Transcript Microbial physiology

Sterilization, disinfection
and antisepsis
Two very original methods for disinfection
or
For lecture only
BC Yang
In 1866 J Lister suggested antiseptic
surgery. His rational was:
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Putrefaction is caused by microbes
Wound sepsis is a form of putrefaction
Wound sepsis is caused by microbes
Carbolic acid, phenol
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BC Yang
Carbolic acid, phenol: a toxic white soluble
crystalline acidic derivative of benzene
 various antiseptics
 Acute poisoning by
 various disinfectants
ingestion, inhalation or
skin contact may lead to
death.
 Phenol is readily absorbed
through the skin. Highly
toxic by inhalation.
 Causes burns.
 various germicides
 adhesive dyes
 perfumes
 textiles
 lubricating oils
 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
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Carbolic acid
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Low level disinfectant
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O-phenylphenol (Lysol)
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Hexachlorophene (Phisohex)
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High level for Staphylococcus sp. and
Streptococcus sp.
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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
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Damage to DNA: radiation, UV, DNAreactive agents
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Protein denaturation: Heat, pH, metals
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Disruption of cell membrane or cell wall:
detergents, enzymes
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Chemical antagonism: analogs
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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
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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
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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 (120oC), sulphur
(115oC); color change; etc..
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BC Yang
Action index
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A spoonful work already well?
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Why not LD50?
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Phenol coefficient (PC)
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American official analytical
chemist’s use-dilution method
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Staphylococcus aureus,
Pseudomonas aeruginosa,
Salmonella choleraesuis
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Filter paper method
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BC Yang
The phenol coefficient
(PC)
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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
Greatest dilution of the phenolic that kills
Test bacteria in 10 min, but not in 5 min
PC=
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Greatest dilution of phenol giving same result
BC Yang
As a matter of temperature
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Heat
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Boiling water
 Moist heat (steam under pressure, autoclave)
 Hot-air sterilization (Oven)
 Pasteurization
 Tyndallization
 Incineration
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Low temperature
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Refrigerator temp (4-7oC)
Deep-freeze (-20oC to -40oC); liquid nitrogen (-196oC)
Lyophilization (desiccation in low temperature)
BC Yang
Pasteurization
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Suggested by L.
Pasteur
 It is used to render
mild safe
(tuberculoses) and
extend its storage
quality
 Keep the flavor of
milk, wine
 62oC 30 min, 71oC
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
Tyndallization
(Fractional sterilization)
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John Tyndall was a man of
science—draftsman, surveyor,
physics professor, mathematician,
geologist, atmospheric scientist,
public lecturer, and mountaineer.
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For killing both vegetative and
spore forming bacteria at
temperature of 100oC or below for
30 min on the consecutive days
BC Yang
Filtration
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BC Yang
Filtration
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Liquid
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When subjects are heat-labile
0.22/0.45 mm membrane filter
Air
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Large space
Alternative: electrostatic precipitation
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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)
BC Yang
Wash away:
Surfactants: breaks oily film on skin
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do you really
clean your
hands?
BC Yang
UV radiation
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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
碘酒 Halogens (Iodine)
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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
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BC Yang
The choices?
It always depends!
 The
materials
 The purpose
 The nature of microbes
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BC Yang