B. Reagents

• YPG Petri dishes

Procedures

1. Obtain the prepared Petri dishes from the instructor and expose them to the following:
   • Expose to the air for 30 minutes
   • Touch with unwashed fingers
   • Touch with fingers washed with water and soap
   • Touch with fingers dipped in ethanol
   • Kiss with moist lips
   • Press lightly against the lab door knob
   • Press lightly against the restroom door knob
   • Smear a little yogurt
   • Smear 1 ml of milk
   • Press coins
   • Press against the bottom of a flask or beaker
   • Cough vigorously from 4-6 inches away
2. These plates should be labeled appropriately and incubated upside down at 37 & #186;C for 48 hours.

Notes

1. If culture tubes are used instead of petri dishes, cover the tubes with finger. Shake, then incubate.

Discussions

When working with microorganisms, it is important that the working environment stays as clean as possible. For example, a minuscule puff of mold spores can drift in air for an extended period of time and contaminate many subsequent experiments. Some of the spores can withstand even the temperature existing inside an autoclave and emerge from the sterilization process in dormant but viable forms. In general, the chance of contamination is proportional to the number of microorganisms in the environment when the same sets of aseptic procedures are taken. Of course, contamination means nothing but the waste of both the materials and the time spent. It can be an extremely maddening experience even for the calmest researcher. It is one's prerogative to be dirty or clean in one's own living quarters, but it is plainly irresponsible not to practice good aseptic techniques and keep the working environment clean, for not only himself but for everyone else as well. All the autoclaving will not help much in reducing the chances of contamination if the rest of the working environment is full of bugs as a result of improper attention to cleanliness. Although the presence of microorganisms cannot be totally eliminated in our lab economically, the numbers can certainly be reduced drastically by orders of magnitude. Uncleanliness simply does not pay in biochemical engineering!

Questions

1. Describe the morphology of the colonies growing on the plates (color, texture, size, shape, elevation, number of colonies, etc.)
2. You breath the air and lick your finger without much hesitation. Will you lick the plate full of microorganisms? Why?