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Microbial Growth - Coggle Diagram
Microbial Growth
Definitions
microbial growth- increase in # of cells, not cell size
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buffers- chemicals (like phosphate salts or peptones) added to lab media to resist changes in pH & enhance growth
temperature abuse- food stays at room temp for several hours, allowing rapid microbial growth
biofilm- structured communities of microorganisms that forms when planktonic (free-floating) cells attach to surfaces; protect organisms from dessication, antibiotics/antiseptics, & host immune system; involved in approx. 70% human bacterial infections; Lactoferrin is a substance that inhibits biofilm formation by binding to iron
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Media Types
complex media- like TSA (tryptic soy agar) plates; any organism can grow; must contain beef extract, soytone, or peptone
chemically defined media- can grow chemo- & photoautotrophs (ex: Simmon's citrate agar); carbon source is citrate
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*if something is not complex, its chemically defined
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Measurement Methods
Serial Dilution Viable Plate Count method most used for measuring bacterial populations; only counts living cells
Viable Plate Count method has one bacterium grows to form one colony forming unit (CFU); only counts live cells
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Pour Plate method good for counting, but not for isolating
Direct Microscopic Count method uses Petroff-Hauser cell counter & is quick and inexpensive but requires high # of bacteria; counts both alive & dead cells
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Different Organisms
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facultative aerobes- prefer oxygen, but not 100% needed
micro-aerophiles- grow without oxygen, can have little oxygen
aerotolerant anaerobes- prefer no oxygen, but can have it
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Bacterial Growth Curve
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- exponential growth or log phase
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Requirements for Growth
Physical (temp, pH, osmotic pressure)
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Staphylococcus aureus is halophilic (salt-loving) & grows well in 7.5% salt conc. & at high osmotic pressure (ham/potato salad)
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Bacillus cereus is large Gram (+) bacillus & forms spores which aren't killed by heating, but germinate as food cools
Chemical (C, N, S, P, oxygen source, trace elements, organic growth factors)
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