Question

1. Why should cotton provide an effective barrier against air contaminants, when the spaces between threads are relatively large? 2. What other ways might be used to close test tubes, still retaining a sound bacteriologic technique? 3. How would you protect culture medium from lint in a liter Erlenmeyer flask in which the cotton plug had to be large? 4. Explain your preference of method for the sterilization of : A hypodermic needle, rubber gloves, talcum powder, paraffin oil, a soldered test tube rack of metal plugged test tubes, a package of surgical gowns, an egg medium discarded glassware to be washed, bottles of water, and a solution of dextrose. 5. How would you sterilize a bottle with screw top cap in the autoclave? 6. How would you prove that the apparent sterility of cultures made from suspensions of bacteria in a disinfectant was due to the death of the organisms and not to the disinfectant carried over to the medium? 7. Consult the characteristics of the following genera, and draw each shape with its size: 1) Escherichia coli 2) Bacillus cereus. 3) Micrococcus luteus 8. Why agar is preferentially used in solid media? Are there any others that can be substituted for agar?

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Answer 1

1. in general cotton will not allow outside air containing microbes to enter the medium or vessel. cotton plugs preserve the culture's integrity through the allowance of air flow, while shielding the culture from dust and other microorganism.