Microbial Growth

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Microbial Growth
2
Prokaryotic Growth Media

• Nutrient media used to grow prokaryotes
• Examples Tryptic Soy broth or agar (TSB/TSA),
  nutrient broth or agar
• Contains nutrients prepared for microbial growth
• Energy source
• Essential macronutrients
• Essential micronutrients (trace elements)
• Growth factors
• Importance of sterility
• Sterile No living microbes
• Inoculate using aseptic technique
• Inoculum Introduction of microbes into medium
• Culture
• Microbes growing in/on culture medium

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Agar vs Broth

• Agar
• Complex polysaccharide
• Used as solidifying agent for culture media in
  Petri plates, slants, and deeps
• Generally not metabolized by microbes
• Liquefies at 100C
• Solidifies 40C
• Broth
• Liquid medium

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Types of Growth Media

• Chemically defined
• Exact chemical composition is known
• Used to grow specific prokaryotes and determine
  growth properties
• Tables 6.2 and 6.3 (next slide)
• Complex media
• Nutrients at unknown concentrations and in excess
  (digests of proteins or meat, yeast or plant
  extracts)
• Ex. TSA(B) or Nutrient Agar (B)
• Used to grow a variety of prokaryotes

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Culture Media
Tables 6.2, 6.4
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Selective Media

• Suppress unwanted microbes and encourage desired
  microbes.
• Contains components/conditions that suppress the
  growth of some prokaryotes and allow the growth
  of others
• Used to select for a specific group from a sample
• Staphylococcus aereus grows at high salt
• Staphylococcus aereus can grow on mannitol salt
  agar that has a high concentration of salt the
  growth of other organisms will be inhibited

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Differential Media

• Make it easy to distinguish colonies of different
  microbes.
• Has chemical components that differentiates
  specific types of prokaryotes
• Ex. Blood agar differentiates hemolytic organisms
  form non-hemolytic organisms

Figure 6.9a
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Some media are both selective and differential

• Mannitol salt agar is both selective and
  differential
• Selective
• Staphylococcus aereus can grow on mannitol salt
  agar that has a high concentration of salt the
  growth of other organisms will be inhibited
• Differential
• Staphylococcus aereus ferments mannitol and the
  medium will change color
• Other organisms that grow on high salt will grow
  on mannitol salt agar but may not ferment
  mannitol the media will not change colors

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Growth on MacConkey Agar Selective and
differential Selective Gram positive are
inhibited only gram negative grow
Escherichia coli (E.coli) gram -
Salmonella typhimirium gram -
Differential E.coli appears pinkish-red because
it can Ferment lactose
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Enrichment Media

• Encourages growth of desired microbe
• Used to increase the numbers of specific kinds of
  bacteria from a sample to detectable levels
• Ex. Brain Heart Infusion enriches the growth of
  salt tolerant streptococci
• May also be selective and/or differential

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Pure Culture

• Pure culture
• Come from a single cell
• Streaking for isolation
• Isolated colonies to get a pure culture
• Colony made of approximately 106 cells
• Derived from a single cell

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Streak Plate
Figure 6.10ab