Disinfection and Sterilization

Sterilization and disinfection

Disinfection The process that reduces the number of pathogenic

microorganisms. Bacterial spores and other relatively resistant organisms may remain viable.

Sterilization a treatment that destroys all microbial life,

including vegetative form and endosporesBacteriostasis to inhibit the growth of bacteria

Antisepsis:A chemical agent safely used in or on living tissue to destroy microorganisms.

Asepsis:a condition in which living microorganisms are absent.

Aseptic techniques: measures taken to ensure that living microorganisms are absent.

METHODS

Physical methods of disinfection and sterilization

Chemical methods of disinfection and sterilization

Section 2 Physical controls on microoganisms for disinfections and sterilization

Including:

Heat Cold Drying Radiation Filtration Osmotic strength

Dry heat

Hot air sterilization Flaming

Incineration

Hot air sterilization

Conditions

160-170℃, 1-2hrs Significance & applications

glassware, metal objects

Moist heat

Moist heat Boiling water

Autoclaving

Pasteurization

burning method(incineration) flowing steam disinfection

hot air drying method( 烤箱 )boiling water disinfection

Moist heat

Pasteurization

Definition: a process in which fluids are heated at temperatures below boiling point to kill pathogenic microorganisms in the vegetative state without altering the fluid’s palatability.

Conditions: 62℃, 30min or 71.7℃, 15sec

Significance: kills vegetative pathogens

Applications: milk, beer

Boiling:

100 at 1 atmospheric pressure℃ 5min killing most non-sporing bacteria For 1-2h will kill a few sporing microoganisms 2% sodium carbonate can enhance the

efficiency ,105 (the boiling point)℃

Steam sterillization with common pressure:It applies water vapor to disinfect 100 for 15℃ ～ 30min, not useful for spore

Fractional sterilization:It takes water vapor intermittently to sterilization at common pressure.it usually applies to medium containing sugar or milk,which cannot bear high temperature

Autoclaving Conditions: When pressure is 102.97~137.30kpa, the temperature in the autoclave can reach 121ºc, 15~20 minutes is enough for sterilization

Significance:

kills both spores and vegetative microorganismsthe most common and effective method of sterilizationApplication:

sterilizes materials not damaged by heat and moisture

Comparison

Moist heat is generally more effective than dry heat Reasons

Steam is more easily to inactivate proteins. (H bonds)

Steam penetrates more easily.

Steam has potent heat.

Radiation

Ultraviolet radiation The most effective wavelengths: 250-260nmMechanism: destroy DNA by forming thymine dimersCharacteristics:

poor penetrating power damage of the eyes and the skin

Applications: Air disinfectionsSurface disinfection

Filtration

Mechanism

mechanically removes microorganisms Application

sterilize materials likely to be damaged by heat

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滤菌过程

Chemical antimicrobial methods

Mechanisms Injury of cell membranes

Inactivation of proteins (e.g., enzymes )

Damage of genetic materials

Chemical antimicrobial methods Common chemical agents

PhenolSoaps and detergents Alcohols: 70-75%

Heavy metals: Silver nitrate (1%) Chlorine Iodine Aldehydes: 37% Formalin

Dyes: crystal violet

The effects types of disinfectants

Effects level Disinfectants examples

High level Ethylene oxide, peracetic acid ,kinds of aldehyde

Normal level Kinds of alcohol, kinds of iodine, chloric disinfectants

Low level Chlorhexidine, phenolic disinfectants

Factors influencing antimicrobial activity the concentration and kind of an agent used

the length of exposure to the agent

the temperature at which the agent is used

the number of microorganisms present

the kinds of microorganisms present

the nature of the material bearing the microorganism

Biological methods

Antibiotic

Bacteriocin

Bacteriophage

Some question

Question: What is the Mechanisms of the Chemical

antimicrobial methods

TERMS EXPLAINATION:Sterilization 、 disinfection 、 Bacteriostasis 、 AntisepsisAsepsis 、 Aseptic techniques