Lecture 11 and 12 Flashcards
Control of mircrobes in the environment 3
Control can mean
-killing of microbes on surface
-physical removal of microbes from a surface
-Preventing an increase in microbial number on a surface
(Control does not mean sterile environment)
Methods for controlling environmental microorganisms include: 2
- Physical Methods - heat, radiation, filtration
- Chemical Methods - antiseptics, disinfectants, preservatives
(they do not discriminate between types)
Heat
Denature proteins and DNA, melts lipids = cell death
- economical; easy to control and monitor
- moist heat is better than dry heat (faster penetration, better protein denaturation, water helps disrupt chemical bonds)
Boil water (heat control)
10 minutes at 100°C kills bacteria & viruses, but not spores (ie. boiling does not guarantee sterility)
Pressurized Steam (via autoclave)
20 min. of steam @ 15 lbs / inch (= 121°C) kills bacteria and spores (ie. proper autoclaving guarantees sterility)
How do you know if your stuff has been through an autoclave
Heat sensitive autoclave tape
Autoclave pouches with indicator strips
Good Habits to develop when working with sterilized materials
- check package integrity (rips, dmg)
- Check expiry date
- check indicator its been properly sterilized
- treat the inside of package as sterile, the outside not
Radiation
A) Ultraviolet Light
(germicidal lamps)
- Cross links bases in DNA (stops replication, causes mutations)
- 5 to 45 second exposure kills most microbes (depends on intensity)
But
-Not all types of microbes are equally sensitive (spore require more exposure times)
-dmg to skin eyes
-poor penetration of liquids, plastic glass
(for surface or air sterilization only! OR)
Radiation
B) Ionizing Radiation
- Dislodges electrons from atoms (disrupts chemical bonds, breaks DNA)
- Much higher penetrative power than UV
- Commercial uses only (cold sterilization)
- Sterilize heat-sensitive products; plastics; wrapped objects
- Food irradiation (to reduce bacterial numbers in foods)
Can a home microwave be used for sterilization
MW excite water molecules which release energy as heat
therefore killing of microbes is due to heat and needs water
Dry objects in a microwave will not sterilize it
Filtration
- Physical removal of microbes (no killing)
- Create filters with pores too small for (most) microbes to pass
membrane filters (cellulose fiber with pores 0.2 - 0.5 uM) (Bacteria, fungi trapped on surface of filter but viruses can pass)
For heat-sensitive liquids and gasses
- nutrients in bacterial growth media (vitamins)
- injectable drugs, surgical gasses
Chemical Methods
Germicides
Germicides
-Chemicals used to kill microbes on surfaces
Antiseptics - use on biological surface (skin)
Disinfectants - use on inanimate surfaces (non-living)
Chemical Methods
Preservatives
-Chemicals which may kill microbes, but usually only inhibit microbial by creating unfavorable environment
No selective toxicity
Overview - Germicidal
> 300 Chemicals that have anti-microbial properties
- > 8000 formulations
- different agents for different uses
Mechanism of action is usually by:
- Denaturing and coagulating cellular proteins
- Dissolving lipids (in cell membranes)
- Oxidizing cellular macro-molecules
Germicides are designed to:
- Greatly reduce the microbial “load” on a surface (always)
- create sterile surface (depends on agent)
Germicides - Factors affecting how well they work 5
Clean before disinfecting !!!
-Time of exposure (not all microbes killed at same rate)
-Temp of environment (less effective at lower temp)
-Concentration of germicide (higher is better, but more toxic)
-Presence of organic matter (soil, blood, pus form layer and weaken germicide)
-Number, type, and special characteristics of microbes present
(More germs more chemicals, spores hard to kill, biofilms resistant)
Germicides can be rated according to killing ability 2 level
Potency
choice of which
- High-level (sterilant) - kill all microbes, including spores
- Intermediate-level (everything except spores)
- Low-level (kills most vegetative bacteria but not mycobacteria, spores and some viruses)
-Potent germicides are also disinfectants
Choice of germicide depends on application and result
- biological vs inanimate surface
- complete sterility vs. only reducing microbial load
- risk category of device or surface being treated
Germicides - some examples relevant to health care
Phenols (Triclosan)
- earliest germicides (denatures proteins)[Lister/ carbolic acid used on skin]
- Skin irritation, neurotoxicity (absorbed through skin)
Used as disinfectant (Lysol = O-phenylphenol)
- high concentrations kill mycobacteria (not spores)
- Hexachlorophene (pHisoHex®) - use on newborns in early 70’s resulted in cases of brain damage
Small doses in medicine
Germicides - some examples relevant to health care
Phenols
Triclosan
- Chlorinated phenol with an unusual mode of action (stop an enzyme req. for bacterial fatty acid synthesis)
- Non irritating - used in consumer products (SUTURE THREAD, soap, toothpaste, deodorants, trash bags, utensils)
- Toxic concerns with long term exposure
Germicides - some examples relevant to health care
Alcohols (ethanol, isopropanol) 5
- Dissolves lipids and denatures proteins (effective against bacteria, viruses, fungi and not spores)
- Non-toxic and non irritating (antiseptic use)
- Mostly used as 70% solution in water (water aids protein denaturing and slows evaporation
- May not remove everything (deep in pores survive, and if bacteria present)
- Used as hand sanitation
Germicides - some examples relevant to health care
Peroxides-
Hydrogen peroxide (H2O2)
Accelerated Hydrogen Peroxide (PerCept)
Hydrogen peroxide (H2O2)
- Strong oxidizing agent breaks into water and oxygen killing anaerobic bacteria
- antiseptic, bedsores
contact lens solution
Accelerated Hydrogen Peroxide (PerCept)
- H2O2 + proprietary additives which give stability, and effectiveness
- used in hospitals to clean pt care areas
Germicides - some examples relevant to health care
Heavy Metals 5
Bind strongly to cellular proteins
- inactivates cellular enzymes and inhibits membrane functions
- antiseptic
Selenium -anti-fungal activity (topical creams)Silver sulfadiazine (burn wound ointment) Zinc compounds (mouthwashes, etc.)Thimerosal (mercury derivative) Copper
Germicides - some examples relevant to health care
Halogens (protein denaturation)
Chlorine
Iodine
Chlorine
- Bleach (javex) = sodium hypochlorite
- kills most microbes(and spores)
- inactivated by organic matter; poor long-term stability
Iodine
- less toxic and more stable than chlorine (antiseptic)
- Tincture (iodine plus alcohol)
- Iodophore (iodine + hydrocarbon carrier = carrier slows and prolongs iodine release)
eg. Betadine (Iodine + polyvinylpyrrolidone) = skin antiseptic
Germicides - some examples relevant to health care
Chlorhexidine
Disrupts membranes and denatures proteins
One of three antiseptics on WHO Essential medicines list
Low toxicity, none-irritable, sticks to skin and mucous membranes
- coating on catheters and implanted medical devices
- antiseptic skin creams and wipes (pre op skin care)
Germicides - some examples relevant to health care
Alkylating Agents
Glutaraldehyde
Ethylene Oxide, Propylene Oxide
Highly effective at denauting proteins nucleic acids
high level sterilant if given long exposure times (5-10 hours)
Glutaraldehyde
- Used in presence of organic material (medical/dental equipment/ tattoo parlors)
- Kills vegetative bacteria in 10 minutes and spores in 10 hours
Ethylene Oxide, Propylene Oxide
- Gaseous state lets penetration into hard to reach areas (equipment, implants, heat sensitive materials)
- Very toxic, explosive and carcinogenic (treated equipment must be flushed with sterile air before use)
When things go wrong
Outbreaks of hospital-acquired infections blamed on “failure” of a
germicide are instead usually due to:
- Not following procedures and manufactor instructions
- improper cleaning before use (not removing organic material)
- Using wrong agent for situation
“Soap, water, and common sense are yet the best antiseptics” William Osler (1849-1919)
Germicidal Chemicals in household (consumer products)
- contain chemical to make them antibacterial
- modest amounts
Concerns:
- resistance building
- removal of normal flora
Chemicals used as Preservatives 4
A product is microbiologically spoiled if:
- Microbes with pathogenic potential present
- Toxic microbial metabolites (eg LPS) present
- Microbial growth caused deterioration
Chemical can be added to products to prevent spoilage
- minimize risk of microbes introduced during making
- keep product safe after making
Chemicals sometimes kill microbes directly, but usually just alter environment so they cant grow (high acidity and low water activity)
Main requirement is that chemical be completely non toxic
“Aseptic” Techniques & Procedures
Practices & procedures to protect a patient from infection and prevent the spread of pathogenic microbes
Medical Asepsis (AKA CLEAN techniques) 5
- Reduce the number, or growth, or spread of germs on an object or environment
- Cleaning environment (disinfecting also)
- Proper handling and disposure of contaminated materials
- Handwashing
- Barrier precautions as needed (gloves)
Applied in all areas
Surgical Asepsis (AKA STERILE Techniques) 2
Eliminate all microbes and low risk of new ones
High risk areas
- Operatings rooms, labor and delivery
- Lab Diagnostic area (cariac cath lab)
- At Bedside in 3 main situations
1. Where skin is punctured
2. If skin is exposed because of burns/open wounds - Medical device inserted into sterile body
Setting up and working in a sterile field 5 steps
- Sterile touch sterile
- 1 inch from sterile is not sterile
- Arms and hands remains above waist and below shoulders
- If you cant see it, its not sterile so don’t turn your back
- Sterile field becomes contaminated as it is exposed to air (don’t talk or move)
Situational awareness” is key (ie. constantly be aware of your surroundings and think about what you’re doing)
