Disinfection and Sterilization PDF

Disinfection and Sterilization How to control microbes on objects.  What are we talking about: Decontamination, sanitizing – cleaning, rendering safe to handle - Usually required before disinfection/sterilization Disinfection – reduction in the number of microbes pre...

Disinfection and Sterilization How to control microbes on objects.  What are we talking about: Decontamination, sanitizing – cleaning, rendering safe to handle - Usually required before disinfection/sterilization Disinfection – reduction in the number of microbes present. – Differs in degree – “high level” destroys tough organisms (e.g. bacterial spores) Sterilization – elimination of all forms of life (except prions) – Absolute term; cannot be “partially sterile”.  Step 1: Decontamination /Sanitizing Cleaning to remove debris, blood , proteinaceous material and other soiling Reduces the burden of micro-organisms Reduces organic material that might interfere with subsequent disinfection or sterilization Allows the material to be handled safely if a disinfection step is incorporated into it.  Mode of Action of Disinfectants Disinfectants reduce numbers of organisms by the “microbial death rate” – Constant for the combination of circumstances – bug, agent, temperature – At low levels, residual bacteria may be inhibited rather than killed Mechanism of action may be by protein denaturation, or by membrane damage – Combination may occur with enzyme inactivation by other mechanisms Microbial Death Rate: Reduction in bacterial numbers is logarithmic and the proportion killed is constant for a particular set of conditions. (e.g. exposure to a concentration of a disinfectant) until low numbers are left. Note the line does not intersect the X axis Activity of Disinfectants: Denaturation of proteins results in loss of secondary and tertiary structure, with consequent loss of function. http://t2.gstatic.com/images?q=tbn:ANd9GcQXgePzUby  See full size image Disinfection Methods Disinfection using Chemicals. “Antiseptics” - disinfectants that can be used on skin ( e.g. alcohol, iodine). Disinfectant - usually used on inanimate objects. – May kill bacteria (bactericide) or prevent growth (bacteriostatic agent). See full size image Pasteurization (= moderate heat) Preservation File:Salt-packet.jpg – drying, osmotic methods, etc. – reduce numbers and prevent bacterial regrowth  Chemical Disinfection Factors important in disinfectant activity: – Disinfectant concentration – Time of exposure – Number and type of microbes present – Nature of material to be disinfected Mode of action – Disruption of cell membrane (e.g. detergents). – Denaturation of proteins (e.g. alcohol).  Low and Intermediate Level Disinfectants Defined by their spectrum of activity Low level will kill vegetative (=actively growing) bacteria, enveloped viruses, and some fungi – Often used for routine environmental and non critical equipment cleaning Intermediate will kill all bacterial pathogens except spores, most fungi, most viruses – Used for areas of high risk of contamination or on equipment coming into contact with mucous membranes  Examples of Disinfectants Phenol based - disrupt cell membranes and precipitate proteins. – As phenol is toxic, chemically altered (“substituted”) phenols – called ”phenolics”- are used. Alcohols - denature proteins. – Usually propanol, can be ethanol – 70% best, is more effective than 100% – Requires adequate time for activity  Oxidizing Disinfectants Halogens (fluorine, chlorine, iodine) - act by oxidation of enzymes. – 5.25% Hypochlorite (“javex”, household bleach) is commonly used. (It has 52,500 parts per million of chlorine). May be used diluted 1 in 10. – Used in water supplies (1-2 parts per million) – Often used for handling blood spills (no dilution) – Inactivated by organic material – Activity of preparations drops after opening – Danger of chlorine gas if acidified – Corrosive  Oxidizing disinfectants Hydrogen peroxides (H2O2) 0.5%-6% hydrogen peroxide for disinfection intermediate to high (high concentration) level disinfection. Some used as chemical sterilants – Used at 30% concentration as a sterilant Active in presence of organic matter Detergent properties improves cleaning ability Widely available; wipes or solution – These are now commonly used Higher concentrations can be corrosive, irritating, burn skin  Acid and Peroxides Hydrogen peroxide (H2O2) combined with acetic acid gives peracetic acid H2O2 combined with formic acid gives performic acid These are powerful disinfectants that are highly reactive: intermediate to high level Irritant Not affected by protein, or enzymes  “Quats” and Heavy Metals Quarternary ammonium compounds (“Quats”) – possibly disrupt membranes (these are low level disinfectants) – Have detergent activity – Commonly used for environmental cleaning Heavy metals. (e.g. copper, silver, lead) – May be incorporated into ointments, medical devices (e.g.urinary catheters) Antique copper water container  “High Level Disinfectants” Substances able to kill spores, tubercle bacilli, and viruses given enough time. – Examples Ortho-Phthalaldehyde Glutaraldehyde Formaldehyde (mixed with water gives formalin) Peracetic acid, performic acid Hydrogen peroxide With sufficient time of exposure and concentration, these agents become “chemical sterilants” Endoscope disinfection unit Glutaraldehyde  UV Disinfection UV light (wavelength 254 nm) is used Used for water, wastewater, air and surface disinfection. – Now used for terminal room disinfection in some hospitals. – Used in biological safety cabinets Can burn skin and damage vision with exposure to lamps. UV disinfecting Robot Times Colonist, Canadian Press  Antiseptics Disinfectants safe to use on skin Take time to work Resistance can develop to some of these. Include: – Alcohols – commonly used for skin disinfection – Iodophors – used for skin disinfection – Chlorhexidine - used for skin disinfection and handwashing – Triclosan – used for handwashing. (Often incorporated into soap)  Hand Disinfection Transient flora are organisms that are acquired on hands during routine work. It can include resistant organisms carried by patients and their environment These are easily transmitted to other patients who are debilitated or whose normal flora has been reduced As healthy individuals we are at a very low risk of becoming chronically colonized with these transient flora, but can carry them (carriage). Carriage can be eliminated by hand disinfection Handwashing -Semmelweiss Death rate in obstetrical ward was ~13% in 1847 Following a friend’s death, handwashing was introduced Death rate dropped to 2% Subsequently started to wash instruments in 1848 Death rate dropped to 0.85% in 1849 Colleagues rejected his findings and theories; death rate in 1860 was ~35% (he had left). Ignaz Semmelweiss 1818-1865  Hand Antisepsis & Alcohol Single most effective infection control practice Better than hand washing Use on clean dry hands Properly used = 99.9% bacterial kill Improves compliance with Routine Practices “Not to be used on wet or soiled hands”  Autoclave Sterilization Elimination of viable organisms. – (except prions, which are not generally expected to be present) Used for substances/devices to be inoculated into or to enter sterile sites of patients.  Methods Heat – moist (autoclaving) e.g. 121oC for 15 minutes – dry (oven, less effective) e.g. 350oF for 1 hour Gas and Liquid – ethylene oxide, aldehydes, – ozone, peracetic acid, H2O2 (oxidizing agents) Irradiation Filtration (does not eliminate viruses) A small filtration unit Filtration used for sterile solutions membrane  Autoclaving Moist heat (steam) at increased pressure for a defined time. – Commonly used in hospitals Can be used for most items (e.g. surgical instruments, fabrics, etc.). Ability to kill bacterial spores should be checked weekly. Autoclave Diagram  Double Door Autoclave Level 3 Lab Temperature vs Time An autoclave run.  Used for objects damaged by heat or radiation. Requires aeration step after sterilization Includes ethylene oxide, formaldehyde gas, hydrogen peroxide vapour, – plasma gas sterilization is a variant with production of reactive free radicals by radiation. Peracetic acid and glutaraldehyde are often referred to as “chemical sterilants” – Used in liquid phase Gas Sterilization  Plasma Plasma is ionized gas and very reactive.  Radiation Used in industry for plastic objects, fluids, etc. (not used much in hospitals) Uses microwave or gamma radiation UV destroys surface agents and is not a sterilizer – Often used in clinical situations for air, water or surface disinfection  cjdfoundation.org/about-cjd Prions Cause of Creutzfeldt-Jacob disease and “Mad Cow disease”. – Caused by transmissible misfolded proteins – No nucleic acid – Found in neurological tissue, e.g. brain Agents are resistant to disinfection/ sterilization with radiation or gas Incineration of surgical instruments: ideal Require alkaline conditions: soak in 1N NaOH + autoclaving