sterilization disinfection Dr Dunith Liyanagamage MBBS Agents infect
sterilization & disinfection Dr. Dunith Liyanagamage (MBBS)
Agents infect bacteral growth • Physical agents • Temperature, radiation, filtation • Chemical agents • disinfector • Biologycal agents • antibiotics
Disinfection • killing, or removal of M. that may cause disease • not including spores
Sterilization • Completely destroys or removes all microbial life • including spores, nonpethogens
Aseptic • Absence of pathogenic microbes
Methods for control of microorganisms Physical methods Heat Hot-air sterilizer Autoclaving Radiation Filtration Ultrasound Dryness Low temperature Chemical agents
Section 1 physical sterilization and disinfection
heat 1. 2. Dry heat Moist heat moist heat sterilizes at a lower temperature than dry heat
Dry heat • Incineration • Direct flames • Hot-air sterilizer • 160 -170 C for 2 hours----spores • Glass petri dishes and pipettes • Infrared • microwave • For glassware and materials impervious to steam • Kill of all organisms, including the spore formers
Moist heat pasteurization • Two methods: • 62 ℃ for 30 minutes • 72 ℃ for 15 -30 seconds • to kill particular spoilage organisms or pathogens • Primarily for milk
pasteurization
• boiling • 100℃ 5 min, kill vegetative organisms • Keep 1 -2 h can kill endospores • Materials that can stand boiling • steam • Steam heating to 100 °C for 15 -30 min • Can kill vegetative cells • Arnold
Arnold
fractional sterilization Steam heating to 100 °C for 30 min Incubate at 37 °C overnight Steam heating to 100 °C for 30 min • For nutrient materials which can not stand high temperature 3 cycles
Autoclaving: • pressure: 15 1 b/in 2 • temperature: 121 • held: 15 -20 minutes • autoclaves or pressure cookers • kill both vegetative organisms and endospores • The most effective
UV light • at 250 -260 nm (265 -266 nm) • absorbed by purine and pyrimidine bases of DNA • form thymine dimers • inhibit DNA replication • very poor penetrating power • To sterilize the air and any exposed surfaces • damage the cornea and skin: damage the eyes, cause burns, and cause mutation in cells of the skin
UV light
Filtration • for certain solutions that may be damaged or denatured by high temperatures or chemical agents • has a pore size of 0. 22 μm • physically trap particles larger than the pore size and retain smaller particles
A pasteurization C Hot-air sterilizer E UV light B filtration D Autoclaving 1 For milk and wine 2 For ordinary medium 3 air sterilization of burn ward, operating room 4 For serum, antibiotics 5 For dressing
• 1 For milk and wine A pasteurization • 2 For ordinary medium D Autoclaving • 3 air sterilization of burn ward, operating room E UV light • 4 For serum, antibiotics B filtration • 5 For dressing Hot-air sterilizer (moist heat)
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