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Micro
Control of Microbial Growth
| Question | Answer |
|---|---|
| early civilizations used what methods to prevent microbial growth | salting, smoking, pickling, exposure of food and clothing to sunlight, and adding spices |
| prior to aseptic techniques, what percentage of surgeries and deliveries resulted in death due to nosocomial infection | 10 % and 25 % respectively |
| aseptic techniques were developed when by whom? | 1800s by Semmelweis and Lister |
| sterilization | killing or removing all forms of microbial life (including endospores) in a material or an object |
| commercial sterilization | heat treatment that kills endospores of Clostridium botulinum - does not kill thermophiles [not pathogenic] |
| disinfection | reducing the number of pathogenic microorganisms to the point where they no longer cause diseases (removal of vegetative or non-endospore forming pathogens) |
| four types of disinfection | disinfectant, antiseptic, degerming, and sanitization |
| disinfectant | applied to inanimate objects |
| antiseptic | applied to living tissue |
| degerming | mechanical removal of most microbes in a limited area (i.e. alcohol on the skin) |
| sanitization | use of chemical agent on food-handling equipment to meet public health standards and minimize chances of disease transmission (i.e. hot soap and water) |
| sepsis | (greek: putrid or decay), indicates bacterial contamination |
| asepsis | absence of significant contamination |
| aseptic techniques | used to prevent contamination of surgical instruments, medical personnel, and the patient during surgery (used to prevent bacterial contamination in the food industry |
| bacteriostatic agent | agent that inhibits the growth of bacteria, but does not necessarily kill them |
| germicide | an agent that kills certain microorganisms |
| four types of germicide | bactericide, viricide, fungicide, and sporicide |
| bactericide | an agent that kills bacteria, but does not kill endospores |
| viricide | an agent that inactivates viruses |
| fungicide | an agent that kills fungi |
| sporicide | an agent that kills bacterial endospores of fungal spores |
| factors that influence the effectiveness of antimicrobial treatment | number of microbes, type of microbes, environmental influences, and time of exposure |
| heat as an antimicrobial | kills microorganisms by denaturing their enzymes and other proteins |
| thermal death point (TDP) | lowest temperature at which all of the microbes in a liquid suspension will be killed in ten minutes |
| thermal death time (TDT) | minimal length of time in which all bacteria will be killed at a given temperature |
| decimal reduction time (DRT) | time in minutes at which 90% of bacteria at a given temperature will be killed (used in canning) |
| moist heat as an antimicrobial | kills microorganisms by coagulating their proteins (usu. more effective than dry heat), but requires temperatures above that of boiling water to be reliable |
| boiling | kills vegetative forms of bacterial pathogens, almost all viruses, & fungi & their spores w/in 10 minutes or less, but endospores & some viruses are not destroyed (i.e. hepatitis virus can survive 30 minutes & endospores can survive 20 hours of boiling) |
| autoclave | chamber which is filled with hot steam under pressure (temp. reaches 121 at 2 x atm. pressure) - all organisms and endospores killed within 15 minutes (not good for material that is heat, moisture, or high pressure damaged) |
| Pasteurization | developed by Louis Pasteur to prevent the spoilage of beverages (reduces microbes responsible for beer, milk, wine, and juice spoilage) |
| Classic Method of Pasteurization | milk was exposed to 65 C for 30 minutes |
| High Temperature Short Time Pasteurization (HTST) | (used today) milk is exposed to 72 C for 15 seconds |
| Ultra High Temperature Pasteurization (UHT) | milk is treated at 140 C for 3 seconds and then cooled very quickly in a vacuum chamber (milk can be stored at room temperature for several months) |
| dry heat | kills by oxidation effects |
| direct flaming | used to sterilize inoculating loops and needles - heat metal until it has a red glow |
| incineration | effective way to sterilize disposable items (paper cups, dressings) and biological waste |
| hot air sterilization | place objects in an oven (requires 2 hours at 170 C for sterilization since dry heat transfers heat less effectively to a cool body than moist heat) |
| filtration | removal of microbes by passage of a liquid or gas through a screen-like material with small pores, used to sterilize heat sensitive materials like vaccines, enzymes, antibiotics, and some culture media |
| High Efficiency Particulate Air Filters (HEPA) | used in operating rooms and burn units to remove bacteria from air |
| Membrane filters | uniform pore size, used in industry and research |
| membrane filters come in different sizes... | 0.22 and 0.45 micrometer pores and 0.01 micrometer pores |
| 0.22 and 0.45 micrometer pores | used to filter most bacteria, but don't retain spirochetes, mycoplasmas and viruses |
| 0.01 micrometer pores | retain all viruses and some large proteins |
| low temperature as an antimicrobial | effect depends on microbe and treatment applied |
| refrigeration | temperatures from 0 to 7 C have a bacteriostatic effect |
| bacteriostatic effect | reduces metabolic rate of most microbes so they cannot reproduce or produce toxins |
| freezing | temperatures below 0 C |
| flash freezing | does not kill most microbes |
| slow freezing | more harmful because ice crystals disrupt cell structure (over 1/3 of vegetative bacteria may survive 1 year, and most parasites are killed by a few days of freezing) |
| dessication | in the absence of water, microbes cannot grow or reproduce, but some may remain viable for year and grow again when water becomes available |
| Neisseria gonnorrhea | can only survive one hour without water |
| Mycobacterium tuberculosis | may survive several months without water |
| Clostridium spp. and Bacillus spp. | may survive decades without water |
| osmotic pressure | the use of high concentrations of salts and sugars in foods is used to create a hypertonic environment |
| plasmolysis | as water leaves the cell, the plasma membrane shrinks away from the cell wall causing the cell to die or stop growing |
| yeasts and molds | more resistant to high osmotic pressures |
| Staphylococci spp. | live on skin and are fairly resistant to high osmotic pressure |
| three types of radiation kill microbes | ionizing, ultraviolet, and microwave |
| ionizing radiation | gamma rays, X rays, electron beams, or higher energy rays that have short wavelenths (less than 1 nanometer) and dislodge electrons from atoms to form ions that cause DNA mutations and produce peroxides |
| ionizing radiation uses | sterilize pharmaceuticals and disposable medical supplies + food industry |
| disadvantages of ionizing radiation | penetrates human tissues and may cause genetic mutations in humans |
| ultraviolet light (nonionizing radiation) | wavelength is longer than 1 nanometer and damages DNA by producing thymine dimers which produce mutations |
| uses of ultraviolet light | disinfect operating rooms, nurseries and cafeterias |
| disadvantages of ultraviolet light | damages skin and eyes and doesn't penetrate paper, glass, and cloth |
| microwave radiation | wavelength ranges from 1 millimeter to 1 meter and causes heat to be absorbed by water molecules which may kill vegetative cells in moist foods |
| disadvantages of microwave radiation | bacterial endospores, which do not contain water, are not damaged by microwave radiation |
| Types of disinfectants | phenols and phenolics, halogens, alcohols, heavy metals, quaternary ammonium compounds (Quats), aldehydes, gaseous sterilizers, and peroxygens |
| phenol | (i.e. carbolic acid), acts as a local anesthetic and may be rarely used in some throat spray and lozenges (has a strong odor and is a skin irritant) |
| phenolics | chemical derivatives of phenol (i.e. cresols - derived from coal tar... lysol and biphenols - pHisoHex... effect against gram-positive staphylococci and streptococci, used in nurseries, but overuse may cause neurological damage |
| how phenols and phenolics act | destroy plasma membranes and denature proteins |
| advantages of phenols and phenolics | stable, persist for a long time after applied, and remain active in the presence of organic compounds |
| halogens are effective... | alone or in compounds |
| halogen - iodine | tincture of iodine (alcohol solution) - one of the first antiseptics and it combines with amino acid tyrosine in proteins and denatures proteins, but it can stain skin and clothes and be somewhat irritating |
| halogen - iodophors | compounds with iodine that are slow releasing, taking several minutes to act, and are used as skin antiseptic in surgery, but are not effective against bacterial endospores (betadine and isodine) |
| halogen - chlorine | forms hypochlorous acid when mixed w/ water and used to disinfect drinking water, pools, and sewage (organic materials easily inactivate) (i.e. sodium hypochlorite - in bleach and chloramine - chlorine & ammonia - less effective germicides) |
| alcohols | kill bacteria, fungi, not endospores or naked viruses, denature proteins & disrupt cell membranes, evaporate, leaving no residue, used to mechanically wipe microbes off skin b/4 injections/ blood draws, cause proteins to coagulate (bad for open wounds) |
| examples of alcohols | ethanol (drinking alcohol... optimum concentration is 70%) and isopropanol (rubbing alcohol - better disinfectant than ethanol, cheaper, and less volatile) |
| heavy metals | i.e. copper, selenium, mercury, silver, and zinc and work in tiny amounts |
| oligodynamic action | very tiny amounts are effective |
| silver | 1% silver nitrate used to protect infants against gonorrheal eye infections until recently |
| mercury | organic mercury compounds like merthiolate and mercurochrome are used to disinfect skin wounds |
| copper | copper sulfate is used to kill algae in pools and fish tanks |
| selenium | kills fungi and their spores and used for fungal infections (also used in dandruff shampoos) |
| zinc | zinc chloride is used in mouthwashes, zinc oxide is used as antifungal agent in paints |
| quaternary ammonium compounds (quats) | widely used surface active agents, cationic (+ changed) detergents, and are effective against gram positive bacteria, fungi, amoeba, & enveloped viruses, but less effective against gram-negative bacteria (i.e. zephiran [cepacol] - in lab spray bottles) |
| advantages of quats | strong microbial action, colorless, odorless, tasteless, stable, and nontoxic |
| disadvantages | form foam, organic matter interferes with effectiveness, and neutralized by soaps and anionic detergents |
| aldehydes | include some of the most effective antimicrobials, inactivate proteins by forming covalent crosslinks with several functional groups |
| formaldehyde gas as an aldehyde | excellent disinfectant, commonly used as formalin, a 37% aqueous solution (used to preserve biological specimens and inactivate viruses and bacteria in vaccines), but irritates mucous membranes (strong odor) (also used in mortuaries for embalming) |
| glutaraldehyde as an aldehyde | less irritating & more effective than formaldehyde, is a sterilizing agent (a 2$ solution of glutaraldehyde (Cidex) is bactericidal, tuberculocidal, and viricidal in 10 minutes, sporicidal in 3 to 10 hours), used to disinfect hospitals and for embalming |
| gaseous sterilizers | chemicals that sterilize in a chamber similar to an autoclave and denature proteins by replacing functional groups with alkyl groups |
| ethylene oxide as a gaseous sterilizer | kills all microbes and endospores, but requires exposure of 4 to 18 hours, toxic and explosive in pure form, highly penetrating, and most hospitals have ethylene oxide chambers to sterilize matresses and large equipment |
| peroxygen (oxidizing agents) | oxidize cellular components of treated microbes and disrupt membranes and proteins |
| ozone as a peroxygen | used along with chlorine to disinfect water, helps neutralize unpleasant tastes and odors, more effective killing agent than chlorine, but less stable and more expensive, highly reactive form of oxygen, and made by exposing oxygen to electricity/ UV light |
| hydrogen peroxide as a peroxygen | used as an antiseptic, not good for open wounds because quickly broken down by catalase present in human cells, effective in disinfection of inanimate objects, sporicidal at higher temps, and used by food industry and to disinfect contact lenses |
| benzoyl peroxide as a peroxygen | used in acne medication |
| peracetic acid as a peroxygen | one of the most effective liquid sporicides available (sterilant - kills bacteria and fungi in less than 5 minutes and kills endospores and viruses within 30 minutes) |
| peracetic acid uses | used widely in disinfection of food and medical instruments because it does not leave toxid residues |
Created by:
Nicolekr
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