Module 3, Experiment 3:
Aseptic Technique & Culturing Microbes
Part 3: Generating Microbial Cultures:
Observe your culture tubes after 24 hours to assess the growth patterns of all tubes.
If there is no observable growth allow the tubes to incubate an additional 24 hours.
Record your observations here.
Attach a picture of you incubator in this space.
A. What is the difference between a bactericidal and bacteriostatic agent? Between sterilization and disinfecting?
Bactericidal agent refers to substances used to kill bacteria while bacteriostatic agent refers to substances used to restrict or to inhibit bacteria cells growth.
Sterilization is the complete destruction or elimination of all viable organisms in or on an object while disinfection is the destruction of pathogenic nonsporulating microbes or their toxins usually on inanimate surfaces.
B. List five sterilization methods, how they work, and what they are used for.
Autoclaving (steam under pressure or pressure cooker) at 121oC for 15 minutes (15lbs/in2 pressure) is good for sterilizing almost anything; however, autoclaving will denature or destroy heat-labile substances. Dry heat (hot air oven) at 160oC for 2 hours or 170oC for 1 hour is used for glassware, metal, and objects that will not melt.
Incineration burns organisms and physically destroys them. This method is used for needles, inoculating wires, glassware, etc. Boiling at 100oC for 30 minutes kills almost all endospores. Very long or intermittent boiling is required to kill endospores and sterilize a solution.
Toxic chemicals and gas such as formaldehyde, glutaraldehyde, and ethylene oxide can kill allforms of life in a specialized gas chamber.
C. What is pure culture? Why is it important to work with a pure culture?
A pure culture is one in which all the organisms are descendants of the same