Exam 2 Practice Test ?s Flashcards
Which of the following is the best definition of generation time?
The length of time it takes a population of cells to double
Microbial growth is measured by
Increased number of cells
What is the equation for determining cell population growth?
Nsubt=Nnaugt X 2^number of generation times
What are the methods to detect and measure microbial growth?
direct cell counts
Viable cell counts
Measuring biomass
Detecting cell products
What are the methods of direct cell counts?
Direct microscope counting–microscope grid
Cell counting instruments–
coulter counter-measures by electric current
Flow cytometer– measures by electric current
What are the methods of viable cell counts?
Plate counts
Spread plate, pour-plate
Colony forming units
Membrane filtration
Most probably number
Serial dilution
Done in 10-fold increments
50,000 cells/ml
Transfer 1ml to 9ml diluent–5,000 cells/ml
Transfer 1ml to 9ml diluent–500 cells/ml
Transfer 1ml to 9ml diluent–50 cells/ml
Transfer 1ml to 9ml diluent–5 cells/ml
Membrane filtration
Good for using to filter natural waters
Filter is placed on agar medium and incubated, colonies form, etc
Most probable number method
Think serial dilution
10 ml 3 or 5 tubes
1 ml 3 or 5 tubes
0.1 ml 3 or 5 tubes
Compare with mpn table
Methods of measuring biomass?
Turbidity
Total weight
Turbidity
Use spectrophotometer
Total weight
Waste of time
detecting cell products
Acid and gas production
ATP - firefly enzyme luciferase
Culture Media
Complex media-tasty soup for microbes
Chemically defined media–exact amounts of pure chemicals
Complex media
Blood agar - differential, not selective
Chocolate - not selective, not differential – for fastidious
MacConkey - selective, differential
Nutrient agar - not selective or differential
Thayer-Martin - for fastidious, selective, not differential
Chemically defined media
Glucose salts
Selective media
Inhibit the growth of certain species
Differential agar
Contains substances that microbes will alter in a recognizable way
Enrichment cultures
Used to isolate an organism present as only a very small fraction of a mixed population
Photo–
Energy source is sunlight
Chemo–
Energy source is chemicals
Chemolitho–
Inorganic chemicals– h2 NH3 NO2^-
Chemoorgano–
Energy source sugars amino acids organic compounds
Classes of germicidal chemicals
Alcohols Aldehydes Biguanides Ethylene Oxide Halogens Metal compounds Ozone Peroxygens Phenolic compounds Quaternary ammonium compounds
