micro lab mid term casey - Microbiology Midterm Experiment...

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Microbiology Midterm Experiment 1: Media Preparation and Sterilization Culture medium – contains nutrients, such as carbon and nitrogen, required for the cells to grow Complex medium – composed of digests of chemically undefined substances (yeast and meat extracts) Defined medium – one in which a precise chemical medium Culture mediums can be prepared two ways: broth solid medium Agar – extracted from Rhodophyta (red algae) and is a useful solidifying agent (after being heated to 100 o C and solidifies at 40-42 o C and will not melt again until temp reaches 80-90 o C) Plates solid media in Petri plates Deeps – test tubes containing solid media that has been allowed to solidify upright (used for anaerobic growth ) Slants – test tubes containing solid medium that solidify at an angle and surface of agar is used for maintenance of microorganism stock cultures Sterilization – killing or removal of all living organisms and their viruses from a growth medium Autoclave – a sealed device that allows the entrance of steam under pressure; facilitates killing of microorganisms including bacterial endospores ( liquid media ) heated to 121 o C at 15 pounds per square inch (psi) pressure for 15 minutes Dry heat sterilization – kills by oxidation effects Direct flaming – one of the simplest methods of dry heat sterilization Hot-air sterilization – sterilized by placing in an oven and heated to 170 o C for 2 hours (used for glassware) Filtration – sterilizes heat-sensitive liquids or gases ( antibiotics) ; filter is a device with pores too small for the passage of microorganisms but large enough for the passage of the liquid or gas; membrane filter is a tough disc composed of cellulose acetate or cellulose, which contains a large number of tiny holes; surface of the filter traps particles while allowing the liquid to pass through; physical removal of bacteria or other contaminants (beer is sterilized this way) Gaseous chemosterilizers – one widely used gas is ethylene oxide , which made the use of plastic Petri dishes and plastic syringes possible (toxic and explosive); it is released in a tightly sealed chamber where is circulates for up to 4 hours with the items to be sterilized
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also called cold-sterilization (no heat is used in the process) Electromagnetic radiation – (includes microwaves, ultraviolet radiation, X-rays, gamma rays and electrons) UV radiation – causes damage to DNA (thymine diameters) leading to the death of exposed organisms (cannot penetrate solid, opaque, light-absorbing surfaces, only useful to sterilize exposed surfaces) Ionizing radiation – causes ions and other reactive molecules to be produced and these reactive molecules can degrade or alter biopolymers (DNA and proteins); can be used in the food industry and for sterilization and decontamination of medical supplies ( bandages ) Experiment 2: Culturing Microorganisms from the Environment The minority of microorganisms are pathogenic (disease causing for humans), the majority
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