– 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
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
– 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
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
– 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 |