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Physical & Chemical Control of Microbes
Terms in this set (43)
Relative resistance of microbes
-bacterial spores and prions
-protozoan cysts, fungal sexual spores, naked viruses
-most bacterial vegetative cells
-fingal nonsexual spores and hyphae, enveloped viruses, yeast, protozoan trophozoites
-A process that destroys or removes all viable microorganisms, including spores and viruses; microbicidal
-Usually used with inanimate objects
-Use of physical process (such as UV) or chemical agent (disinfectant) to destroy vegetative pathogens, toxins, but usually not endospors; used with inanimate objects
-Chemical agents (antiseptics) destroy or inhibit vegetative pathogen, but mild enough to be used on skin and mucous membranes.
microbistatic vs. microbicidal agents
=Temporarily prevents growth of microbes, but does not necessarily kill
=Exert its function through killing or destroying organism
definition of microbial death
permanent loss of reproductive capability, no growth when checked under optimum growth conditions
Mode of action (cellular target):
Cell wall, Cell Membrane, or Protein Function
(or Nucleic acid synthesis, protein synthesis)
How do surfactants affect cells (what is the cellular target?)
destroy membrane integrity by interacting with lipid molecules. (target cell membrane)
How are proteins and enzymes affected by high temperature, extreme pH, and heavy metals?
the physical agents (heat, extreme pH) can lead to protein denaturation,
while the chemical agents (metallic ions: heavy metals) can block active sit of enzymes and inactivate them.
What is protein denaturation?
complete loss of function
How do penicillins and lysozyme affect bacterial cells?
What are the conditions used in autoclave?
121 *C, 20 psi, 15-30 min
Comparison of sterilization methods using dry heat and moist heat: which one requires longer exposure and higher temperature to sterilize objects?
Dry heat requires higher temp for longer time than moist heat.
Moist heat is more effective and temp and time of exposure is less than dry heat.
How does cold temperature affect microbes?
It will NOT kill bacteria. It simply PRESERVES them.
Is refrigeration microbiocidal or microbiostatic?
(remember: microbiocidal, -cidal = killing, and refrigeration does NOT kill bacteria!)
Differences between ionizing radiation (gamma-ray) and UV irradiation
Ionizing = sterilization
Nonionizing (UV) = disinfectant
Nonionizing radiation (UV)
CANNOT penetrate (this, not effective against endospores)
Can penetrate liquids and solids effectively
How does ionizing radiation affect cells?
Ejects orbital electrons from an atom.
-ionizes molecules, breaks DNA strands, causes mutations or death
What is the specific cellular damage caused by UV exposure?
-Causes formation of pyrimidine dimers on DNA strands, leads to mutations actively dividing cells
-Could lead to microbial death
-in human, UV exposure causes skin cell death or cancerous mutations
What is the consequence of UV exposure in microorganisms?
could lead to microbial death
(not effective against endospores)
What is the consequence of UV exposure in human?
causes skin cell death or cancerous mutations
To which organisms UV is not effective?
Why isn't UV considered as an effective sterilization method?
Because it is unable to kill endospores.
Examples of applications of filtration sterilization
-Sterilize liquids that are sensitive to heat
*Serum, vaccines, media, antibiotic solutions
Modes of action (mechanisms):
How does bleach or iodine affect microbial cells? How about lysol (phenolics)?
What's the mechanism for alcohol disinfection?
A surfactant, dissolves membrane lipids, disrupts cell surface tension, denatures proteins
What is the effective concentration range for alcohol disinfection?
(never 100% because requires water to become active)
What is the mechanism for hydrogen peroxide as a sterilant?
Reactive oxygen species
high concentration (25%) to be sterilant
Why are anaerobes more sensitive to hydrogen peroxide killing?
Because Hydrogen Peroxide is a reactive oxygen species
Structure of a quat molecule (such as benzalkonium chloride) and how does it cause damage to cells (cell target)?
Structure: cationic detergents
*Bind and disrupt cell membrane
How do heavy metals cause damages to cells?
Can inactivate enzymes at very low concentrations
Which organisms are more susceptible to dyes?
___ can be more resistant than spores because of _____.
Can skin be sterilized?
No, it is impossible.
What is pasteurization used for?
Disinfection of beverages.
Is pasteurization a steriliization method?
It does not kill endospores or many nonpathogenic microbes.
_____ is the most common form of specific cellular damage caused by UV.
Use filter membranes to remove microbes and spores from LIQUIDS and AIR
-does NOT kill, but does REMOVE
-convenient and doesn't destroy
How does bleach or iodine affect microbial cells?
Disrupt protein function!
(disrupt sulfahydryl groups in amino acids)
How does lysol (phenolics) affect microbial cells?
Disrupt cell wall and membranes & precipitate proteins!
Quats are ____
For quats, the positive charge region binds _____ and the _____ region integrates into the _____.
+ region binds bacteria and the
uncharged region integrates into the cell membrane.
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