. Wipe the outside of the bottle of medium and the inside of
the laminar flow hood with disinfectant.
2. Stack labeled Petri plates in threes beside the edge of the tabletop or hood top.
3. Remove the medium bottle cap and “flame” the bottle top (pass bottle top through the hot
part of the flame three times).
4. Open the bottom Petri plate of the first stack. Pour agar over one-half the height of the Petri
plate. Tilt the plate slightly to cover the bottom with agar.
5. Repeat pouring of the other plates and other stacks of plates.
6. Stack groups on top of each other.
7. Leave undisturbed for at least 15 minutes. Keep plates closed until ready to use.
8. Allow drying in a clean area, undisturbed, for at least 24 hours before use. Plates are good for
about 2 weeks if stored in a cool, dark place.
Data Analysis/Conclusion
Evaluate your ability to pour plates with about 15 to 20 mL of LB agar. Consider the final
volume (about 20 mL) of agar in the plate, coverage (equally covering bottom), lumpiness (none),
contamination (cloudy or fuzziness in culture), and labeling of the plate. Describe which of these
tasks you did well, and which you could improve upon and how.
Thinking Like a Biotechnician
1. Name five things you can do to decrease the chance of contaminating a sample.
2. When pouring plates, you notice that the agar is coming out in lumps. Why is this
undesirable and what corrective measures can you take?
3. LB agar plates are needed for several days of lab work. If eight sleeves of Petri plates (20
plates/sleeve) are need, each poured with about 20 mL, what total volume of LB agar should
you prepare?
DNA Isolation and Analysis
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