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Microbial Growth - Coggle Diagram
Microbial Growth
Requirements for Growth
Physical: temp, pH, osmotic pressure
Chemical: C,N,S,P, o2 sources, trace elements, organic growth factors
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Buffers: chemicals (phosphate salts/peptones) added to lab media to resist changes in pH and enhance growth
Temperature abuse: food that stays between prepared or room temp for several hrs, allowing rapid microbial growth
Staphylococcus aureus- halophilic (salt-loving) growing well in 7.5% salt and high osmotic pressure (ham, potato salad)
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Bacillus cereus, gastroenteritis bacillus, forms spores that are not killed by heating but germinates as the food cools down
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Biofilms/ communication
Quorum sensing= communication between bacteria in a biofilm using chemical signals (acts as community, coordinate activities to "group" together
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Biofilsm are a structured community that form when planktonic cells attach to surfaces (rocks, teeth, tiles in showers)
Biolfims protect microorganisms from desiccation, antibiotics/septics, and the host immune system (environmental factors) * can exchange DNA info in plasmid
Planktonic bacteria are typically more susceptible to antibiotics and disinfectants (move independently)
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in Lab, bacteria are typically grown as planktonic cells, which are free floating (in a liquid environment)
Measurement Methods:
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direct mircoscopic count using Petroff-Hauser cel counter is quick and inexpensive but requires a high number of bacteria and counts both DEAD/LIVE cells (estimate)
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Spectrophotometer: used to provide a graph estimate of bacterial numbers by measuring turbidity (indirect estimate)
Serial dilution viable plate count method= most frequnetly used for measuring bacterial pops. (best technique to count LIVE cells
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Biofilm examples
Barbon dioxide rich culture chambers (at home)- with candle NO O2, ONLY CO2
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Anaerobic chamber (in lab)- methylene blue > changes from blue to yellow when inside the jar is pure CO2. absorbing O2, releasing CO2
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