Chp 7 Flashcards
Sepsis
refers to bacterial contamination
Asepsis
is the absence of significant contamination
Aseptic surgery techniques prevent
the microbial contamination of wounds
Sterilization
removing and destroying all microbial life
Commercial sterilization
killing C. botulinum endospores from canned goods
Disinfection:
destroying harmful microorganisms
Antisepsis:
destroying harmful microorganisms from living tissue
Degerming
the mechanical removal of microbes from a limited area
Sanitization
lowering microbial counts on eating utensils to safe levels
Biocide (germicide):
treatments that kill microbes
Bacteriostasis:
inhibiting, not killing, microbes
(rate of microbial death) Effectiveness of treatment depends on:
1) Number of microbes
2) Environment (organic matter, temperature, biofilms)
3) Time of exposure
4) Microbial characteristics
Actions of Microbial Control Agents
1) Alteration of membrane permeability
2) Damage to proteins (enzymes)
3) Damage to nucleic acids
Thermal death point (TDP):
lowest temperature at which all cells in a liquid culture are killed in 10 min
Thermal death time (TDT):
minimal time for all bacteria in a liquid culture to be killed at a particular temperature
what does heat do to enzymes
denatures
Decimal reduction time (DRT)
Minutes to kill 90% of a population at a given temperature
Moist Heat Sterilization
1) Moist heat denatures proteins
2) Boiling
3) Free-flowing steam
Autoclave
- steam under pressure
- 121 C at 15 psi for 15 min
- Kills all organisms and endospores
- Steam must contact the item’s surface
Moist Heat Sterilization
Large containers require longer sterilization times
Test strips are used to indicate sterility
Pasteurization
reduces spoilage organisms and pathogens
Thermoduric
organisms survive
Dry Heat Sterilization
Kills by oxidation
- Flaming
- Incineration
- Hot-air sterilization
Filtration is the
Passage of substance through a screenlike material
filtration is used for
heat-sensitive materials
Two types of filters
1) High-efficiency particulate air (HEPA) filters
- remove microbes > 0.3 µm
2) Membrane filters
- remove microbes > 0.22 µm
Physical Methods of Microbial Control
1) Low Temp
2) High Pressure
3) Desiccation
4) osmotic pressure
Low temp and microbial control
Low temperature has a bacteriostatic effect
Examples
- Refrigeration
- Deep-freezing
- Lyophilization (freeze drying)
High pressure and microbial control
denatures proteins
Desiccation and microbial control
absence of water prevents metabolism
Osmotic pressure and microbial control
Omotic pressure uses salts and sugars to create hypertonic environment; causes plasmolysis
Radiation types
Ionizing radiation
Non ionizing radiation
Microwaves
Ionizing radiation
(X rays, gamma rays, electron beams)
1) Ionizes water to create reactive hydroxyl radicals
2) Damages DNA by causing lethal mutations
Nonionizing radiation
(UV, 260 nm)
Damages DNA by creating thymine dimers
Microwaves
kill by heat; not especially antimicrobial
Principles of Effective Disinfection
1) Concentration of disinfectant
2) Organic matter
3) pH
4) Time
Dilution Tests
1) Metal cylinders are dipped in test bacteria and dried
2) Cylinders are placed in disinfectant for 10 min at 20°C
3) Cylinders are transferred to culture media to determine whether the bacteria survived treatment
The Disk-Diffusion Method
1) Evaluates efficacy of chemical agents
2) Filter paper disks are soaked in a chemical and placed on a culture
3) Look for zone of inhibition around disks
Phenol and Phenolics
Injure lipids of plasma membranes, causing leakage
Bisphenols
1) Contain two phenol groups connected by a bridge
2) Hexachlorophene and triclosan
3) Disrupt plasma membranes
Biguanides
1) Chlorhexidine
2) Used in surgical hand scrubs
3) Disrupt plasma membranes
Halogens
Iodine
Chlorine
Iodine
is a halogen
1) Tincture: solution in aqueous alcohol
2) Iodophor: combined with organic molecules
3) Impairs protein synthesis and alters membranes
Chlorine
is a halogen
1) Oxidizing agents; shut down cellular enzyme systems
2) Bleach: hypochlorous acid (HOCl)
3) Chloramine: chlorine + ammonia
Alcohols
1) Denature proteins and dissolves lipids
2) No effect on endospores and nonenveloped viruses
3) Ethanol and isopropanol
- Require water
Heavy Metals and Their Compounds
Oligodynamic action—very small amounts exert antimicrobial activity
Denature proteins
Ag, Hg, Cu, Zn
- Silver nitrate is used to prevent ophthalmia neonatorum
- Mercuric chloride prevents mildew in paint
- Copper sulfate is an algicide
- Zinc chloride is found in mouthwash
Chemical Food Preservatives
1) Sulfur dioxide prevents wine spoilage
2) Organic acids
- Inhibit metabolism
- Sorbic acid, benzoic acid, and calcium propionate prevent molds in acidic foods
3) Nitrites and nitrates prevent endospore germination
Antibiotics
Bacteriocins—proteins produced by one bacterium that inhibits another
Nisin and natamycin prevent spoilage of cheese
Aldehydes inactivate
proteins by cross-linking with functional groups
Aldehydes are used
for preserving specimens and in medical equipment
examples:
-Formaldehyde and ortho-phthalaldehyde
-Glutaraldehyde is one of the few liquid chemical sterilizing agents
Chemical Sterilization
1) Gaseous sterilants cause alkylation—replacing hydrogen atoms of a chemical group with a free radical
2) Cross-links nucleic acids and proteins
3) Used for heat-sensitive material
Ethylene oxide
Plasma
1) Fourth state of matter, consisting of electrically excited gas
2) Free radicals destroy microbes
3) Used for tubular instruments
Supercritical Fluids
1) CO2 with gaseous and liquid properties
2) Used for medical implants
Peroxygens and Other Forms of Oxygen
1) Oxidizing agents
2) Used for contaminated surfaces and food packaging
O3, H2O2, and peracetic acid
