- 1. Disinfection
- Disinfectionis the elimination of pathogens, except spores,
frominanimateobjects
- Disinfectantsare chemical solutions used to clean inanimate
objects
- (physical processes, e.g., UV radiation, may also be employed
to effect disinfection)
- Germicidesare chemicals that can be applied to both animate
(living) and inanimate objects for the purpose of eliminating
pathogens
- Antisepticsare formulated for application to living tissue
www.freelivedoctor.com 2. The Ideal Disinfectant
- Resistant to inactviation
- Broadly active (killing pathogens)
- Not poisonous (or otherwise harmful)
- Penetrating (to pathogens)
- Not damaging to non-living materials
www.freelivedoctor.com 3. Disinfectant Performance
- Is dependent on Disinfectant concentrations
- Is dependent on length (time) of administration
- Is dependent on temperature during administration
- (usual chemical reaction 2x increase in rate with each 10 C
increase in temperature)
- Microbe type (e.g., mycobacteria, spores, and certain viruses
can be very resistant to disinfectionin general vegetative cells in
log phase are easiest to kill)
- Substrate effects (e.g., high organic content interferes with
disinfectionstainless steel bench easier to disinfect than
turd)
- It is easier (and faster) to kill fewer microbes than many
microbes
www.freelivedoctor.com 4. Cleansing
- Cleansingis the removal of soil or organic material from
instruments and equipment & may be done, clinically, in four
steps:
- Rinsing the object undercold water
- Applying detergent and scrubbing object
- Rinsing the object under warm water
- Drying the object prior to sterilization or disinfection
www.freelivedoctor.com 5. Sterilization
- Sterilizationis the total elimination of all microorganisms
including spores
- Typically the last things to die are the highly heat- and
chemical-resistant bacterial endospores
- Instruments used for invasive procedures must be sterilized
prior to use
- Moist heat or steam, radiation, chemicals (e.g.,
glutaraldehyde), and ethylene oxide (a gas) are employed for
sterilization
- Sterilization by autoclaving, which uses moist heat, is used in
most hospital and microbiology laboratory settings
www.freelivedoctor.com 6. Phenol, Carbolic Acid, &
Phenolics
- Phenol (carbolic acid) and derivatives
- Affect plasma membrane, inactivates enzymes, and denature
proteins
- Stable, persistant, and especially effective when dealing with
disinfecting materials contaminated with organics
- but leave residual films, can irritate skin, dont kill
endospores, and are corrosive to rubber and plastics
- Some phenolics are mild enough for use as antiseptics while
others are too harsh or otherwise dangerous to be employed on
living tissue
- Hexachlorophene, Triclosan, Lysol, soap
www.freelivedoctor.com 7. Oxidizing Agents
- HOOH,hydrogen peroxide , is most common
- HOOH isnot a terribly effective disinfectantor anticeptic
- This is because bacteria and body tissues contain enzymes
(catalase) that inactivate hydrogen peroxide
- However, the oxygen released upon inactivation can help
oxygenate deep wounds and thus kill strict-anaerobe contaminants,
e.g.,Clostridium tetani
- Ozoneandperacetic acidare also oxidizing antimicrobial
agents
- They exert their effect by oxidizing cell macromolecules (e.g.,
proteins, DNA, etc.)
www.freelivedoctor.com 8. Glutaraldehyde Glutaraldehydeis
capable of effectiving sterilizationat room temperature,even
against endospores , and even in the presence of organics, but
achieving sterilization requriesmany hours of exposure and it
isnasty stuff to work with! www.freelivedoctor.com 9. Gaseous
Chemosterilizers
- Propylene oxide(C 3 H 6 O)
- Ethylene oxide(C 2 H 4 O)
- is used to sterilize heat- or moisture-sensitive items
- is used for items damaged by heat or moisture
- is not corrosive, not damaging to delicate instruments,
microscopes, disposable plastic instruments and materials
- permeates porous materials
- dissipates rapidly from material
- but is costly, toxic, carcinogenic, explosive, and relatively
lengthy process
www.freelivedoctor.com 10. Physical Antimicrobials
www.freelivedoctor.com Agent Mechanisms of Action Comments Moist
Heat, boiling Denatures proteins Kills vegetative bacterial cells
and viruses Endospores survive Moist Heat, Autoclaving Denatures
proteins 121C at 15 p.s.i. for 30 mink ills everything Moist Heat,
Pasteurization Denatures proteins Kills pathogens in food products
Dry Heat, Flaming Incineration of contaminants Used for inoculating
loop Dry Heat, Hot air oven Oxidation&Denatures proteins 170C
for 2 hours ;Used for glassware & instrument sterilization
Filtration Separation of bacteria from liquid (HEPA: from air) Used
for heat sensitive liquids Cold, Lyophilization (also desiccation)
Desiccation and low temperature Used for food & drug
preservation; Does not necessarily kill so used for Long-term
storage of bacterial cultures Cold, Refrigeration Decreased
chemical reaction rate Bacteriostatic Osmotic Pressure, Addition of
salt or sugar Plasmolysis of contaminants Used in food preservation
(less effective against fungi) Radiation, UV DNA damage (thymine
dimers) Limited penetration Radiation, X-rays DNA damage Used for
sterilizing medical supplies Strong vis. Light Line-drying laundry
11. Application of Heat
- Heat is frequently used to kill microorganisms
- Thermal death point(TDP) is the lowest temperature at which all
bacteria in a liquid culture will be killed in 10 minutes
- Thermal death time(TDT) is the length of time required to kill
all bacteria in a liquid culture at a given temperature
- Decimal reduction time(DRT) is the length of time in which 90%
of a bacterial population will be killed at a given temperature
(especially useful in canning industry)
- Dry heatkills by oxidation (slow, uneven penetration)
- Moist heatkills by protein coagulation (denaturation) so
requires lower temperatures or shorter times, but the moisture must
penetrate to pathogens to be effective (grease & oil can
block)
www.freelivedoctor.com 12. Moist Heat
- Moist heatkills microbes by denaturing enzymes (coagulation of
proteins)
- Boiling(at 100C, I.e., at sea level) kills many vegetative
cells and viruses within 10 minutes
- Autoclaving:steam applied under pressure (121C for 15 min) is
the most effective method of moist heat sterilizationthe steam must
directly contact the material to be sterilized
- Pasteurization:destroys pathogens( Mycobacterium tuberculosis
,Salmonella typhi , etc.)without altering the flavor of the
fooddoes not sterilize (63C for 30 seconds)
- Higher temperature short time pasteurization applies higher
heat for a much shorter time (72C for 15 seconds)
- An ultra-high-temperature, very short duration treatment (140C
for 3 sec.) is used to sterilize dairy products
www.freelivedoctor.com 13. Sterilization Times
- 171 oC, 60 minutes, dry heat
- 160 oC, 120 minutes, dry heat
- 149 oC, 150 minutes, dry heat
- 141 oC, 180 minutes, dry heat
- 121 oC, 12 hours, dry heat
- 121 oC, 15 minutes, moist heat (but dont start the clock until
entire item is up to tempe.g., large volumes fluid)
www.freelivedoctor.com 14. Evaluating Disinfectants
- compares efficacy to that of phenol, with greater efficacy
indicated with coefficient >1
- Salmonella typhiandStaphylococcus aureuscommonly used to
determine coefficients
- Filter-Paper/Disk Diffusion method
- placement of disinfectant impregnated filter paper on
well-inocated agar
- drying bacteria to surface followed by exposure to disinfectant
and subsequent washing and inoculation of sterile broth
www.freelivedoctor.com 15. Disk Diffusion Method
www.freelivedoctor.com Hypochlorous acid Phenol Lysol Nisin
Escherichia coli 16. Hands Spread Disease www.freelivedoctor.com
17. Link to Next Presentation www.freelivedoctor.com 18.
Acknowledgements http://www.sw.vccs.edu/rth/RTH_132/decont.ppt
http://www.nt.gov.au/powerwater/html/pdf/tennant_creek_chlorination.ppt
http://www.bugcruncher.com/ws/docs/lekcii/D&S_INQUAL_eng.ppt(nice
overview of specific antimicrobials)
http://www.delmarhealthcare.com/olcs/white/ppts/chapter%2021.ppt(nice
overview of microbilogy in nursing)
http://www.countyofkings.com/health/ehs/forms/FDHNDLR.ppt
http://bioeng.ttu.edu.tw/~chunyi/microbes/Chapter7.ppt
http://microbiology.okstate.edu/courses/micro2124/babus/Chpt7_files/chapter7.ppt
www.freelivedoctor.com 19. Chemical Antimicrobials * Type of
Disinfectant: H = High level; I = Intermediate level; L = Low level
www.freelivedoctor.com