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

Stable

Easy to work with

Otherwise not unpleasant

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)

Chlorine gas(Cl 2 )

Chlorine dioxide(ClO 2 )

Ozone(O 3 )

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

Phenol Coefficient

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

Use-Dilution test

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