Chapter 5 - Control of Microbial Growth Flashcards
Who introduced methods to prevent infection of wounds?
Lister
What are the 6 approaches to control?
- Sterilization
- Disinfection
- Pasteurization
- Decontamination
- Sanitization
- Preservation
What does sterilization do?
the sterile item is free of microbes but does not consider prions
What the two categories of Disinfection?
- disinfectants
2. antiseptics
What is pasteurization?
Brief heating to reduce number of spoilage organisms, destroys pathogens (not endospores)
–FOOD
What is preservation?
process of delaying spoilage of foods and other perishable products by adjusting the conditions and adding bacteriostatic (growth inhibiting) preservatives
What is special about protozoan cysts and oocysts?
They are resistant to disinfectants, excreted in feces, and cause diarrheal disease if ingested
What is special about the Pseudomonas species?
it is resistant to and can grow in some disinfectants
What is the D value?
The time required to kill 90% of population under specific conditions
What environmental conditions effect antimicrobials?
- Dirt, grease, body fluids can interfere with heat penetration and the action of some chemicals
- pH, temperature can influence effectiveness
- -low pH more effective
What are Critical items?
- items that come in direct contact with body tissues
- -must be sterile
- -needles and scalpels
What are semicritical instruments?
- items that come in contact with mucous membranes but do not penetrate body tissues
- -must be free of viruses and vegetative bacteria
- -includes endoscopes and endotracheal tubes
What are non-critical instruments?
- items that contact unbroken skin only
- -low risk of transmission
- -countertops, stethoscopes, blood pressure cuffs
What is innapropriate for use on plastic and other sensitive items?
- heat
- irradiation damages some types of plastic
What cannot be used to treat moisture sensitive material?
moist heat
What are the 5 methods of physical microbial control?
- Moist heat-denatures proteins
- Dry heat
- Filtration
- Radiation
- High pressure
What are 3 methods of Moist heat control?
- Boiling
- Pasteurization
- Autoclaving (pressurized steam)
What does boiling do?
boiling for 5 minutes destroys most microorganisms and viruses but not endospores
-DOES NOT STERILIZE
What does pasteurization do?
decreases the number of heat-sensitive microorganisms including spoilage microbes and pathogens (except sporeformers)
-DOES NOT STERILIZE
What does autoclaving do?
121˚C at 15psi for 15 minutes destroys endospores
- STERILIZES
- canning destroys clostridium botulinum endospores
What are 2 methods of Dry heat control?
- Incineration
- Dry heat ovens
- 200˚C for 90 minutes
What does incineration do?
burns cell components to ash
- flaming loop
- STERILIZES
What do dry heat ovens do?
destroys cell components and denatures proteins
- less efficient than moist heat and requires longer times and higher temps
- oxidizes cell components
What are the two forms of filtration and what does each do?
Fluids- various pore sizes remove bacteria
Air - HEPA filters remove organisms that have diameter of 0.3um or greater
What are the two types of radiation?
- Ionizing
2. UV radiation
What does ionizing radiation do?
destroys DNA and possibly damages cytoplasmic membranes
- produces reactive molecules that damage other cell components and can sterilize items after packaging
- Gamma and x-ray
- STERILIZES
What does UV radiation do?
Damages DNA
- penetrates poorly
- -used for air and drinking water; surfaces
- DOES NOT STERILIZE
- microwaves kill by heating but not directly, unevenly
What does high pressure do?
Treatments of 130,000 psi denature proteins and alter permeability of cell
- products retain color and flavor
- DOES NOT STERILIZE
What are alcohols and what are they used for?
- Ususlly 60%-80% aqueous solutions of ethyl or isopropyl alcohol
- kill vegetative bacteria and fungi
- not reliable against endospores and naked viruses
- used as antiseptic and disinfectant
- evaporates quickly limiting contact time and pure alcohol not effective
What are aldehydes and what are they used for?
- Glutaraldehyde and formaldehyde
- 2% alkaline glutaraldehyde common sterilant
- -immersion for 10-12 hrs kills all microbial life
- Formaldehyde used as a gas or as formalin (37% solution)
- -effective germicide that kills most microbes quickly
What are Biguanides and what are they used for?
- Chlorhexidine most effective
- used as antiseptics
- stays on skin, mucous membranes
- common in skin cream, mouthwash
What is Ethylene oxide gas used for?
- Useful gaseous sterilant
- destroys all microbes including endospores and viruses
- -STERILIZATION
- useful in sterilizing heat or moisture-sensitive items
- sterilizes disposable lab items
- -petri dishes, pipettes, equipment, implantable devices (pacemakers), artificial hips
What are metal compounds and what are they used for?
- high concentrations too toxic to be used medically
- Silver still used as disinfectant in creams or bandages
- compounds of mercury, tin, copper, and others once widely used as preservatives
What are halogens and what are they used for?
- Chlorine
- used as disinfectant but is caustic to skin and mucous membranes
- 1:100 dilution of household bleach effective
- presence of organic compounds is a problem - Iodine
- used as a disinfectant or antiseptic
- unreliable on endospores
- commonly used as iodophore
- -iodine slowly released from carrier molecule
What are peroxygens and what are they used for?
- powerful oxidizers used as sterilants
- Hydrogen peroxide effectiveness depends on surface
- -less effective as antiseptic; aerobic bacteria produce enzyme catalase
- –breaks down H2O2 to O2 and H2O
- -more effective as disinfectant on inanimate objects
- -vapor phase can be used as sterilant
- -less effective as antiseptic; aerobic bacteria produce enzyme catalase
- Peracetic acid is more potent than H2O2
- effective on organic material
- useful on wide range of material
What are Phenolic compounds (phenolics) and what are they used for?
- Phenol, one of the earliest disinfectants
- wide activity range, reasonable cost, remain effective in presence of detergents and organic matter
- some sufficiently non-toxic and used in soaps and lotions
- TRICLOSAN
What are Quaternary Ammonium Compounds and what are they used for? (Quats)
- cationic (+ charged) detergents
- nontoxic, used to disinfect food preparation surfaces
What are Chemical preservatives?
- weak organic acids (benzoic, sorbic, propionic)
- control molds and bacteria in foods and cosmetics
- Nitrate and nitrite used in processed meats
- -inhibit endospore germination and vegetative cell growth
- -higher concentrations give meats pink color
What does low temperature storage do?
- Refrigeration inhibits (DOESNT KILL) growth of pathogens and spoilage organisms by slowing or stopping enzyme reactions
- -psychrotrophs and psychrophilic organisms can still grow
- freezing preserves by stopping all microbial growth
What does reducing available water do?
- Inhibits microbes without killing them
- Accomplished by salting or adding sugar
- -increases environmental solutes
- -causes cellular plasmolysis (water exits bacterial cells)
- Lyophilization (freeze drying) foods is the application of low temperature and drying
- -used in coffee, milk, meats, fruits, vegetables
- Drying stops microbial growth but does not reliably kill
- -numerous cases of salmonellosis from dried eggs
