Flashcards in Ch 07 Microbial Growth Deck (56)
What does labile mean?
In what situation if filtration the only way to eliminate microbes?
When dealing with heat labile microbes.
What does sepsis mean?
What does asepis mean?
Free of contamination.
What does sterilization mean?
Removing all microbes.
What does disinfection mean?
Removing pathogens off objects.
What does antisepsis mean?
Removing pathogens from living tissue.
What does degerming mean?
Removing microbes from a limited area. Hanswashing.
What does sanitation mean?
Lowering microbe counts on eating utensils.
What is meant by biocide/germicide?
What is meant by bacteriostasis?
Inhibiting, not killing, microbes.
The usual definition of sterilization is the removal or destruction of all forms of microbial life; how could there be practical exceptions to this simple definition?
Sterilization implies to the absence of prions, tough to do.
Describe the rate of microbial death caused by treatments with microbial control agents.
Microorganisms die at a constant rate.
Name four params microbial treatments depends upon.
Number of microbes
Time of exposure
Which microbes are chemically resistant?
Which are physically resistant?
Chem: Gram-neg, capsules
How is it possible that a solution containing a million bacteria would take longer to sterilize than one containing a half-million bacteria?
Rate of microbial death: The number of microbes. The more microbes to begin with, the longer it takes to eliminate the entire population.
other factors: environment influences; time of exposure; microbial characteristics.
Describe the effects of microbial control agents on cellular structures.
- Attacking the cell wall
- Alteration of membrane permeability
- Damage to proteins
- Damage to nucleic acids
Would a chemical microbial control agent that affects plasma membranes affect humans?
Yes because all cells including human cells have plasma membrane. Anything that attacks the plasma membrane will attack you.
It is important to develop a microbial agent that targets components of the microorganism that are not present in the host cell.
What are three methods to kill microbes?
Cell membrane damage
Nucleic acid damage
Describe Thermal Death Point (TDP), Thermal Death Time (TDT) and Decimal Reduction Time, (DRT)?
Thermal Death Point: lowest temp which all cells are killed in 10 minutes.
Thermal Death Time: time which all cells are killed.
Decimal Reduction Time: minutes to kill 90% of population.
How does an autoclave work?
Heat: 121 C.
Pressure: 15 PSI
What is Pasteurization?
Reduces spoilage, does not sterilize.
How does dry heat kill?
What are physical methods of microbial control?
Differentiate ionization from nonionization radiation.
Ion: short WL, X-rays 200 nm
Non: UV, 260 nm
What are the principles of effective disinfection ?
Principles of effective disinfection:
1. Concentration of disinfection
2. Nature of the material- organic materials present that might interfere with the action of the disinfectant
4. Time- disinfection is a gradual process
Interpret the results of use-dilution test and disk-diffusion method
Use-dilution: metal/glass cylinders dipped into cultures of test bacteria and then dried. placed into a soution of the disinfectant for ten minutes then transfered to a medium that permits growth of any surviving bacteria. the effectiveness of the disinfectatnt is determined by the number of cultures that can grow (more cultures that grow, less effective it is)
Disk-diffusion: paper disks soaked in chemical and placed on agar plate that has previously been incubated and innoculated with the test organism. after incubation, if test is effective, a clear zone represendting inhibition of growth can be seen around the plate.
Interpret the results of use-dilution test.
Cylinders dipped into cultures of test bacteria and then dried. placed into a solution of the disinfectant for ten minutes then transferred to a medium that permits growth of any surviving bacteria. the effectiveness of the disinfectant is determined by the number of cultures that can grow.
Interpret the results of disk-diffusion method.
Paper disks soaked in chemical and placed on agar plate that has previously been incubated and inoculated with the test organism. after incubation, if test is effective, a clear zone representing inhibition of growth can be seen around the plate.