Chapter 13: Control of Microbe Growth
How does heat inhibit Microbes?
-Denatures proteins -Alters membranes
How to use Heat to kill microbes?
-Dry-Heat (Bunsen burner, micro incinerator) -Moist-heat ***More effective, because water present in moisture helps denature protein and alter membranes): Autoclave
How does cold control microbial growth?
-Slows microbial metabolism and growth
Pasteurization
-Used for food -does not sterilize the food, but reduces the microbes
Physical methods of controlling microbe growth?
-heat -cold -pressure -desiccatication -radiation -sonication -filtration -phenolics -heavy metals -halogens
The DRT refers to the amount of time it takes to...
...reduce a microbial population by 90%.
The D value is calculated by figuring out how much time it takes to reduce the population by _______
90%
Why is canning a good way to prevent microbial growth?
A pressure canner is recommended because it can destroy both vegetative cells and spores.
Other chemicals that control microbe growth?
Alcohols- denature proteins, best in 70% aqueous solution, degerming, hand sanitizers Surfactants- loosen and lift away microbes, soaps and detergents, low level disinfection, disrupts cell membranes Bisguanides- chlorhexidine used in clinical settings for handwashing or surgical scrub
What is suitable for use on tissues for microbial control to prevent infection?
Antiseptic
Fomite
Any inanimate object to which infectious material adheres and can be transmitted.
Thermal death time (TDT)
At a given temperature, the time it takes to kill all cells in a culture
The disk diffusion assay tests the effectiveness of ________ against a microbe
Chemicals
How do halogens control microbe growth?
Damaging cell molecules *Betadine, bleach, ammonia
(T/F) Soaps are classified as disinfectants.
False
T/F: Moist-heat sterilization protocols require the use of higher temperatures for longer periods of time than do dry-heat sterilization protocols.
False
T/F: Sanitation leaves an object free of microbes
False
Which method neither kills nor inhibits growth of microbes, but instead removes them physically from samples?
Filtration
Bleach is an example of which group of chemicals used for disinfection?
Halogens
Which peroxygens is widely used as a household disinfectant, is inexpensive, and breaks down into water and oxygen gas?
Hydrogen Peroxide
Which type of test is used to determine whether disinfectant solutions actively used in a clinical setting are being used correctly?
In-use test
How do phenolics control microbial growth?
Inhibit microbe growth by disrupting membranes and denaturing proteins *Stable/persistent on surfaces **Phenol can be absorbed by skin and cause nerve damage ***Embedded in kitchen/bath materials, Listerine, Lysol, antibacterial handsoaps (triclosan), and handwashing in hospitals (pHisoHex)
Bacteriostatic
Inhibiting growth of, but not killing, bacteria
How do heavy metals control microbe growth?
Kill microbes by binding to proteins to inhibit enzyme activity. *Mercury, silver, copper, nickel, zinc
Bactericidal
Kills bacteria
How does radiation control microbe growth?
Kills microbes by damaging cellular molecules (forms thymine dimers)
How does pressure control microbial growth?
Kills microbes by denature great proteins
How does sonication control microbe growth?
Kills microbes by lysis
Microbial death is __________
Logarithmic
Thermal Death Point (TDP)
Lowest temperature at which all cells in a culture are killed in 10 min USE TEMP VALUE
What medical items requires sterilization?
Needles
How does filtration control microbe growth?
Removes microbes **HEPA filter: 0.3 um pore size, baceria, spores, viruses, nearly sterile air, used in vacuum HVAC clinic, car, airplane, air purifier ***Membrane filtration— 0.2 um pore, liquids
How does desiccation control microbial growth?
Stops microbe growth by preventing metabolism **dried fruits, meats, fish, canning
Which chemical food preservatives is used in the wine industry but may cause asthmatic reactions in some individuals?
Sulfites
In the disk-diffusion assay, a large zone of inhibition around a disk to which a chemical disinfectant has been applied indicates ____________ of the test microbe to the chemical disinfectant.
Susceptibility or sensitivity
DRT (decimal reduction time)
The amount of time it takes a protocol to kill 90% of the bacterial population.
What term describes the time that is required to kill of the microbes within a sample at a given temperature?
Thermal death time
T/F: Ionizing radiation can penetrate surfaces, but nonionizing radiation cannot.
True
T/F: Mercury-based compounds have fallen out of favor for use as preservatives and antiseptics.
True
Doorknobs and other surfaces in clinical settings are often coated with ________, ________, or ________ to prevent the transmission of microbes.
copper, nickel, zinc
Antisepsis/Degerming
destroys most microbial life, reducing contamination on a living surface
Disinfection
destroys most microbial life, reducing contamination on inanimate surfaces
Sterilization
destruction of all microorganisms and viruses in or on an object
If used for extended periods of time, ________ germicides may lead to sterility.
high level
In an autoclave, the application of pressure to ________ is increased to allow the steam to achieve temperatures above the boiling point of water.
steam
Decontamination/Sanitization
the mechanical removal of most microbes from an animate or inanimate surface
