�Important words and concepts from Chapter 12, Black, 1999 (3/28/2003):
by Stephen T. Abedon (abedon.1@osu.edu) for Micro 509 at the Ohio State University
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Course-external links are in brackets
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Vocabulary words are found below
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(1) Chapter title: Sterilization and Disinfection
(a) Some general external links: [sterilization and disinfection (Google Search)]� [the control of microbial growth] [the control of microbial growth] [sterilization and disinfection (CDC hospital infections program)] [index]
(a) A disinfectant is a chemical or physical agent that is applied to inanimate objects to kill microbes
(b) [disinfectants (Google Search)] [index]
(a) Typically an antiseptic is a chemical agent that is applied to living tissue to kill microbes
(b) Note that not all disinfectants are antiseptics because an antiseptic additionally must not be so harsh that it damages living tissue
(c) With this constraint imposed on antiseptics, in general antiseptics are either not as cheap or not as effective at killing microbes as disinfectants
(d) [antiseptics (Google Search)] [antiseptic] [index]
(a) Sterilization is the killing of all microorganisms in a material or on the surface of an object
(b) A surface or an object is either sterile or it is not sterile, there are no gradations in sterility
(c) Typically the last things to die when one attempts sterilization is the highly heat- (and chemical-, etc.) resistant endospores
(d) [sterilization and microbiology (Google Search)] [index]
(a) Disinfection means reducing the number of viable microorganisms present in a sample
(b) Not all disinfectants are capable of sterilizing, but, of course, all disinfectants are employed with the hope of disinfecting
(c) [disinfection (Google Search)] [aircraft disinfection requirements] [child-care cleaning and disinfection] [Kleen� Pen pen and pencil disinfecting system] [index]
(a) Sanitization is the cleaning of pathogenic microorganisms from public eating utensils and objects such as that done by the kitchen of a restaurant
(b) [sanitization (Google Search)] [index]
(a) The killing of microorganisms occurs exponentially where some fraction of the living population dies per unit time
(b) "A definite proportion of the organisms die in a given time interval."
(c) "Soon the probability of finding even a single live organism becomes very small. Most laboratories say a sample is sterile if the probability is no greater than one chance in a million of finding a live organism."
(d) [exponential death (Google Search)] [index]
(a) "The fewer organisms present, the shorter the time needed to achieve sterility. Thoroughly cleaning objects before attempting to sterilize them is a practical application of this principle. Clearing objects of tissue debris and blood is also important because such organic matter impairs the effectiveness of many chemical agents."
(b) [cleanliness and disinfection (Google Search)] [index]
(a) "Microorganisms differ in their susceptibility to antimicrobial agents."
(b) Often what fails to be killed by a disinfectant are endospores though certain viruses and some vegetative bacteria are also highly resistant to disinfection
(c) Also, the same organism may differ in susceptibility depending on growth phase with actively growing organisms typically more susceptible to disinfection than not-growing cultures
(a) Increasing temperatures increases the efficacy of most chemical antimicrobials
(b) The converse of this statement is that relatively cold temperatures result in relatively poor disinfection
(c) [disinfection and temperature (Google Search)] [index]
(a) Generally, the use of more disinfectant provides better killing than the use of less disinfectant
(a) An antimicrobial that kills a microorganism (or, more specifically, a bacterium) is said to be bactericidal
(b) [bactericidal (Google Search)] [index]
(a) Some antimicrobials are only bacteriostatic, including some bactericidal agents used at too-low concentrations
(b) Bacteriostatic means that the antimicrobial inhibits bacterial growth but does not kill the bacteria; consequently, removal or dilution of the antimicrobial can result in a resurgence of bacterial growth
(c) Note that sufficient, prolonged application of even bacteriostatic agents can often result in bacterial death, a consequence, for example, of extended dormancy in which cellular repair is inhibited
(d) [bacteriostatic (Google Search)] [index]
(a) As quoted from your text: "An ideal disinfectant should
(i) Be fast acting even in the presence of organic substances, such as those in body fluid; [resistant to inactivation]
(ii) Be effective against all types of infectious agents without destroying tissues or acting as a poison if ingested; [broadly active]
(iii) Easily penetrate material to be disinfected without damaging or discoloring the material; [not poisonous or otherwise harmful]
(iv) Be easy to prepare and stable even when exposed to light, heat, or other environmental factors; [penetrating; not damaging to non-living materials]
(v) Be inexpensive and easy to obtain and use; [stable; easily prepared]
(vi) Not have an unpleasant odor. [not unpleasant to work with]"
(b) Note that different disinfectants typically have different strengths and weaknesses, and often what disinfectant one uses depends on circumstances
(c) Remember, the best thing one can do if unsure or ignorant of disinfectant abilities is to read the label
(d) [ideal disinfectant (Google Search)] [phenol factsheet] [index]
(15) Mechanisms of action of chemical agents
(a) Different disinfectants have different mechanisms of action
(b) All disinfectants act by harming microorganisms in some manner
(c) Mechanisms of harm include
(i) Protein denaturation
(ii) Membrane disruption
(iii) Nucleic acid damage
(iv) Inhibition of metabolism
(16) Specific antimicrobial agents
(a) A variety of chemical antimicrobials exist including
(i) Surfactants
(ii) Various organic acids and bases
(iii) Heavy metals
(iv) Halogen-containing compounds
(v) Alcohols
(vi) Phenol and phenol derivatives
(vii) Oxidizing agents
(viii) Alkylating agents
(ix) Certain dyes
(x) Other agents
(b) A variety of physical antimicrobials exist including
(i) Heat (the most economical and widely employed antimicrobial)
(iii) Ionizing radiation
(iv) Strong visible light
(v) Ultrasonic waves
(vi) Filtration
(vii) Osmotic pressure
(c) We additionally will consider freezing as a means of microbe preservation
(a) Surfactants are substances that are soluble in water but are able to dissolve lipids
(b) In that way they are able to increase the solubility of lipids in water solutions
(c) Surfactants additionally increase the ability to water solutions to wet, i.e., move along or penetrate, lipid surfaces
(d) Examples of surfactants are soaps and detergents
(e) [surfactants and disinfection (Google Search)] [index]
(a) Soaps are sodium or potassium salts of fatty acids
(b) Consequently, soaps are alkaline (pH greater than 7)
(c) Soaps exert their antimicrobial effects in two ways
(i) By harming bacteria that are sensitive to high pH's
(ii) By removing pathogens from surfaces by cleaning the surface (a.k.a., degerming)
(d) See Figure 12.3, The action of a surfactant [which shows, particularly, soaps in action]
(e) [soap and disinfection (Google Search)] [index]
(a) Detergents are synthetic surfactants
(b) There are a variety of structural types of detergents
(c) A detergent may be cationic (positively charged) or anionic (negatively charged)
(d) Cationic detergents are better at killing bacteria than anionic detergents
(e) [detergents and disinfection (Google Search)] [index]
(20) Quaternary ammonium compounds (quats)
(a) One type of commonly employed cationic detergent disinfectants are quaternary ammonium compounds (quats)
(b) Problems with the use of quats as disinfectants include
(i) Their inactivation by soaps
(ii) Their inhibition by divalent cations (calcium and magnesium ions)
(iii) Their inhibition by cotton and other porous organic substances
(iv) Their inability to kill certain species of Pseudomonas
(c) "Quats are now often mixed with another agent to overcome some of these problems and to increase their effectiveness."
(d) ["quarternary ammonium" and disinfection, quats and disinfection (Google Search)] [adding ammonia to their chlorine disinfection systems] [index]
(a) Various organic acids are employed especially as inhibitors of fungi and molds in foods
(b) For example, benzoate of soda is a sodium salt of benzoic acid, an organic acid
(c) [antimicrobial and "organic acids" (Google Search)] [index]
(a) Various metals and metal salts are commonly employed to prevent microbial growth or kill microbes
(b) For example, silver nitrate has been and increasingly is again used to treat the eyes of newborns to kill any Neisseria gonorrhea that may have been acquired during passage down the birth canal
(c) A common example in Ohio is the treatment of ponds with copper sulfate (which is blue in water solution) as an anti-algal; note that though effective at inhibiting algal growth in ponds, it may be similarly disruptive of algal growth in down-stream ecosystems
(d) Selenium compounds are effective antifungals
(e) ["silver nitrate" and antimicrobial (Google Search)] [index]
(a) Halogens are the seventh (VII) column of the periodic table of elements
(b) Two halogens are regularly employed as antimicrobials: iodine and chloride
(c) [halogens and disinfection (Google Search)] [index]
(24) Chlorine and Hypochlorite ion
(a) Drinking water is commonly disinfected using hypochlorite
(b) Hypochlorite may either be added directly (i.e., in the form of bleach) or created within water by bubbling chlorine gas through the water
(c) Note that chlorine is less effective in the presence of significant organic compounds (basically because the hypochlorite ion interacts with--oxidizes--organic compounds indiscriminately and thus is used up in the presence off excess organic compounds)
(d) (bromine sometimes is employed as a substitute for chlorine)
(e) [chlorine and disinfection, hypochlorite and disinfection (Google Search)] [index]
(a) Iodine is often employed as a tincture or as an iodophor
(b) A tincture is an alcohol solution of a substance, in this case iodine
(c) Iodine tinctures may be employed as antiseptics
(d) [iodine and disinfection (Google Search)] [index]
(a) Iodophors are organic compounds that slow the release of iodine
(b) The iodophors additionally serve as surfactants, thus increasing penetration while simultaneously steadily supplying iodine over long periods
(c) Betadine and Isodine are examples of iodophors
(d) [iodophor and disinfection, betadine and disinfection, isodine and disinfection (Google Search)] [index]
(a) Alcohols work best as 70 to 99% mixtures with water
(b) Alcohol-water mixtures are additionally more penetrating than pure alcohols
(c) Either ethanol or isopropyl (rubbing) alcohol may be employed for disinfecting
(d) Alcohols are especially appropriate for application to sites in which their propensity to evaporate away is convenient (e.g., to disinfect skin prior to injection)
(e) The down side of alcohols is that they are not terribly penetrating nor capable of killing endospores or other resistant cells
(f) Alcohols should not be applied to wounds since they can cause tissue damage
(g) [alcohol and disinfection (Google Search)] [index]
(28) Phenol and phenol derivatives (phenolics)
(a) Phenol and their derivatives (called phenolics) are especially useful when disinfecting materials contaminated with organic materials
(b) Lysol� employs phenolics
(c) Some phenolics are mild enough for use as antiseptics while others are too harsh or otherwise dangerous to be employed on living tissue
(d) [phenol and disinfection (Google Search)] [index]
(29) Oxidizing agents (hydrogen peroxide)
(a) Hydrogen peroxide (HOOH) is a typical oxidizing agent
(b) Note that hydrogen peroxide is actually not a terribly effective antiseptic or disinfectant
(c) This is because bacteria and body tissues contain enzymes (catalase) that inactivate hydrogen peroxide
(d) On the other hand, the oxygen released upon inactivation can help oxygenate deep wounds and thus kill strict-anaerobe contaminants
(e) [peroxide and disinfection (Google Search)] [index]
(30) Alkylating agents (formaldehyde, glutaraldehyde, ethylene oxide)
(a) Formaldehyde, glutaraldehyde, and ethylene oxides are alkylating agents�they add carbon-containing functional groups to biological molecules
(b) Formaldehyde is employed to inactivate viruses and toxins to produce whole-killed vaccines and toxoid vaccines [whole-killed vaccines]
(c) Glutaraldehyde is capable of sterilizing equipment, though to effect sterilization often requires many hours of exposure
(d) Ethylene oxide is a gaseous chemosterilizer that is especially useful due to its extraordinary penetrating power; this allows it to penetrate all sorts of nooks and crannies
(e) Ethylene oxide is employed to sterilize prepackaged laboratory equipment that is otherwise destroyed by heat (e.g., plastic petri dishes)
(f) [ethylene and disinfection (Google Search)] [ethyleneoxide second edition] [ethylene oxide laboratory safety] [ethylene oxide UATW] [index]
(g) [formaldehyde and disinfection, glutaraldehyde and disinfection (Google Search)] [index]
(a) Heat is a highly efficient means of sterilization so long as the material to be sterilized is resistant to heat
(b) Different types of heat application include
(i) Dry heat
(ii) Moist heat
(iii) Pasteurization
(c) [heat and disinfection (lots of stuff on disinfecting contact lenses), heat and disinfection -contact, heat and sterilization (Google Search)] [index]
(a) To effect sterilization dry heat typically requires higher temperatures than moist heat
(b) It also is less penetrating and requires longer exposure
(c) Nevertheless, application of dry heat is cheap and easy
(d) Typically one bakes materials in an oven at
(i) 171�C for at least one hour
(ii) 160�C for at least two hours
(iii) 121�C for at least 16 hours
(e) Note that the length of exposure necessary is inversely proportional to the temperature (lower temps require longer exposures)
(f) Note additionally that the times given are for once the indicated temperature has been achieved; this is true for all methods of disinfection and sterilization: the clock does not begin until the material has been exposed to the antimicrobial
(g) Incineration is another common method of dry heat sterilization, e.g., such as the flame incineration of an inoculating loop
(h) [disinfection and "dry heat" (Google Search)] [index]
(a) Moist heat is more effective than dry heat at a given temperature or length of exposure
(b) Moist heat is also more penetrating than dry heat
(c) However, to achieve sterilization employing moist heat requires rather elaborate equipment, i.e., the employment of an autoclave
(d) Just as with dry heat, temperature and length of exposure are inversely related and penetration is absolutely critical
(e) With moist heat, penetration is even more of a problem since penetration of heat without associated penetration of moisture is simply dry heat and dry heat is less effective as an antimicrobial than moist heat; consequently, things that block moisture penetration can inhibit sterilizing efficacy
(f) Boiling water is the most common form of application of moist heat but is not capable of killing endospores or killing all viruses
(g) [disinfection and "moist heat" (Google Search)] [index]
(a) An autoclave is a high pressure device used to allow the application of moist heat above the normal-atmosphere boiling point of water
(b) Exposure to 121�C for 15+ minutes is typically sufficient to sterilize
(c) Again, the material must be 121�C before the clock starts
(d) Large items, large volumes, and items that are poorly penetrated by steam may take much longer than 15 minutes to sterilize
(e) See Figure 12.10, The autoclave
(f) [autoclave (Google Search)] [index]
(a) Pasteurization is the application of moist heat of less-than boiling temperatures to foods to prevent the growth of food-spoiling organisms as well as various heat-labile pathogens
(b) [pasteurization (Google Search)] [index]
(a) Microbial preservation includes methods of avoiding all of the above as well as the ravages of exponential decline associated with the standard bacterial growth curve
(b) Methods of microbial preservation include:
(i) Refrigeration
(ii) Freezing
(iii) Desiccation
(iv) Freeze drying (lyophilization)
(c) [microbe preservation (Google Search)] [index]
(a) Refrigeration is a great short term solution, but it merely slows the decline of organisms rather than preventing it
(b) Of course, for psychrophiles the refrigerator could represent a fairly good growth environment
(c) [refrigeration and microbiology (Google Search)] [index]
(a) Freezing is employed to more completely stave off organismal deterioration
(b) For organisms that survive the freezing process, freezing constitutes a reasonably good long-term preservation method with prevention of deterioration increasing as temperatures are lowered
(c) Prevention of damage during freezing is accomplished by mixing cultures with glycerol
(d) Lower temperatures result in greater long-term storage:
(i) -20�C is the temperature of a standard freezer
(ii) -80�C is a good temperature for long-term storage of microorganisms
(iii) -180�C is the temperature of liquid nitrogen, a common medium for long-term storage of microorganisms
(e) [freezer and microbiology, freezing and microbiology (Google Search)] [index]
(a) Desiccation means drying, i.e., removal of water
(b) Desiccation prevents organism metabolism, and is a good means of preventing organism growth
(c) Desiccation is an effective means of organism storage for those organisms capable of remaining viable upon desiccation
(d) [desiccation and bacteria (Google Search)] [index]
(40) Freeze drying (lyophilization)
(a) Freeze-drying involves freezing something and then evacuating air so that boiling occurs at low temperatures; this desiccates material thereby preventing deterioration and spoilage
(b) Lyophilization is the word used for the freeze-drying preservation of microorganisms; it is widely effective but has been to a large extent supplanted by the use of ultra-low temperature freezers (e.g., -80�C)
(c) [lyophilization, preservation and bacteria and "freeze dry" (Google Search)] [index]
(41) Ultraviolet (UV) radiation
(a) UV light is not terribly penetrating but is good for disinfecting surfaces and air
(b) This is accomplished by a long-term exposure to UV light
(c) On the down side, UV light is damaging to human tissue as well as to many plastics
(d) [ultraviolet and disinfection (Google Search)] [UV waterworks: reliable, inexpensive water disinfection for the world] [safe sun?] [index]
(a) Ionizing radiation is radiation that ionizes water; this temporarily turns water into an oxidizing agent
(b) Different types of ionizing radiation display different degrees of penetration
(c) One potential application of ionizing radiation is as an antimicrobial is in food preservation
(d) [disinfection and "ionizing radiation" (Google Search)] [index]
(a) Strong visible light can negatively affect bacterial viability so excessive exposure to strong visible light should be avoided when one's goal is culture preservation
(b) Practical application of strong visible light to disinfection involves the use of sun light to dry laundry (i.e., that �old-fashioned� alternative to a cloths dryer)
(c) [bacteria and "strong visible light" (Google Search)] [solar disinfection studies: drinking water] [water disinfection by solar radiation] [index]
(44) Filtration (HEPA filters)
(a) Filtration is a common means of antimicrobial treatment used when materials are heat labile
(b) Filtration does not necessarily sterilize unless very small filter pores are employed (and the speed and ease with which one may filter something is indirectly proportional to pore size with large pores much quicker and easier than small pores)
(c) High-efficiency particulate air (HEPA) filters are used to filter the air flowing into aseptic environments and out of potentially contaminated ones (e.g., containment facilities)
(d) [filtration and microbiology, "hepa filter" -vacuum (Google Search)] [minimize microbial growth] [index]
(a) Lister's disinfectant, phenol, is considered the disinfectant standard against which all other disinfectants are compared
(b) These comparisons give rise to the phenol coefficient where a disinfectant that
(i) is more efficacious than phenol is given a phenol coefficient that is greater than 1
(ii) one less efficacious than phenol is given a coefficient of less than 1
(iii) one of equal efficacy to phenol is given a phenol coefficient of 1 (i.e., efficacy of disinfectant divided by efficacy of phenol)
(c) Two organisms, Salmonella typhi and Staphylococcus aureus are commonly used to determine phenol coefficients
(d) Note that phenol coefficients are determined under an "ideal" condition and therefore may not be indicative of disinfectant performance under other conditions
(e) See Table 12.2, Phenol coefficients of various chemical agents [to get a feel for relative efficacies as well as how phenol coefficients may be employed]
(f) [phenol coefficient (Google Search)] [phenol factsheet] [index]
(a) A method that requires less manipulation to judge the efficacy of disinfectants is the filter paper method
(b) Here filter paper is soaked with disinfectant and then simply placed on the agar surface of a petri dish that has been inoculated with a lawn of test organism
(c) The clear area around the disk following incubation is used as an indication of disinfectant efficacy
(d) Figure 12.1, The filter paper method of evaluating disinfectants and antiseptics
(e) [disinfection and "filter paper" (Google Search)] [index]
(a) A third method of determining disinfectant efficacy, and one that is especially useful for determining the ability of disinfectants to kill microorganisms dried onto a typical clinical surface (stainless steel) is the use-dilution test
(b) Organism is air dried onto a stainless-steel surface and then exposed to disinfectant; following sterile-water rinsing the entire surface is then placed in broth; successful disinfection results in no bacterial growth in the broth
(c) Disinfectants that completely kill (or otherwise remove) microbes at the lowest dilutions (of the disinfectant) are considered the most efficacious
(d) [use-dilution test (Google Search)] [index]
(48) Vocabulary [index]
(a) Alcohols
(c) Antiseptic
(d) Autoclave
(g) Chlorine
(j) Desiccation
(k) Detergent
(l) Disinfectant
(m) Disinfection
(n) Dry heat
(o) Ethylene oxide
(r) Filtration
(s) Formaldehyde
(t) Freeze drying
(u) Freezing
(v) Glutaraldehyde
(x) Heat
(y) Heavy metals
(z) HEPA filters
(aa) Hydrogen peroxide
(bb) Hypochlorite ion
(dd) Iodine
(ee) Iodophors
(ff) Ionizing radiation
(gg) Lyophilization
(hh) Mechanisms of action of chemical agents
(jj) Moist heat
(kk) Organic acids
(nn) Pasteurization
(oo) Phenol and phenol derivatives
(pp) Phenol coefficient
(qq) Phenolics
(rr) Refrigeration
(ss) Quaternary ammonium compounds
(tt) Quats
(uu) Sanitization
(vv) Soap
(ww) Specific antimicrobial agents
(xx) Sterilization
(yy) Strong visible light
(zz) Surfactants
(aaa) Temperature effects
(bbb) Ultraviolet (UV) radiation
(ccc) Use-dilution test
