Chapter 5 Control of MIcrobial Growth Flashcards
Joseph Lister
man who saved more lives by the introduction of his system than all the wars of the 19th century. Applied carbolic acid to wounds to prevent gangrene. sterilizing instruments, clean areas.
Sterile
a sterile item is one that is free of microbes, including endospores and viruses. (does not include prions)
Sterilization
removal or destruction of all microorganisms and viruses on a product
Disinfection
the elimination of most or all pathogens on a material. (some living microbes remain)
Disinfectants
antimicrobial chemicals used for disinfecting inanimate objects. they are toxic to many forms of life, and therefor biocides (bio means life and cida means to kill)
Germicides
chemicals that target microorganisms and viruses
Bactericidal
they kill bacteria
Antiseptics
antimicrobial chemicals non toxic enough to be used on skin or other body tissue. these are routinely used to decrease bacterial numbers on skin before invasive procedures such as surgery.
pasteurization
a brief heat treatment that reduces the number of spoilage organisms and destroys pathogens. foods and inanimate objects can be pasteurized.
decontamination
a process used to reduce the number of pathogens to a level considered safe to handle. the treatment can be as simple as thorough washing, or it may involve the use of heat or disinfectants
Sanitization
generally implies a process that substantially reduces the microbial population to meet accepted health standards. most people also expect a sanitized object to look clean. note that this term does not indicate any specific level of control
preservation
the prcoess of delaying spoilage of foods or other perishable products. one way to do this is to adjust storage conditions to slow microbial growth. alternatively, chemical preservatives can be added. (bacteriostatic)
bacteriostatic
chemical preservatives that inhibit growth of bacteria but do not kill them.
disinfection by-products (DBP)
compounds formed when chlorine or other disinfectants react with naturally occurring chemicals in water
certain pathogens, particularly, Cryptosporidium parvum, a cause of diarrhea, can survive traditional disinfection procedures. to address these problems, water treatment regulations now require facilities to minimize the level of both BDP’s and C. parvum in treatdd water.
Bacterial endospores
the endospores of Bacillus, Clostridium and related genera are the most resistant form of life typically encountered. only extreme heat or chemical treatment ensures their complete destruction.
Protozoan cysts and oocysts
cysts and oocysts are stages in the life ciycle of certain intestinal protozoan pathogens such as Giardia lamblia and Cryptosporidium parvum. these disinfectant-resistant forms are excreted in the feces of infected animals, including humans, and can cause diarrheal disease if ingested. Unlike endospores, they are easily destroyed by boiling.
Mycobacterium species
the waxy cell walls of mycobacteria make them resistant to many chemical treatments. because of this, stronger, more toxic chemicals must be used to disinfect environments that may contain Mycobacterium tuberculosis, the cause of tuberculosis.
Pseudomonas species.
these commonb environmental organisms are not only resistant to some disinfectants, but in some cases actually grown in them. Pseudomonas species can cause serious healthcare associated infections.
Naked viruses
Viruses such as poliovirus that lack a lipid envelope are more resistant to disinfectants. conversely, enveloped viruses, such as HIV, tend to be very sensitive to these chemicals.
Decimal reduction time or D value
the time required for killing 90% of a bacterial population under specific conditions.
the temperature is indicated by a subscript, for example D121.
A one D process reduces the number of cells by one exponent. thus if the D value for an organism is 2 minutes then it would take 4 minutes (2 D values) to reduce a population of 100 (10^2) cells to only one 10^0 survivor.
Critical Instruments
these come into direct contact with body tissues. they include needles and scalpels. critical instruments must be sterile
Semicritical instruments
these come into contact with mucous membranes, but do not penetrate body tissure; they include gastrointestinal endoscopes and endotraceal tubes. semicritical instruments must be free of all viruses and begetative bacteria. the few endospores that may remain pose little risk for infection because mucous membranes are effective barriers against their entry into deeper tissue.
Non-critical instruments and surfaces
these come into contact only with unbroken skin so they pose little risk for infection. countertops, stethoscopes, and blood pressure cuffs are examples of non-critical items.
Moist heat
most heat destroys mocrobes by irreversibly denaturing their proteins. examples of moist heat treatment include boiling, pasteurization, and pressurized steam.
Boiling (moist heat)
Boiling (100 C at sea level) easily destroys most microorganisms and viruses. because of this, drinking water that might be contaminated during floods or other emergency situations should be boiled for at least 5 minutes. boiling is not a method of sterilization, however, because endospores can survive the process.
Pasteurization (moist heat)
Louis Pasteur developed the brief heat treatment we now call pasteurization as a way to prevent spoilage of wine. today pasteurization is still used to destroy heat sensitive spoilage organisms in foods and beverages, increasing the products shelf life without significantly altering its quality. (milks juices etc. preventing tuberculosis, brucellosis, salmonellosis, and typhoid fever.
High temperature-short time (HTST). is used with this, milk cooked to 72 C for 15 seconds.
Shelf stable boxed juices and milk are treated using Ultra high temperature (UHT). This destroys all microorganisms that can grown under normal storage conditions, so it is referred to as ultra pasteurization. The UHT process for milk requires rapidly heating the milk to 140 C, holding it at that temp for a few seconds, then cooling quickly.
Sterilization using pressurized steam (moist heat)
Heat and moisture tolerant items such as surgical instruments etc are sterlized using autoclaves. Water in a chamber in the autoclave is heated to form steam, causing the pressure in the chmber to increase. the higher pressure in turn increases the temperature at which steam forms. steam at atmospheric pressure never exceeds 100 C but steam at an additional 15 psi is 121 C a temperature that kills even endospores. the pressure itself plays no direct role in the killing.
Typical sterilization us 15 psi 121 C for 15 minutes
Commercially sterile
canned foods are commercially sterile meaning that the endospores of some thermophiles may survive. these are usually not a concern, however, because they grow only at temperatures well above those of normal storage.
Dry heat
not as efficient as moist heat in killing microbes.
incineration
burns cell components to ashes. flaming of wire inoculating loops. also used to destroy medical wastes and contaminated animal carcasses
Dry heat ovens
destroys cell components and denatures proteins. less efficient than moist heat, requiring longer times and higher temperatures.
used for laboratory glassware, powders, oils and other dry materials are also sterilized in ovens.
Filtration
Recall that membrane filitration, used to determine the number of bacteria in a liquid medium, retains bacteria while allowing the fluid to pass through. that same principle can be used to physically remove microbes from liquids or air.
Filtration of fluids
used to remove organisms from heat sensitive fluids such as sugar solutions, beer and wine.
Filtration of Air
high efficiency particulate air (HEPA) filters remove nearly all airborne particles that are 0.3 micrometers or larger. these are used for keeping microorganisms out of specialized hospital rooms designed for patients extremely susceptible to infection. the filters are also used in biological safery cabinets in which laboratory personnel work with dangerous airborne pathogens such as Mycobacterium tuberculosis. a continuous stream of incoming and outgoing air flows through HEPA filters to hold microbes within the cabinet. the cabinets are also used to protect samples from contamination.
RADIATION
Radio waves, microwaves, visible and ultraviolet light rays, x rays, and gamma rays are all examples of ELECTROMAGNETIC RADIATION. this is a form of energy that travels in waves and has no mass; the amount of energy is related to the wavelength, which is the distance from crest to crest of a wave. the wavelength is inversely proportional to the frequency, the number of waves per second. radiation that has short waves, and therefor high frequency has jore energy thatn that which has long waves and short frequency. the full range of wavelengths is called the electromagnetic spectrum
Ionizing radiation
Destroys DNA and possibly damages cytoplasmic membranes. produces reactive molecules that damage other cell components. items can be sterilized even after packaging
used to sterilize heat sensitive materials including medical equipment, disposable surgical supplies, and drugs such as penicillin. also used to destroy microbes in spices, herbs, and approved types of produce and meats.
ultraviolet radiation
damages DNA. penetrates poorly
used to destroy microbes in the air and drinking water, and to disinfect surfaces.
High Pressure
high pressure processing is used to decrease the number of microbes in commercial food products such as guacamole, without using high temperatures. the process, which uses pressure of up to 130,000 psi is thought to destroy microbes by denaturing treated products keep the color and flavor associated with fresh foods.
Sterilants
these can destroy all microorganisms, including endospores and viruses. they are also called sporocides. destruction of endospores usually requires a 6-10 hour treatment. sterilants are used to treat heat sensitive critical instruments such as scalpels.
High-level disinfectants
these destroy all viruses and vegetative microorganisms, but they do not reliably kill endospores. most are simply sterilants used for short time periods, not long enough to ensure endospore destruction. they are used to treat semicritical instruments such as gastrointestinal endoscopes
Intermediate level disinfectants
these destroy all vegetative bacteria including mycobacteria, fungi, and most, but not all viruses. they do not kill endospores even with prolonged exposure. this group of germicides is used to disinfect noncritical instruments such as stethoscopes.
Low level disinfectants
these destroy fungi, vegetative bacteria except mycobacteria and eveloped viruses. they do not kill endospores, nor do they always destroy naked viruses. intermediate level and low level disinfectants are also called general purpose disinfectants. in hospitals, they are used for disinfecting furniture floors and walls.
Alcohols
easy to obtain and inexpensive, rapid evaporation limits their contact time.
USED for aqueous solutions of alcohol as used as antiseptics to clean skin in preparation for procedures that break intact skin, and as disinfectants for treating instruments.
Aldehydes (glutaraldehyde, orthophthalaldehyde, and formaldehyde)
capable of destroying all microbes. irritating to the respiratory tract, skin and eyes
Glutaraldehyde and orthophthalaldehyde are used to sterilize medical instruments. formalin is used in vaccine production and to preserve biological specimens.
Biguanides (chlorhexidine)
the most effective of a group of chemicals called biguanides is extensively used in antiseptic products. it stays on skin and mucous membranes, is of relatively low toxicity, and destroys a wide range of microbes, including vegetative bacteria, fungi and some enveloped viruses. Chlorhexidine is an ingredient is many products including antiseptic skin creams, dininfectants, and mouthwashes. Chlorhexidine-imnpregnated catheters and implanted surgical mesh are used in medical procedures. even tiny chips that slowly release chlorohexidine have been developed; these are inserted into periodontal pockets to treat gum disease. adverse side effets of chlorhexidine are rare, but severe allergic reactions have been reported.
