Card Set Information

2012-09-26 15:24:00

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  1. Explain how bacteria reproduce
    • Must have energy source
    • Binary fission
    • budding
    • Aerial spore formation
    • Fragmentation of filaments
  2. List and discuss the physical requirements for bacterial growth
    • temperature
    • pH
    • osmotic pressure
  3. Classify microbes on the basis of preferred temperature range
    • Psychrophiles: -10 to 20
    • Psychrotrophes: 0 to 30 (most likely to cause food spoilage from being in fridge)
    • Mesophiles: 10 to 50 (most likely to be pathogenic to humans - body temp)
    • Thermophiles: 40-70
    • Hyperthermophiles: 65-110
  4. Explain how and why the pH of culture media is controlled
    • Most bacteria grow between pH 6.5-7.5
    • All growth media include buffers to prevent drop in pH due to bacterial metabolism products.
    • Acidophiles grow in acidic environments
    • Molds and yests grow between pH 5-6
  5. Explain the importance of osmotic pressure to microbial growth
    • Bacteria are sensitive to changes in osmotic pressure
    • Hypertonic solutions cause plasmolysis
    • Hoptonic solutions cause osmolysis
  6. List and discuss the chemical requirements for bacterial growth
    • C
    • N, S, P
    • trace elements
    • oxygen
    • organic growth factor
  7. List and discuss the categories of bacteria based on oxygen requirements
    • Obligate aerobes: need O2
    • Facultative anaerobes: like O2 (more growth, more ATP), but can perform anaerobic growth
    • Obligate anaerobes: O2 is toxic
    • Aerotolerant anaerobes: only anaerobic growth, but isn't killed by O2
    • Microaerophiles: only aerobic growth, but O2 required in a very small amount
  8. Give the toxic forms of oxygen
    • Singlet oxygen: 1O2- has been boosted to a higher energy state and is HIGHLY reactive
    • Superoxide free radicals: O2-*  (superoxide dismutase is enzyme that fixes)
    • Peroxide anion: O22- (catalase and peroxidase are enzymes that fix)
    • Hydroxyl radical: OH* most reactive, formed by ionizing radiation applied to water
  9. Define selective and differential medium, and give examples of each including purpose and results expected
    • Selective media: suppress growth of unwanted microbes (include salts, dyes, or other chemicals)
    • Differential media: used to distinguish colonies of different microbes (multiple colonies grow, but have different effects on the media)
    • Eosin Methylene Blue: different colors show if lactose has been fermented
    • Mannitol salt agar: selective due to high salt, pH indicator shows if Mannitol has been fermented
    • Blood agar: differential shows amount of hemolysis that has occurred
  10. Describe the methods for growing anaerobes
    • Reducing media: contain chemicals that combine with and remove O2 from the medium, heated to drive off O2
    • Anaerobic jar: envelope containing chemicals uses O2 and creates CO2
    • Anaerobic chamber: Filled with inert, O2-free gas (gives a place to work with the bacteria sealed from environment
  11. List and describe ways bacteria are preserved
    • Refrigeration: short-term storage
    • Deep-freezing: -50 to -95
    • Lyophilization (freeze-drying): frozen (-54 to -72) and dehydrated in a vacuum
  12. Draw the bacterial growth curve and explain the events in each of the 4 phases
    • Lag phase: # bacteria not increasing, but high metabolic rxns occur to prepare for log phase
    • Log phase: logarithmic increase in population
    • Stationary phase: bacterial growth in equilibrium with bacterial death
    • Death phase: population is decreasing at a logarithmic rate
  13. Differentiate between direct and indirect methods for measuring bnacterial growth and list and describe at  least 2 different methods for each.
    • Direct: standard plate count, filtration, most probable number, direct microscopic count
    • Standard plate count: measure number of viable bacteria.  Perform serial dilutions, then count plate that has 25-250 colonies
    • Filtration: for samples containing very small bacterial #, placed through filter then counted
    • Most probably number: statistical estimation of bacteria that grow in liquid medium (count positive tubes, compare results with MPN table)
    • Direct microscopic count: uses specially designed slides with squares.  #cells counted / volume area counted = number of bacteria per mL
    • Indirect: turbidity, metabolic activity, dry weight
    • Turbidity: light passed through tube into spectophotometer
    • Metabolic activity: estimate based on amount of metabolic product produced OR oxygen consumed
    • Dry weight: microbial sample is filtered/dried/weighed and compare to literature value