Lecture Exam 3 Flashcards
Bacterial growth
the process in which from a bacterial cell, two equivalent daughter cells are produced.
What are the four different phases in which bacterial growth can be modeled and what happens during each?
- Lag phase - bacteria adapt themselves to growth conditions (individual bacteria are maturing)
- Log phase or exponential phase - individual bacteria are reproducing at their maximum rate so their numbers increase.
- Stationary phase - the growth rate slows due to depletion of nutrients (bacteria begin to exhaust the resources that are available)
- Death phase - bacteria run out of nutrients and die.
On a standard growth curve the vertical axis is labeled as what? What does it stand for?
On the vertical axis growth is shown as L which = log (numbers) where numbers is the number of colony forming units per mL.
On a standard growth curve the horizontal axis is labeled as what? What does it stand for?
T (time)
What are three ways to directly measure bacteria?
- Spread plate technique (broth) cfu/mL
- Filtration
- Hemocytometer
What is a way to indirectly measure bacteria?
Turbidity
Sterilization
removal of all microbial life
Disinfection
removal of pathogens
Antisepsis
removal of pathogens from living tissue
Sanitation
lower microbial counts on eating utensils
What factors do the effectiveness of antimicrobial treatments rely on?
- number of microbes
- type of microbe
- environmental factors
- time of exposure
How do physical or chemical agents inhibit growth?
- effect membrane permeability
- damage proteins
- damage nucleic acids
What are the physical methods to inhibit bacterial growth (microbial control) and how? (be able to list 4-5)
- heat (autoclave, dry heat, pasteurization): moist heat denatures proteins; dry heat kills by oxidation
- low temperature: inhibits microbial growth
- filtration: removes microbes
- high pressure: denatures proteins
- dessication: prevents metabolism
- osmotic pressure: causes plasmolysis
- UV radiation: damages DNA
What are the chemical methods (types of disinfectants) used to inhibit bacterial growth?
- Phenols and phenolics
- Halogens (Iodine and Chlorine)
- Alcohols (ethanol and isopropanol)
- Heavy metals (silver, mercury, copper, zinc and selenium)
- Quaternary ammonium salts
- Aldehydes
- Gaseous Sterilizers
- Peroxygens
Sepsis refers to:
microbial contamination
Asepsis
the absence of significant contamination
What do aseptic surgery techniques prevent?
microbial contamination of wounds
What type of microbes are very difficult to destroy?
Endospores
What type of microbes vary widely in susceptibility to different methods of microbial control?
Vegetative pathogens
What type of environmental influences tend to inhibit antimicrobials?
the presence of organic material such as blood, feces, and saliva
What is Thermal Death Point (TDP)?
Lowest temperature at which all cells in a culture are killed in 10 minutes
What is Thermal Death Time (TDT)?
Time to kill all cells in a culture
What is an autoclave used for?
Steam sterilization
What does pasteurization do?
reduces spoilage organisms and pathogens