Exam 3 Micro Lecture: Ch 7 Microbial Control
___________ is rapidly becoming the most popular team in the hospital. Who does it include?
Infection control team
Pharmacists all the way down to housekeeping
acquired in the hospital
What is the worst method for washing one’s hands?
Waterless, alcohol based hand wipes
The alcohol in the hand wipes dries out fast and you need a 70% alcohol solution to disinfect things so they do not work well and people do not really rub with friction to get stuff off with those.
What actually removes the bacteria while washing your hands?
The friction of you moving your hands back and forth.
The destruction or removal of all microbial life, including endospores.
Any treatment used on inanimate objects to kill or inhibit the growth of microorganisms; removing pathogens. Doesn't kill spores.
The removal of microorganisms from eating utensils and food preparation areas.
to make (an object or area) safe for unprotected personnel by removing, neutralizing, or destroying any harmful substance, as radioactive material or poisonous gas
We wish to control microbes under these two conditions
1. Destroy and reduce the transmission of pathogens
2. Reduce or eliminate contaminating microbes from food, water, special areas, etc.
the removal of microorganisms from an area
infected with a toxic or pathogenic organism in the blood or tissue, especially in respiratory or urinary tracts
free from pathogenic organisms (especially on skin) that cause disease or infection
free from contamination
2 main chemical disinfecting agents that kill microorganisms or inhibit their growth
1. - cides
2. - static
agents which kill microbes
Stops microbes from growing but do not kill them. The microbes are there and if you take the treatment away, they can resume growth.
kill microorganisms and viruses, but not necessarily endospores
Alcohol kills microbes best at what %?
protective structure to endure environmental stress
Most resistant organism to being killed
Microbes are considered to be dead when ______
they are unable to reproduce in conditions that normally support their reproduction
How do microbes die?
When you spray down a counter top, they're not all killed immediately.
Adding disinfectant in stationary phase makes death phase start the exponential decrease. This decrease will differ depending on the microbe.
When a population has been greatly reduced, the rate of death may slow due to survival of resistant organisms.
The population will be reduced by the same fraction in each time interval
Decimal reduction value. Also called D process.
Time required to kill 90% of the microbial population under specific conditions at that particular dose.
the dose of the disinfectant and how long you have to expose it for your # of microbes to be reduced by a power of 10.
1 D-process reduces the number of microbes by ______
Where you set up microbes in liquid culture and add to that culture different concentrations of your test disinfectant. Determine MIC or MBC.
Minimum inhibitory concentration. What is the minimum dose we need to have to prevent microbial growth> Doesn’t tell you one particular aspect: did we kill the microbes or did we just stop them from growing?
After MIC, the second step you can do as an add on is take the cultures that don’t look like they have microbes growing in them and dilute them into fresh media so its been diluted down to where the disinfectant is not going to work and we will see if the microbe grows back. Then we can determine the concentration we need to kill the microbes. Not just make sure it slows down and stops growing but gets killed.
how much can you dilute it?
5 disinfectant considerations
1. Dilution factor
2. Time of exposure
3. Target microbes
5. Surfaces of interest
Time of exposure
How long does it take for you to kill off the microbes? If you have to wipe down the counter for 30 minutes, its not useful.
Target of microbes
Making sure it kills the microbes you care about.
Surfaces of interest
Making sure it doesn’t degrade or have nasty effects on to whatever surface.
We use the size of that zone of inhibition to compare how effective different disinfectants are on killing any one microbe.
2 chemical control agents
2 gas control agents
3 liquid control agents
3 methods of mechanical control
3. filtration sterilization
2 types of filtration sterlization
2 physical control agents
2 types of radiation control agents
2. non ionizing
2 types of heat control
uses x-rays and gamma rays to sterilize
Destroys bacterial endospores
not always effective against viruses
How does ionizing radiation work?
strips electrons from atoms
Penetrates deep into objects
Causes damage to DNA and potentially to plasma membrane
Also indirect damage by producing reactive molecules
what two byproducts does ionizing radiation produce?
1. Superoxide free radicals
2. hydroxyl free radicals
uses UV rays to disinfect
Damages DNA causing thymine dimers
Generates free radicals
2 forms of dry heat control
2. dry oven
2 types of moist heat control
1. sterilization (steam under pressure)
2. disinfection (boiling water, hot water, pasteurization)
2 physical removal agents
2. soaps and detergents
breaks water surface tension
Emulsifies all hydrophobic lipids and fats so that you can physically remove the microbes from hands.
"savior of mothers"
The guy who figured out that washing hands is so important. Austrian surgeon in late 1800s. Delivered babies too. Before we had gloves they would go and do dissections of cadavers between giving birth. Friend of his got stuck with a scalpel and died and noticed that he died of what the pregnant women died of.
Figured out that if you wash your hands and instruments in a harsh chlorine bath (undiluted) then his patients survived. He became head of hospital and insisted everyone did this. Old surgical stink guys (see few slides later) did not like this and got offended by this saying I am a gentleman, I am clean. But he showed them the data.
He wore to surgery:
“an old blue frock-coat for operation, which he had previously worn in the dissecting room; stiff and glazed with blood”
Developed the first spray disinfectant: Carbolic Acid - phenol - will dissolve your skin. We do not use it anymore.
4 methods using heat and moisture
1. autoclave - true sterilization
Autoclave used to sterilize using pressurized steam
use saturated steam under pressure to reach temperatures above boiling
Autoclave achieves sterilization at ___°C and ___psi in ____minutes
What is it?
Does it sterilize?
What is it used for with our food?
Pasteur developed to avoid spoilage of wine
Controlled heating at temperatures well below boiling
Does not sterilize but significantly reduces organisms
Used to increase shelf life of food
What is it used for?
(High temperature short-term – HTST)
72°C for 15 seconds then rapid cooling (milk)
82°C for 20 seconds (ice cream)
ultra high temperature pasteurization
What is it used for?
140 to 150°C for 1 to 3 seconds
Used for single serving cream containers and boxed juices
The problem is that the higher the temp, the more likely you are to break down the chemical components of that food and alter the taste
Not as effective as moist heat
Sterilization requires longer times and higher temperatures
200°C for 1.5 hours vs. 121°C for 15 minutes
oxidizes cell constituents and denatures proteins
Oxidizes cell to ashes
Used to destroy medical waste and animal carcasses
Flaming laboratory inoculation loop incinerates organism
Energy released from waves
Shorter wavelength, higher frequency = more energy
Range of wavelengths is electromagnetic spectrum
Radiation can be ionizing or non-ionizing
Why is UV radiation limited to surface sterilization?
Limited to surface sterilization because UV radiation does not penetrate glass, dirt films, and other substances
99.9-99.99% effective against E. coli on leafy greens
Breaks down cell walls a bit though
Meats, poultry, some shellfish and spices are also approved
#1 way to sterilize plastics
ionizing radiation is used for sterilizing what?
Gamma radiation used for sterilization and pasteurization of antibiotics, hormones, sutures, plastic disposable supplies, and food
nonionizing radiation is used for what?
Used to destroy microbes in air, drinking water and surfaces
main sterilizing gas
How does sterilizing gas work?
Destroys microbes including endospores and viruses
Combines with and inactivates proteins
What is sterilizing gas used to sterilize?
Used to sterilize heat- or moisture- sensitive materials
what is the down side to using sterilizing gas?
Mutagenic and potentially carcinogenic
Extensive aeration of sterilized materials necessary
What are the vital targets for chemical microbial killing? (5)
1. Proteins (enzymes) - target its function, denature
2. Ribosomes - target its function
3. DNA - mutate it
4. Plasma membrane - poke holes in it, lysis
5. Cell wall - poke holes in it
3 main chemical methods of killing
1. disruption of plasma membrane
2. protein denaturation
First used by Lister ca. 1870
disruption of plasma membrane
How do phenols work?
Act by denaturing proteins and disrupting cell membranes
effective in presence of organic material and long lasting
Kill most vegetative cells (5-10% kill Mycobacterium)
Not reliable against all viruses
Things that poke holes in membranes and trigger cell lysis are things that contain phenol in them. Effective against most bacteria but not mycobacterium and spores. But lots of disinfectants have phenol type compounds in them. It can poke holes in plasma membranes and can poke holes in membranes of our cells.
Examples of phenols
4 main types of protein denaturation
3. heavy metals
4. quaternary ammonia
How does alcohol work as a chemical method of killing microbes?
Solutions of 60% - 80% isopropyl or ethyl alcohol kill vegetative bacteria and fungi. effective against mycobacteria.
Not effective against endospores and some naked viruses
Coagulates proteins and essential enzymes and damages lipid membranes
Commonly used as antiseptic and disinfectant
2 limitations to using alcohol as a chemical method of killing microbes
1. Evaporates quickly, limiting contact time
2. May damage material such as rubber and some plastics
How do heavy metals work as a chemical method of killing microbes?
e.g. Ions of mercury, silver, arsenic, zinc, and copper
Compounds combine with enzymes and proteins interfering with function
High concentrations of many metals toxic to human tissue
Silver still used as a disinfectant
Creams containing silver sulfadiazine used to prevent secondary infections
Also available on bandages for wound care
How does ammonia work as a chemical method of killing microbes?
It denatures proteins. Common in hospitals as detergent and denaturant. Pseudomonas bacteria causes infections in burn patients and in contact lens wearers. This bacteria has developed resistance against ammonia compounds.
2 main types of oxidation used in chemical microbial killing
1. halogens (iodine and chlorine)
2. hydrogen peroxide
How does hydrogen peroxide function as a chemical microbial killing agent?
Powerful oxidizing agent
Effectiveness depends on surface being treated
Living tissue produces catalase enzyme which breaks down hydrogen peroxide
More effective on inanimate objects
Useful as disinfectant
Leaves no residue
Doesn’t damage most materials
Hot solutions commonly used in food industry
Vapor-phase is more effective and can be used as sterilant
transfers electrons from one to another to break down physical components
How halogens work at killing microbes
Oxidize proteins and other cell components
How is iodine used as a chemical microbial killer?
Kills vegetative cells but not reliable with endospores
Used as a skin antiseptic in tincture or iodophore
effective with mycobacteria
How is chlorine used as a chemical microbial killer?
Works through oxidation
Used to disinfect water supplies and swimming pools, dairy and food industries
Effective household disinfectant
Caustic to skin and mucous membranes
Destroys vegetative bacteria and fungi, but not spores
Can react with organic matter to form carcinogenic compounds
8 points to consider in choosing a chemical microbial killer
1. Highly effective - Fast acting, even when dilute, have a broad range of activity over various environmental conditions, soluble and active in both water and oils
2. Activity in presence of organic material - Many germicides inactivated in presence of organic matter
4. Compatibility with material being treated - Liquids cannot be used on electrical equipment
5. Residue - Residues neither toxic or corrosive, odorless, non-staining
6. Cost and availability
8. Environmental risk