Steam exposure of a material at 100°c for 20 minutes for three consecutive days is known as

– the process by which most bacterial forms in non-living objects are destroyed, without necessarily destroying saprophytes and bacterial spores

refers to the use of chemical agents on skin or living tissues to inhibit or eliminate disease producing microorganism

a gradual process and the kinetics of death are exponential

the relationship between sterilization and the temperature of exposure is expressed in terms of

the time required to kill a suspension of microorganism at a predetermined temperature in a specified environment

MECHANISMS OF THERMAL INJURY

1.strand breaks in the bacterial DNA2.Loss of integrity of the membrane3.Denaturation of proteins4. Oxidative damage5. elevated levels of electrolytes

Preferred over dry heat because of its more rapid killing action

In moist heat

destroyed at 120 0C for 4 mins or 5.5 hrs at 100 0C

Kills all vegetative forms of microorganisms at 80 – 100 C but not bacterial spores

- Used to sterilize materials that would be damaged by autoclaving- The material to be sterilized is exposed to live steam for 30 mins for 3 consecutive days

FRACTIONAL STERILIZATION (TYNDALLIZATION)

- used in the processing of milk, foods and other beverages- only inactivate disease producing microorganisms

Expose milk at high temperature of _________followed by rapid cooling

-Used in the sterilization of surgical instruments and bandages, culture media and other contaminated
materials

Steam under pressure (auto calving)

4. STEAM UNDER PRESSURE (AUTOCLAVING)- the steam is confined in a closed vessel pressure

How many minutes to sterilize the material in autoclave

- requires higher temperature and longer period of exposure- effectiveness depends on the ability of heat to penetrate the material to be sterilized

Most widely used type of dry heat

Dry heat use to sterilize

powders, oils, jellies and

glassware

Other useful forms of dry heat

a. incineration b. open flame

oDeprive the organism of moistureoBacterial spores are not destroyed

oUsed in the preservation of foods

oNot reliable because spores are not destroyed
oMany microorganisms can survive low temperatures

– a technique of preserving microorganisms by rapid freezing and dehydrating it in high vacuum and stored under vacuum in sealed ampule in cold storage

A.ULTRAVIOLET LIGHT (UVL) oMost effective wavelength =

Ultra violet oOptimum wavelength

Radiation mechanism of actions

disrupts H bonds in microbial cell  formation of thymine dimers

lethal frameshift mutations

oUsed in sterilization of enclosed areas

oHas greater penetrating ability than UVLoPotentially hazardous to human cells

Ionizing radiation mechanism of actions

formation of free radicals  chemically interact with proteins & nucleic acids

 cell death

oForm of mechanical sieving  physical separation of microorganisms from the fluid

oUtilizes cellulose ester filters

Filtration

o0.22 um pore size – can filter almost all microorganisms EXCEPT

viruses, Mycoplasma, Chlamydia &

Rickettsia

oBased on the principle of osmosis

Mechanism of action of osmotic pressure

When the concentration of the solution surrounding the bacterial cell is altered  collapse of the bacterial cell or may become
turgid

Mechanism of ultrasonic vibration

passage of sound through the liquid  produce alternating pressures  cavities form in the liquid  cavities grow in size  burst

 cells disintegrate

FACTORS AFFECTING DISINFECTION

1.Concentration of chemical agent2.Time3.Temperature4.pH5.Nature of the medium

6.Nature of the organism

used as the standard in the evaluation of new chemical agents

designed to determine the ratio of the highest dilution that will kill the organism within a specified time to the greatest dilution of phenol showing the same result

MECHANISMS OF ACTION OF CHEMICAL AGENTS

Interfere with normal membrane function  release of small metabolites and interfere with active transport and energy metabolism

Damage of the cell membrane

– quarternary ammonium compounds - cause disruption of membrane & loss of membrane permeability - denatures proteins - most effective at alkaline pH

- cause disruption of lipoprotein framework of the membrane - most effective at acid ph

- e.g. soaps & detergents

- cause leakage of cell contents - includes phenol and cresol

highly toxic to human cell

– phenol derivative - less toxic & more potent than phenol

- e.g. lysol & creolin

disorganize lipid structure by penetrating into the hydrocarbon region

AGENTS THAT DENATURE PROTEINS

a. acids & alkalis – alters the pH of the organism’s environment b. alcohol & acetone

c. phenol & its derivatives

poison the enzyme activity by forming mercaptides with the SH groups of cysteine residues

useful as antiseptics but not as disinfectants

used in Crede’s prophylaxis

inactivates enzymes by converting functional SH groups to oxidized S-S form

Oxidizing agents includes

1. Halogens 2. Hydrogen peroxide

– considered the best antiseptic - bactericidal, sporicidal, fungicidal, virucidal & amoebicidal

– used as water disinfectant
- used in sanitizing food & dairy processing equipments

– weak antiseptic - used in cleansing of wounds, surgical devices & contact lenses

- used in the treatment of dermatologic lesions - used in staining bacteria

a. – highly selective for gram (+) bacteria e.g. crystal violet, malachite green

A kind of dye used as wound antiseptics

FormaldehydeGlutareldehyd

Ethelyne oxide

- sporicidal -used in preserving specimens &in the preparation of vaccines - used to destroy M. tuberculosis in sputum & fungus in athlete’s foot - used in the treatment of

textiles

- sporicidal - 10 times more effective than formaldehyde

- used as cold sterilant for surgical instruments especially respiratory therapy instruments

- sporicidal - used in gaseous sterilization of materials that would be damaged by heat like polyethylene tubes, electronic & medical equipments, biologicals & drugs

- slow acting

– the process of completely destroying all microbial forms, including bacterial spores