Sterilization, disinfection and antisepsis BC Yang Two very original methods for disinfection
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Sterilization, disinfection and antisepsis
Two very original methods for disinfection or BC Yang
For lecture only
In 1866 J Lister suggested antiseptic surgery. His rational was: Putrefaction is caused by microbes Wound sepsis is a form of putrefaction Wound sepsis is caused by microbes Carbolic acid, phenol BC Yang
Carbolic acid, phenol: a toxic white soluble crystalline acidic derivative of benzene
various antiseptics various disinfectants
various germicides
adhesive dyes
perfumes
textiles
lubricating oils
Acute poisoning by ingestion, inhalation or skin contact may lead to death. Phenol is readily absorbed through the skin. Highly toxic by inhalation. Causes burns.
In the previous year Lister had heard that 'carbolic acid' was being used to treat sewage in Carlise, and that fields treated with the affluent were freed of a parasite causing disease in cattle.
Lister then began to clean wounds and dress them using a solution of carbolic acid. He was able to announce at a British Medical Association meeting, in 1867, that his wards at the Glasgow Royal Infirmary had remained clear of sepsis for nine months.
Opposition was great In England and the United States mainly against Lister's germ theory rather than against his "carbolic treatment."
Phenols and phenolics
Carbolic acid
Low level disinfectant
O-phenylphenol (Lysol)
Hexachlorophene (Phisohex)
High level for Staphylococcus sp. and
Streptococcus sp.
Surgical scrubs
Damage membrane, inactive enzymes, denature proteins
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BC Yang
The day after SARS
蚊子少了
;
人離的遠了
;
官員被糾正
;
化學兵正當紅
• Ethylene oxide: denatures proteins • Highly penetrating • Most used in hospitals for plastic ware, textiles, etc…..
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BC Yang
Mechanism of antimicrobial action
Damage to DNA: radiation, UV, DNA reactive agents
Protein denaturation: Heat, pH, metals
Disruption of cell membrane or cell wall: detergents, enzymes
Chemical antagonism: analogs
Removal of free sulfhydryl groups: oxidizing agents
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BC Yang
To die or not to die, that is a question
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Sepsis: microbes contamination
Asepsis: absence of microbes contamination
Sterilization: 100% killing
Disinfection: loss the ability to cause disease
-cide or cidal: killing of microorganism
-static or stasis: inhibit growth or multiplication of microbes BC Yang
Types of antimicrobial agents
• Physical – Heat – radiation • Chemical – Vapors – selectivity
Scientific American284 (5):54-61
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BC Yang
Killing is a probability
Die at a constant rate (logarithmically) Depend on exposure time and microbial load Rare will reach 100% (on purpose and money consuming)
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BC Yang
Parameters of sterilization/disinfection
Action process
The rate/kinetics
: the death rate of a microbial population follows a logarithmic path.
Resistances
: pure empirical, varied from culture condition, nature of the environment
Control/indicators
:
Living:
heat : spores, themophilic bacteria
ethylene oxide and radiation: Bacillus subtilits var. nigar.
Chemical: succinic anhydride (120 o C), sulphur (115 o C); color change; etc..
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BC Yang
Action index
A spoonful work already well?
Why not LD 50 ?
Phenol coefficient (PC)
American official analytical chemist’s use-dilution method
Staphylococcus aureus, Pseudomonas aeruginosa, Salmonella choleraesuis
Filter paper method
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BC Yang
The phenol coefficient (PC)
A water-soluble phenol-based disinfectant (amphyl, lysol) is tested for its bactericidal effectiveness as compared with phenol.
These disinfectants are serially diluted in a series of salmonella cultures and incubate for a while.
Chemicals with lower phenol coefficients have greater effectiveness
Restricted to phenolics PC= Greatest dilution of the phenolic that kills Test bacteria in 10 min, but not in 5 min Greatest dilution of phenol giving same result
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BC Yang
As a matter of temperature
Heat
Boiling water Moist heat (steam under pressure, autoclave) Hot-air sterilization (Oven) Pasteurization Tyndallization Incineration
Low temperature
Refrigerator temp (4-7oC) Deep-freeze (-20oC to -40oC); liquid nitrogen (-196oC) Lyophilization (desiccation in low temperature) For lecture only
BC Yang
Pasteurization
Suggested by L. Pasteur It is used to render mild safe (tuberculoses) and extend its storage quality Keep the flavor of milk, wine 62 o C 30 min, 71 o C for 15 sec
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BC Yang
Pasteurization
別呆了
,
不要喝尚青尚新鮮的牛奶
!
•
1909 John Ross Robertson finances the installation of Toronto's first milk pasteurization plant in the College Street hospital, 30 years before it becomes mandatory.
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BC Yang
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Tyndallization (Fractional sterilization)
John Tyndall was a man of science—draftsman, surveyor, physics professor, mathematician, geologist, atmospheric scientist, public lecturer, and mountaineer.
For killing both vegetative and spore forming bacteria at temperature of 100 o C or below for 30 min on the consecutive days BC Yang
Filtration
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BC Yang
Filtration
Liquid
When subjects are heat-labile
0.22/0.45 mm membrane filter
Air
Large space Alternative: electrostatic precipitation
Particles passed through a high voltage electric field become charged, and attracted to and held by the plate of opposite potential (remove ~97% of bacteria)
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BC Yang
Surfactants: breaks oily film on skin
Wash away: do you really clean your hands?
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BC Yang
UV radiation
Ultraviolet is light with very high energy levels and a wavelength of 200-400 nm. One of the most effective wavelengths for disinfection is that of 254 nm.
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BC Yang
Alcohols
High level disinfectant
Disrupt protein, disrupt membranes, dissolve lipids
70% ethanol
Used in tinctures
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BC Yang
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Halogens (Iodine)
Iodine combines with tyrosine & oxidized SH groups on other amino acids
Tincture: 1-2% I2 + 2% Na2I in 70% ethanol (for surgical site disinfection).
Povidone-iodines: Betadine
Skin disinfection
Surgical scrub BC Yang
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The choices?
It always depends!
The materials
The purpose
The nature of microbes
BC Yang