Sterilization and Disinfection

Xiao-Kui Guo PhD

Content

Basic terms and general mechanism Physical agents Chemical agents Affecting factors

Section A

Basic terms and general mechanisms

Basic terms

Sterilization 灭菌 : A physical or chemical process that completely destroys

all microbial life, including spore

Disinfection 消毒 :Only destroy the diseases-producing microorganisms

and the spore are sometimes not included

Bacteriostasis 抑菌 The property that is able to inhibit bacterial multiplication and

the multiplication will resume upon when the inhibition agent is removed.

Antisepsis 防腐 A biocide or production that destroys or inhibits the growth of

microorganisms in or on living tissue

Asepsis 无菌 The absence of pathogen microbes

Basic terms

The general mechanisms

DNA

-SH -SS-

Damage to DNA

Protein denaturation

Removal of free sulfhydryl groups

Chemical Antagonism

Disruption of cell membrane or wall

Section B

Physical Agents

The element of physical agents

Physical agents

Radiation辐射辐射

Heat

Filtration过滤过滤

Ultrasonic

Freezing

Dry heat

Moist heat

Ultraviolet Radiation

microwave

Ionizing Radiation

Heat

Temperature

The growth state of the bacteria

changes with the temperature

Heat Dry heat

Mechanism: the denaturation and coagulation of protein

Methods: Hot air sterilization 干烤 Incineration焚化 red heat赤热 Flaming赤热

Heat Moist heat

Mechanism: as same as dry heat but more effective Autoclaving: 121 ,103℃ .4kPa, 20min

cidal for both vegetative organisms and endospores Boiling water Pasteurization: to kill particular spoilage organisms or

pathogens flash method: 71.7°C, 15~30s holding method: 61.1~62.8 , 30 min℃

The hot stream surrounding the

bodies of bacteria makes the moist

heat a more effective mean for killing

Heat Moist heat

fractional sterilization间歇蒸气灭菌法 Steam heating to 100 °C for 30 min Vegetative cells are destroyed but endospores survive Incubate at 30 °C -37 °C overnight

Most bacterial endospores germinate Second heat treatment, 100 °C, 30 min

Germinated endospores are killed. Second incubation at 30°C-37 °C overnight

Remaining endospores germinate Third heat treatment, 100 °C, 60 min

Last remaining germinated endospores are killed

Radiation Ultraviolet

Mechanism: Ultraviolet leads to the formation of adjacent two thymine to form dimer.

The most effective wavelength is in the 240 to 280nm with the optimum at about 260nm

The thymine-thymine dimer

Even if faces the glass or paper, the Ultraviolet

can not penetrate

Radiation

Ionizing RadiationX-rays and gamma rays more energy and penetrating power than UVused to sterilize pharmaceuticals and disposable m

edical supplies such as syringes, surgical gloves, catheters, and sutures

used to retard spoilage in seafoods, meats, poultry, and fruits

Filtration The heat destroys the bacteria and meanwhile the

useful ingredient doesn’t survive. Filtration set a barrier to keep out the particle at a l

ow temperature Diameter of the pores: 0.22~0.45μm

Water and gas can pass the

barrier

Particle, including bacteria, keeping out

Ultrasonic

Ultrasonic

To form cavities about 10 μm in dia

meter in liquid

The cavities collapse of the pressure of 10

00 atmosphere

The cavitation produces a number of chemical and physical changes i

n medium.

Causing a depolymerization of macromolecules and intra

molecular regrouping

Hydrogen peroxide produced

Bacteria killed

•Because there are numerous survivors after the ultrasonic treatment, so it is of no practical value in sterilization and disinfection

Freezing

Although many bacteria are killed by exposure to cold, freezing is not a reliable method of sterilization.

The primary use is in the preservation of bacteria.

The best way to preserve the bacteria nowadays is lyophilization冷冻干燥 .

Section C

Chemical Agents

Chemical agents I:

Phenol and phenol derivatives alter membrane permeability and denature proteinschlorhexidine ineffective against endospores

Chemical agents II:

Soaps and detergentsAnionic (negatively charged) detergents: mechanic

ally remove microorganisms and other materials but are not very microbicidal.

Cationic (positively charged) detergents: alter membrane permeability and denature proteins; ineffective against endospores, M. tuberculosis, and P. species.

Chemical agents III:

Alcohols denature membranes70% solutions of ethyl or isopropyl alcohol ineffective against endospores and non-enveloped

viruses

Chemical agents IV:

Heavy metalsdenature proteinsMercury compounds (mercurochrome; merthiolat

e) : bacteriostatic, ineffective against endosporesSilver nitrate (1%) : put in the eyes of newborns to

prevent gonococcal ophthalmia.

Chemical agents V:

Chlorine reacts with water to form hypochlorite ions, which in

turn denature microbial enzymes Iodine and iodophores

denatures microbial proteinseffective against some endospores

Chemical agents VI:

Aldehydesdenature microbial proteinsFormalin (37% aqueous solution of formaldehyde

gas)glutaraldehyde: kill vegetative bacteria in 10-30 mi

nutes and endospores in about 4 hours

Section D

Affecting factors

Factors Influencing Antimicrobial Activity The concentration and kind of a chemical agent used; The intensity and nature of a physical agent used; The length of exposure to the agent; The temperature at which the agent is used; The number of microorganisms present; The species or strain of microorganism; The nature of the material bearing the microorganism; The presence of organic or other interfering substances.

The End

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