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Explain how bacteria reproduce
- Must have energy source
- Binary fission
- budding
- Aerial spore formation
- Fragmentation of filaments
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List and discuss the physical requirements for bacterial growth
- temperature
- pH
- osmotic pressure
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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
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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
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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
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List and discuss the chemical requirements for bacterial growth
- C
- N, S, P
- trace elements
- oxygen
- organic growth factor
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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
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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
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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
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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
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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
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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
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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
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