(exam 1) chapter 7 control of microbial growth Flashcards
what does sepsis mean?
describes bacterial contamination
what does asepsis mean?
absence of (without) significant contamination
what does aseptic technique prevent?
prevent microbial contamination
what is sterilization?
removing and destroying all microbial life (typically commercial sterilization canned goods)
what is disinfection?
destroying harmful microorganisms (typically with chemical disinfectants)
what is sanitation?
lowering microbial counts on eating utensils to safe levels
what is antisepsis?
acts of destroying harmful microorganisms from living tissue (typically with antiseptics)
what is degerming?
the mechanical removal of microbes from a limited area
what is biocide (germicide)?
treatments that kill microbes
what is bacteriostasis?
inhibiting microbe growth (not killing)
what usually causes microbe death and what is the death rate?
heat or chemical; microbes die at a constant rate
what does the effectiveness of the treatment depend on? (four things)
1) number of microbes
2) environment (organic matter- inhibits effectiveness; temperature-heat increases effectiveness; biofilms-protect the microbes)
3) time of exposure
4) microbial characteristics
what are three primary effects of microbial control agents?
1) alterations of membrane permeability (damage to plasma membrane)
2) damage to proteins (enzymes)
3) damage to nucleic acids (can’t replicate)
how does heat control microbial growth?
denatures proteins (denatures enzymes)
what are two moist heat sterilization techniques?
1) boiling
2) free flowing steam (via autoclave)
how does boiling control microbial growth?
denatures proteins- kills most microbes in ~10min BUT endospores are RESISTANT to this method
how does free flowing steam control microbial growth?
uses an autoclave (121 C at 15 psi for 15 min) kills ALL organisms AND ENDOSPORES (but cannot kill prions)
what is an autoclave?
device that uses steam under pressure for sterilization
how does pasteurization (heat) control microbial growth?
Denatures proteins- by using very high temperatures for a short time; Eliminates pathogenic bacteria but
thermoduric organisms survive- used for milk
how does sterilization (heat) control microbial growth?
Kills via oxidation - Ultra-high temps for very short time
(140 C for 4 sec) used for milk in locations where refrigeration is not available
how does dry heat sterilization (heat) control microbe growth?
Burns contaminants to ashes! Kills by oxidation (Flaming, Incineration or Hot-air sterilization)
how does filtration control microbial growth?
passage of substance through a screen-like material (used for heat-sensitive materials)
High-efficiency particulate air (HEPA) filters remove microbes > 0.3 μm in diameter
how do low temperatures control microbial growth?
Have a bacteriostatic effect - stalls their growth
Psychotrophs still grow BUT slowly! Pathogenic bacteria (except Listeria) don’t grow at cold temps “stuns growth”
how does high pressure control microbial growth? What does it alter?
Applies to liquids; Alters protein and carbohydrate molecular structures
how does desiccation control microbial growth?
Without water, microbes can not reproduce but can remain viable
how does Osmotic Pressure
control microbial growth?
(damaging the plasma membrane) high concentrations of salts and sugars cause a hypertonic environment which causes plasmolysis
what are two types of radiation methods to control microbial growth?
1) Ionizing radiation (X-rays, gamma rays, electron beams)
2) Nonionizing radiation (UV light)
how does Ionizing radiation control microbial growth?
(X-rays, gamma rays, electron beams) Ionizes water to create reactive hydroxyl radicals which damages DNA by causing lethal mutations
how does Nonionizing radiation control microbial growth?
(UV light) damages DNA by creating thymine dimers -
Disadvantage: Not very penetrating; microbe must be directly exposed
“Germicidal” lamps
microwaves kill heat BUT
they are not especially antimicrobial
what are the only two chemical methods of controlling microbial growth that we discussed?
1) dilution tests
2) disk-diffusion method
how does dilution tests (chemical methods) control microbial growth?
1) Metal cylinders are dipped into test bacteria and dried
2) Cylinders are placed in disinfectant for 10 min at 20°C
3) Cylinders are transferred to culture media to determine whether the bacteria survived treatment
how does the disk diffusion method (chemical method) control microbial growth?
1) Filter paper disks are soaked in a chemical and placed on a culture
2) Look for zone of inhibition around disks
