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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:



Putrefaction is caused by microbes
Wound sepsis is a form of putrefaction
Wound sepsis is caused by microbes
Carbolic acid, phenol
For lecture only
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

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
For lecture only
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…..
For lecture only
BC Yang
Mechanism of antimicrobial action

Damage to DNA: radiation, UV, DNAreactive 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
For lecture only
BC Yang
To die or not to die, that is a
question






For lecture only
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
For lecture only
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)
For lecture only
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 (120oC), sulphur
(115oC); color change; etc..
For lecture only
BC Yang
Action index

A spoonful work already well?

Why not LD50?

Phenol coefficient (PC)

American official analytical
chemist’s use-dilution method

Staphylococcus aureus,
Pseudomonas aeruginosa,
Salmonella choleraesuis

Filter paper method
For lecture only
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
Greatest dilution of the phenolic that kills
Test bacteria in 10 min, but not in 5 min
PC=
For lecture only
Greatest dilution of phenol giving same result
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



For lecture only
Refrigerator temp (4-7oC)
Deep-freeze (-20oC to -40oC); liquid nitrogen (-196oC)
Lyophilization (desiccation in low temperature)
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
 62oC 30 min, 71oC
for 15 sec
For lecture only
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.
For lecture only
BC Yang
Tyndallization
(Fractional sterilization)
For lecture only

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 100oC or below for
30 min on the consecutive days
BC Yang
Filtration
For lecture only
BC Yang
Filtration

Liquid



When subjects are heat-labile
0.22/0.45 mm membrane filter
Air

Large space
Alternative: electrostatic precipitation

For lecture only
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
For lecture only
do you really
clean your
hands?
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.
For lecture only
BC Yang
Alcohols
 High
level disinfectant
 Disrupt
protein, disrupt membranes,
dissolve lipids
 70%
ethanol
 Used
in tinctures
For lecture only
BC Yang
碘酒 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
For lecture only
BC Yang
The choices?
It always depends!
 The
materials
 The purpose
 The nature of microbes
For lecture only
BC Yang