micro lecture ch7
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Define the following key terms related to microbial control:
sterilization, disinfection, antisepsis,degerming, sanitization, biocide, germicide, bacteriostasis, and asepsis.
- •Sterilization: destruction or removal of all forms of microbial life, including endospores but with the possible exception of prions; usually done by steam under pressure or a sterilizing gas, such as ethylene oxide
- •Commercial Sterilization: sufficient heat treatment to kill Clostridium botulinum endospores in canned foods; more-resistant endospores of thermophilic bacteria may survive, but they will not germinate and grow under normal storage conditions
- •Disinfection: destruction of vegetative pathogens; Removal of pathogens from inanimate objects (not all is gone tho); may make use of physical or chemical methods
- •Antisepsis: Removal of pathogens from living tissue; tertment is almost always by chemical antimicrobials
- •Degerming: Removal of microbes from a limited area (not killing..just removing), such as skin around an injection site; mostly a mechanical removal by an alcohol-soaked swab
•Sanitization: Lower microbial counts (such as on eating utensils); may be done with high-temp washing or by dipping into a chemical disinfectant
- •Biocide/Germicide: Kills microbes (bio=life; cide=kill) (usually with certain exceptions, such as endospores)
- •Bacteriostasis: Inhibiting, not killing, microbes-once a bacteriostatic agent is removed, growth might resume
asepsis is the absence of significant contamination
Describe the patterns of microbial death caused by treatments with microbial control agents.
- when bacterial populations are heated or treated with antimicrobial chemicals, they usually die at a constant logarithmic rate
- It takes more time to kill a large population of bacteria than it does to kill a small population, because only a fraction of organisms die during a given time interval.
- If death curve is plotted logarithmically, the death rate is constant, as shown by the straight line
Describe the effects of microbial control agents on cellular structures.
–Alternation of membrane permeability-damage to the lipids or proteins of the plasma membrane by antimicrobial agents causes cellular contents to leak into the surrouding medium and interfers with the growth of the cell
–Damage to proteins-bacteria are sometimes thought of as "little bags of enzymes"; enzymes, which are primarily protein, are vital to all cellular activities
–Damage to nucleic acids-damage to these by heat, radiation or chemicals is frequently lethal to the cell; the cell can no longer replicate, nor can it carry out normal metabolic functions such as the synthesis of enzymes
Compare the effectiveness of moist heat (boiling, autoclaving, pasteurization) and dry heat.
moist heat denatures proteins
dry heat kills by oxidation
- moist heat is more effective
Describe how filtration, low temperature, high pressure, desiccation, and osmotic pressure suppress microbial growth.
•Filtration separation of bacteria from suspending liquid. useful for sterilizing liquids (enzymes, vaccines) that are destroyed by heat
•Low temperature inhibits microbial growth
–Refrigeration-metabolic rate of most microbes are reduced so that they cannot reproduce or synthesize toxins (bacteriostatic)
–Deep freezing-rapidly freezing renders microbes dormant but do not necessarily kill them. slow freezing is more harmful bc the ice crystals that form and grow disrupt the cellular and molecular structure of the bacteria
–Lyophilization-aka freeze drying; like freezing but also evaporates all water away-most effective method of long-term preservation of microbial cultures
•High pressure denatures proteins and carbohydrates
•Desiccation (absence of water) prevents metabolism; but can remain viable for years until water is available to them (primarily bacteriostatic)
•Osmotic pressure causes plasmolysis
Explain how radiation kills cells.
- –Ionizing radiation (X rays, gamma rays, electron beams)- destruction of DNA
- –Nonionizing radiation (UV)- damages DNA; can cause mutations
- (Microwaves kill by heat; not especially antimicrobial)
- •Gamma radiation is penetrating and effective but not always practical (or legal) to use.
•UV radiation is not terribly penetrating but generally is safe (and legal) to employ.
•UV disinfection generally is limited to surfaces and shallow (and UV transparent) aqueous solutions (e.g., water).
•Neither is terribly effective against bacterial endospores.
•Contact with either is hazardous to human tissues.
List the factors related to effective disinfection.
- concentration of a disinfectant affects its action, so it should always be diluted exactly as specified
- nature of the material being disinfected; ex: are organic materials present that might interfer with the action of the disinfectant
- the pH of the medium
- whether the disinfectant will easily make contact with the microbes
- disinfection is a gradual process so it may need to be left on for several hours
Interpret results of use-dilution tests and the disk-diffusion method.
- use-dilution tests:
- the effectiveness of the disinfectant can be determined by the number of cultures that grow after it has been disinfected as directed by the manufactor
- A method of determining disinfectant efficacy, and one that isespecially
- useful for determining the ability of disinfectants to kill
- microorganisms dried onto a typical clinical surface (stainless steel)
- 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
- Disinfectants that completely kill (or otherwise remove) microbes at the lowest dilutions (of
- the disinfectant) are considered the most efficaciousused to evaluate the efficacy of a chemical agent
- disk-diffusion: in this experiment, paper disks are soaked in a solution of disinfectant and placed on the surface of a nutrient medium on which a culture of test bacteria has been spread to produce uniform growth
- Used when a large number of isolates are tested for susceptibility to numerous antibiotics. An agar plate is uniformly inoculated with the test organism and a paper disk impregnated with a fixed concentration of an antibiotic is placed on the agar surface. Growth of the organism and diffusion of the antibiotic commence simultaneously resulting in a circular zone of inhibition in which the amount of antibiotic exceeds inhibitory concentrations. The diameter of the inhibition zone is a function of the amount of drug in the disk and
- susceptibility of the microorganism Zone diameter can be correlated with susceptibility as measured by the dilution method. Further correlations using zone diameter allow the designation of an organism as "susceptible", "intermediate", or "resistant" to concentrations of an antibiotic which can be attained in the blood or other body fluids of patients requiring chemotherapy
Identify the methods of action and preferred uses of chemical disinfectants.
Phenol- disruption of plasma membrane, denaturation of enzymes//rarely used except as a standard of comparison; seldom used as a disinfectant or antiseptic bc of its irritating qualities and disagreeable odor
Phenolics-disruption of plasma membrane, denaturation of enzymes//environmental surfaces, instruments, skin surfaces, and mucous membranes; derivatives of phenol that are reactive even in the presence of organic material
Bisphenols-probably disruption of plasma membrane//disinfectant hand soaps and skin lotions; triclosan is an esp common ex. of a bisphenol. broad spectrum but most effective against gram-pos
biguanides (Chlorhexidine)-disruption of plasma membrane//skin disinfection, esp for surgical scrubs; bactericidal to gram-pos and gram-negs; nontoxic, persistent
Differentiate between halogens used as antiseptics and as disinfectants
Iodines are used mainly for skin disinfection and wound treatment (and water treatment)
Chlorine (Cl2), as a gas or in combo with other chemicals, is a widely used disinfectant. Its germicical action iscaused by the hypochlorous acid (HOCl) that forms when chlorine is added to water.
Identifythe appropriate uses for surface-active agents.
soaps and detergents- mechanical removal of microbes thru scrubbing//skin degerming and removal of debris
- acid-anionic sanitizers- not certain; may involve enzyme inactivation or disruption//sanitizers in dairy and food-processing industries; wide spectrum of activity; nontoxic; noncorrosive, fast-acting
- quaternary ammonium compounds (cationic detergents)- enzyme inhibition, protein denaturation, and disruption of plasma membranes//antiseptic for skin, instruments, utensils, rubber goods; bactericidal, bacteriostatic, fungicial and virucidal against enveloped viruses; examples of quats are Zephiran and Cepacol
Explain how microbial control is affected by the type of microbe.
antimicrobials that are lipid-soluable are more likely to be effective against enveloped viruses. Nonenveloped viruses, which have only a protein coat, are more resistant-fewer biocides are active against them.
the process of removing or destroying all microbial life on an object
commercial sterilization is only killing the C. Botulinum endospores
the process of reducing or inhibiting microbial growth on a nonliving surface
lower microbial counts on eating utensils
the process of reducing or inhibiting microorganism on living tissue
removal of microbes from a limited area, such as the skin around an injection site
- killing of germs
- -cide is means to kill
the absence of significant contamination
what keeps the cell's insides in and outsides out
this membrane actively regulates the passage of nutrients into the cell and the elimination of wastes from the cel. Damage to the lipids or proteins of the plasma membrane by antimicrobial agents causes cellular contents to leak into the surrounding medium and interferes with the growth of the cell
utilizes steam under pressure to sterilize things
absence of water
- Xrays, gamma rays, electron beams
- Radiation consisting of particles, X-rays, or gamma rays with sufficient energy to cause ionization in the medium through which it passes.
- destroys DNA
- Non-ionizing radiation or non-ionising radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules -- that is, to completely remove an electron from an atom or molecule
- Damages DNA
kill by heat, not esp. antimicrobial
- phenol is carbolic acid
- phenolics are derivatives of phenol that contain a molecule of penol that has been chemically altered to reduce its irritating qualities or increase its antibacterial activity in combo with a soap or detergent
- derivatives of phenol that contain two phenolic groups connected by a bridge
- Used for disinfectant hand soaps and skin loctions
- triclosan is an esp common ex. of one. It has a broad spectrum, but most effective agaisnt gram-pos
have a broad spectrum of activity, with a mode of action primarily affecting bacterial cell membranes
some include: Chlorhexidine and Alexidine
- Used for skin disinfection, esp for surgical scrubs
- Bactericidal to gram-pos and gram-neg; nontoxic, persistent
- the best known biguanide, frequently used for microbial control on skin and mucous membranes
- combined with a detergen or alcohol, it is much used for surgical hand scrubs and preoperative skin prep in patients
particularly iodine and chlorine, are effective antimicrobial agents, both alone and as constituents of inorganic or organic compounds
- aka surfactants
- decrease surface tension amoung molecules of a liquid
- such agents include soaps and detergents
- Quaternary Ammonium Compounds
- the most widely used surface-agents are cationic agents such as QUATs
- strongly bactericidal against gram-pos and less active against gram-neg
- among the most effective antimicrobials
- two ex. are formaldehyde and glutaraldehyde
- they inactivate proteins by forming covalent cross-links with several organic functional groups on proteins
- formaldehyde gass is an excellent disinfectant
- glutaraldehyde is a chemical relative of formaldehyde that is less
- irritating and more effective than formaldehyde. It is used to disinfect
- hospital instruments, including endoscopes and respiratory therapy
- equipment, but they must be carefully cleaned first
- from a group of oxidizing agents called peroxygens
- not good antiseptic for open wounds
- it is quickly broken down to water and gaseous oxygen by the action of the enzyme catalse
- effectively disinfects inanimate objects; in such applications, it is even sporicidal at high concentrations
Heated, it can be used as a gaseous sterilant
A substance consisting of iodine and a solubilizing agent that releases free iodine when in solution
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