Lecture Set 3 : Part 6 Flashcards
what are the general principles of growth control?
-sterilization
-inhibition
-decontamination
-disinfection
what is the principle of sterilization?
-killing or removal of ALL viable organisms from an object or growth medium
-includes endospores
-if the object or medium is left untouched, nothing will grow
what is the principle of inhibition?
-effectively limiting microbial growth without killing
-the thing that is inhibiting growth can be removed and growth can resume
what is the principle of decontamination?
-treatment that makes the object SAFE to handle
-may still contain pathogens (difference from disinfection)
-lower level
what is the principle of disinfection?
-treatment that aims to remove pathogens but not necessarily destroy all microbes (not sterile)
-high level
what is the most widely used method of controlling microbial growth?
-heat
why is heat used to control microbial growth?
-high temperatures will denature proteins and other cell structures
-gives a killing effect because proteins are required from growth (DNA replication)
what is decimal reduction time?
-the amount of time required to reduce viability tenfold
-the lower it is, the faster the killing is (higher temps = faster death)
-highly specific to environmental conditions because they affect how the heat penetrates (dry vs moist heat) and the medium (juice vs water)
-dry = worse penetration
-moist = better penetration
what is pasteurization?
-process of using precisely controlled heat to reduce the microbial load in heat-sensitive liquids
-does not kill all organisms so is not sterilization
what is the pasteurization of milk?
-has several time and temperature combos
-low temperature/long time (63 for 30 minutes)
-high temperature/short time (72 for 15 seconds)
-both processes kill coxielle burnetii
what is coxielle burnetii?
-causative agent of Q fever
-most resistant pathogen found in milk
what is the autoclave?
-a sealed device that uses steam (moist heat) under pressure to sterilize materials
-typically set to 121 degrees and 15 pounds per square inch of pressure for 15-20 minutes
-all materials must reach an internal temp of 121 to sterilize (time it takes depends on shape and size of object)
-sufficient to destroy the endospores of geobacillus stearothermophilus
how is radiation used to control microbial growth?
-short wavelength radiation (gamma, x-ray, and uv) can damage DNA and destroy microorganisms
-gamma and x-rays penetrate directly through materials (sterilize equipment in plastic packaging + can be used to prolong shelf life of food)
-uv does not penetrate well (useful to decontaminate lab surfaces + can be used along with chlorine for drinking water treatment)
how is filtration used to control microbial growth?
-membrane filters are fine filters with 0.45, 0.22, or 0.1 micrometer pore size
-allows liquid to pass but restricts bacteria passage (air as well)
-used to remove microbes from temperature sensitive liquids (some media ingredients (MgSO4), antibiotics, enzymes, and vaccines)
how do you decide what filter size to use?
-size of bacteria
-smaller is not always better (takes more time for stuff to filter through)
what are chemical antimicrobial agents?
-sterilants
-disinfectants
-sanitizers
-antiseptics
what are sterilants?
-destroy all microorganisms including endospores
-ex: ethylene oxide (gas used to sterilize some temp. sensitive lab equipment)
what are disinfectants?
-kill microorganisms but not all endospores
-ex: chlorine bleach (used to disinfect lab surfaces)
what are sanitizers?
-less harsh than disinfectants
-used to reduce microbe numbers
-ex: 70% ethanol hand sanatizer
what are antiseptics?
-kill or inhibit growth of microorganisms but are sufficiently non-toxic to be applied on living tissue
-ex: iodine (used for small cuts)
what are the different classifications of antimicrobial agents?
-bacteriostatic
-bacteriocidal
-bacteriolytic
what does bacteriostatic mean?
-prevents cell growth as long as the antimicrobial agent is present (just inhibits growth)
what does bacteriocidal mean?
-kills the cells but does not lyse them
-ex: adding formaldehyde
what does bacteriolytic mean?
-kills the cells and lyses them
