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Sterilization & DisinfectionPhysical Agents
Hugh B. Fackrell
PhysSter.ppt
04/20/23
2
Sterilization & Disinfection
Definitions Bacterial Cell Death Physical methods
– Heat– Radiation– Filtration
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3
Definitions
Sterilization– Complete Destruction of ALL microbes
Disinfection– Killing of pathogens on inanimate objects– physical or chemical
Antiseptic– A chemical agent for disinfection of living tissue– External skin, mouth vagina
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Definitions
Bacteriocide – kill microbes– also germicide, fungicide, virucide
Bacteriostatic– Prevents or stops microbial growth– also fungistatic, virustatic
Aseptic(Asepsis)– Prevent contamination of person or object by microbes
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Definitions
Sanitize– Removal of pathogens from inanimate objects– Mechanical or chemical cleaning– need not sterilize of disinfect
Contamination– Presence of living microbes on object
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Definitions
Infection– Presence of living multiplying microbes in host
tissues– often pathogenic
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Bacterial Cell Death
Time (min)
Survivors
(log)
0
1
2
3
4
5 1 log decrease = 90% kill
1 log Death rate (D) varies with bacteriocide
D Time(min) to kill 90%
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Physical Methods
Heat Radiation Filtration
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Heat Sterilization
Factors – length of exposure– temperature
“Moist Heat” “Dry Heat”
Method of choice
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10“Moist” heat
Effective quickly against most pathogens – low thermal death point– 60-70% in 10 min
Pasteurization 60-70 oC Sanitizes Hot water 60-100 oC Disinfects Steam 15 psi 121oC Sterilizes
Endospores resist boiling for hours!!
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11Heat: Mechanism of Action
Inactivation of enzymes Structural changes
– coagulation of proteins
Oxidation – membrane disruption
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12Pasteurization Liquids Minimal heat
– 145 oF (62.9 oC) - 30 min
– 162 oF (71.6 oC) - 15-30 sec
Flavour of drink preserved Kills non spore forming pathogens
– TB. Brucella, Salmonella, Streptococcus
Kills spoilage bacteria– Lactobacillus, Streptococcus
04/20/23
13“Flash” Pasteurization
72 oC - 15 sec 88 oC - 1 sec 90 oC 0.5 sec 96 oC 0.05 sec
Heating coil Cooling coil
Raw milk
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14Boiling Water
100 oC (212 oF) 10- 30 min Disinfectant
– spores & some viruses are resistant
Safe for clean instruments that DO NOT penetrate the tissue
Soiled items -add detergent
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15Steam Under Pressure
Autoclave 15 psi 121 oC 250 oF Time 15 min - dependent on volume Steam displaces air & penetrates
– Packing of autoclave critical!
Airlocks in packing– reduce effective temp & pressure
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16Dry Heat
Longer & hotter Oxidation Carbonization
– cotton plugs
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17Types of Dry Heat
Oven– 160-165 oC 2 hours– 170-175oC 1 hr– Glass, oils, waxes, glycerin
Incineration– destruction of pathological material
Flaming– used as aseptic techniques– scissors, scalpels, loops, needles
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Radiation Sterilization
Ionizing RadiationUltraviolet Radiation
Point mutations involve changes in only one or a few nucleotides
*
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Radiant Energy spectrum
Ionizing
Radiation
UV lightIncreased
energy
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20 Sterilization by
Ionizing Radiation Gamma Rays
– Food– Plastics
Electron Beams– pharmaceuticals
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Ionizing Radiation
Creates free radicalsCauses breaks in two DNA strands
–Results in deletions
–Results in translocations
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Free Radicals
High Energy Radiation–energy absorbed by atoms
–energy added to electrons
–electrons ejected from atoms
–leaves ionized atoms & unpaired electrons
Free radicals can breaks both phosphodiester bonds of a DNA helix
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23Sterilization by Ultraviolet light
Circulating air Surfaces
– benchtops
Small samples of liquid
Surfaces only poor penetration
Photoreactivation
white light reverses effect of ultraviolet
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Ultraviolet Radiation
Pyrimidine dimers
–errors during repairPeroxides, Free radicals
–See ionizing radiationDirect molecular damage
–intense exposure
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Repair of thymine dimer
GTA T GTCCATAACAG
GTA TTGTCCATAACAG
CATAACAG GTA GTC
TT
TTGT GTCCATAACAG
A
GT GTCCATAACAG
TTA G
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26Filtration Sterilization
HEPA filters
– High Efficiency Particulate Air filter
– Remove airborne microbes• Filters particles >0.3 m
– Operating rooms
– “Clean rooms” instrument assembly
– Burn patients
– Immunocompromized
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27Filter sterilization
Membrane filters– cellulose nitrate or synthetic polymers
Pore size– bacteria 0.22m 0.45 m– viruses 0.01 mm
Sterilize heat or energy sensitive materials– bacterial media– drug solutions