Differential Media Blood Agar

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Differential Media Blood Agar
Alpha hemolysis

• Blood agar detects
• production found in
  some Streptococcus sp.
• Some (mostly harmless) Streptococcus cause
• Pathogenic S. pyrogenes causes
• Non-Streptococcus sp. cause

Beta hemolysis
Gamma hemolysis
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Selective Media SDA
SDA
NA
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Selective and Differential Media MacConkey Agar
NA
MacConkey
MacConkey
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Atmospheric Conditions

• High CO2 some O2
• Enhances growth of many medically-important
  species
• Candle jar
• very low
  concentrations of O2
• Special airtight jar with H2 and CO2
• no O2 at
  all
• Anaerobic chamber
• Addition of reducing agents to culture medium
  eliminate O2

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Enrichment cultures
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Binary Fission
Ave. time
time it takes
for a population to double in number E. coli can
double in Mycobacterium tuberculosis require
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Binary Fission in Action!
Figure 6.17
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Exponential Growth of Bacteria
Arithmetic vs. logarithmic growth

• number of cells in population at a
  given time
• original number of cells in population
• number of divisions cells have undergone
  during that time

Figure 6.18
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Phases of Microbial Growth
Figure 6.20
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Bacterial Growth in the Laboratory

• Cells synthesize macromolecules needed to
  replication
• Phase length depends on original and new
  conditions
• Cells divide at a constant rate ? population
  increases logarithmically
• Cells increase mass ? production of proteins,
  etc.
• Nutrients are used and waste products are
  produced
• Late log phase cells prepare to enter
  stationary phase
• May initiate sporulation or otherwise prepare for
  starvation conditions
• May produce antibiotics to kill other organisms
  (get rid of competition!)

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Bacterial Growth in the Laboratory

• Supply of nutrients and energy has been exhausted
• Waste products accumulate
• Total number of cells remains constant
• Length of time varies with species and
  environmental conditions
• Total number of viable cells decreases
• Cells die at constant rate
• All cells may die or some may survive (endospores)

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How to detect and measure growth?

• quantify
  number of cells
• Viable plate counts
• Membrane filtration
• Microscope and counting chamber
• Coulter Counter (automated counting machine)
• Most probable number (MPN)
• 
  correlate growth with number of organisms
• Metabolic activity
• Wet or dry weight
• Turbidity

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Direct Methods Viable Plate Counts
Figure 6.21
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Direct Methods Most Probable Number
Figure 6.24
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Most Probable Number table
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Indirect Methods - Turbidity

• Turbidity cloudiness of bacterial suspension
• Spectrophotometer measures amount of light
  passing through suspension ? optical density (OD)

Turbidity
Spectrophotometer