microbial growth chapter 4. objectives what are the factors that influence bacteria growth? oxygen...
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Microbial Growth
Chapter 4
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Objectives
• What are the factors that influence bacteria growth?
• Oxygen requirements
• Nutrient requirements– Carbon, Nitrogen, Sulfur, Phosphorous
• Counting microogranisms
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Microbial Growth
• Growth= an increase in the number of cells, not an increase in size
• Generation=growth by binary fission
• Generation time=time it takes for a cell to divide and the population to double
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Bacteria divide by binary fission
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Biofilms are communities of bacteria
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Examples of Biofilms
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Generation times vary for each organism
• E. coli– 20 minutes (optimal conditions)
• Mycobacterium tuberculosis– 24 hours– 6 week incubation for clinical diagnosis
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Bacterial growth curve
Questions:Antibiotics would have the greatest impact on which phase?Why do microbes enter the stationary phase?At which phase(s) would spores be formed?
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Primary and Secondary metabolites
Metabolites are required for growth Metabolites are required for survival
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Requirements for bacterial growth
• Environmental factors that influence– Temperature, pH, osmotic pressure, oxygen
• Nutritional factors– Carbon, nitrogen, sulfur, and phosphorous– Trace elements
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Optimum Growth Temperatures• Psychrophiles-
– optimum -5 to 15oC
• Psychrotrophs- – range from 20-30oC
• Mesophiles- – range from 25-45oC
• Thermophiles-– range from 45-70oC
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pH influences the growth
• Bacteria-prefer a pH range of 6.5-7.5
• Molds prefer a pH range of 5.0-6.0
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Osmotic environment influences growth
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Oxygen preferences of organisms
• Obligate aerobes
• Facultative anaerobes
• Obligate anaerobes
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Why can some organisms grow in the presence of oxygen?
• Reactive Oxygen Species are byproducts of Aerobic Respiration
• They are extremely toxic to both Prokaryotic and Eukaryotic cells
• DNA Damage Oxidize Amino Acids Inactivate Enzymes Disrupt Membranes Activate Immune System
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Why can some organisms grow in the presence of oxygen?
• Toxic forms of oxygen need to be neutralized by enzymes– Superoxide dismutase
• Accepts electrons to make H2O2
– Catalase• Converts to 4H2O2 to 2H2O + 2O2
– Peroxidase
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Oxygen Preferences of Bacteria
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Candle jars increase CO2 levels for growing capnophiles
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Anaerobic jars eliminate the oxygen for anaerobes to grow.
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Chemical requirements: Carbon
• What are possible sources of carbon?
• Bacteria are classified based on the source of carbon as either heterotrophs or autotrophs
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Classification based on Energy and Carbon sources
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Chemical Requirements: Nitrogen
• Why do bacteria need nitrogen?
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Chemical requirements: Sulfur and Phosphorous
• Why do bacteria need sulfur?
• Why do bacteria need phosphorous?
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Chemical requirements: trace elements
• Small amounts of minerals– Cobalt, zinc, copper, manganese, etc.
• Usually function as cofactors
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Culture Media
• Chemically defined– GSA
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Chemically defined media
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Culture Media
• Complex– Nutrient Agar
– TSA
– BHI
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Culture Media
• Selective • Differential
– Blood
• Selective and Differential– EMB
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Ways to measure bacterial growth
• Direct Count
• Plate Count/Viable Cell Count
• Measure Turbidity
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Direct Counts
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Plate counts require dilutions
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Two techniques for plate counts
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Turbidity gives a rough estimate
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Standard Curves
You may determine the precise concentration of suspension by running knowns amounts and extrapolating data
Nor
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Concentration, mg