Microbial Nutrition and Growth Microbial Population Growth

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Microbial Nutrition and GrowthMicrobial
Population Growth

• Microbiology of the Health Sciences

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The Study of Microbial Growth

• Growth takes place on two levels
• Cell synthesizes new cell components and
  increases in size
• The number of cells in the population increases
• The Basis of Population Growth Binary Fission

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Figure 7.13
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The Rate of Population Growth

• Generation or doubling time The time required
  for a complete fission cycle
• Each new fission cycle or generation increases
  the population by a factor of 2
• As long as the environment is favorable, the
  doubling effect continues at a constant rate
• The length of the generation time- a measure of
  the growth rate of an organism
• Average generation time- 30 to 60 minutes under
  optimum conditions
• Can be as short as 10 to 12 minutes
• This growth pattern is termed exponential

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Basic Nutrients for Growth

• ATP for cellular processes
• Carbon is necessary for the
• production of many
• macromolecules (proteins, lipids,
• and carbohydrates)
• Oxygen for metabolism
• Nitrogen for amino acid synthesis
• Sulfur for vitamins, amino acids,
• structural stability of proteins

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Basic Nutrients for Growth

• Phosphorous makes ATP and membranes
• Trace elements are used for metabolic reaction in
  the
• cell and cell component stabilization
• cobalt Co
• potassium K
• molybdenum Mo
• magnesium Mg
• manganese Mn
• calcium Ca
• iron Fe
• zinc Zn

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Basic Nutrients for Growth

• Organic growth factors such
• as vitamins, amino acids, and
• nucleic acids some growth
• factors cannot be synthesized
• by own cellular processes
• Water
• water activity

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How Microbes Obtain Nutrients

• Heterotroph uses organic
• carbon source
• Autotroph uses inorganic
• carbon dioxide
• Phototroph uses light as energy
• source
• Chemotroph uses chemical
• compounds (ie. glucose)
• Saprobe
• Parasite

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Microbial Nutrition Growth Requirements
INSERT FIGURE 6.1
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Culturing Microorganisms

• Inoculum introduced into medium (broth or solid)
• Environmental specimens
• Clinical specimens
• Stored specimens
• Culture refers to act of cultivating
  microorganisms or the microorganisms that are
  cultivated

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Culturing Microorganisms
INSERT TABLE 6.3
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Culturing Microorganisms

• Special Culture Techniques
• Techniques developed for culturing microorganisms
• Animal and cell culture
• Low-oxygen culture
• Enrichment culture

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Media

• Chemically defined
• Natural
• Living

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Media

• Enriched Media
• added nutrient encourages
• the growth of microorganisms

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Media

• Selective Media
• Selects form a microorganism
• while inhibiting most others
• Phenol Ethanol Agar
• Deoxycholate Agar

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Media

• Differential Media
• Allow for the differentiation of
• microorganisms based on
• action that occurs on the media
• or a color change within the
• media that is based on a pH
• change
• Mannitol Salt Agar
• MacConkey Agar

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Media Question

• What type of media is
• Blood Agar considered?
• Enriched
• Selective
• Differential

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The Population Growth Curve

• A population of bacteria does not maintain its
  potential growth rate and double endlessly
• A population displays a predictable pattern
  called a growth curve
• The method to observe the population growth
  pattern
• Place a tiny number of cells in a sterile liquid
  medium
• Incubate this culture over a period of several
  hours
• Sampling the broth at regular intervals during
  incubation
• Plating each sample onto solid media
• Counting the number of colonies present after
  incubation

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The Rate of Population Growth

• Generation or doubling time The time required
  for a complete fission cycle
• Each new fission cycle or generation increases
  the population by a factor of 2
• As long as the environment is favorable, the
  doubling effect continues at a constant rate
• The length of the generation time- a measure of
  the growth rate of an organism
• Average generation time- 30 to 60 minutes under
  optimum conditions
• Can be as short as 10 to 12 minutes
• This growth pattern is termed exponential

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Stages in the Normal Growth Curve

• Data from an entire growth period typically
• produce a curve with a series of phases
• Lag Phase
• Exponential Growth Phase
• Stationary Growth Phase
• Rapidly Declining Phase
• Death Phase

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Lag Phase

• Relatively flat period
• Newly inoculated cells require a period of
  adjustment, enlargement, and synthesis
• The cells are not yet multiplying at their
  maximum rate
• The population of cells is so sparse that the
  sampling misses them
• Length of lag period varies from one population
  to another

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Exponential Growth (Logarithmic or log) Phase

• When the growth curve increases geometrically
• Cells reach the maximum rate of cell division
• Will continue as long as cells have adequate
  nutrients and the environment is favorable
• The number of cells growing greatly out number
  the number of cells dying.

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Stationary Growth Phase

• The population enters a survival mode in which
  cells stop growing or grow slowly
• The rate of cell inhibition or death balances out
  the rate of multiplication
• Depleted nutrients and oxygen
• Excretion of organic acids and other biochemical
  pollutants into the growth medium
• The number of cells growing will equal the amount
  of cells dying.
• Endospores begin to form in this phase.

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Rapidly Declining Phase

• The curve dips downward
• Cells begin to die at an exponential rate
• The amount of cells dying out numbers the amount
  of cells growing.
• The dead cells become nutrients for the growing
  cells.

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Death Phase

• The curve continues to dips downward
• Most cellular activity stops
• Endospores are formed and released from the
  parent cells.

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Phases of Growth

• Basic phases of growth
• 1. Lag phase new growth medium, period of
  delay while cells prepare to divide
• 2. Log phase (exponential growth phase)
  cellular reproduction most active during this
  period, generation time reaches a constant
  minimum
• 3. Stationary phase state of equilibrium where
  number of cell deaths equals number of cell
  divisions

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Phases of Growth

• Basic phases of growth
• 4. Rapidly Declining Phase cells die
  logarithmically, endospores formed
• 5. Death phase number of deaths exceeds number
  of new cells

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Potential Importance of the Growth Curve

• Implications in microbial control, infection,
  food microbiology, and culture technology
• Growth patterns in microorganisms can account for
  the stages of infection
• Understanding the stages of cell growth is
  crucial for working with cultures
• In some applications, closed batch culturing is
  inefficient, and instead, must use a chemostat or
  continuous culture system

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Graphing Bacterial Growth

• The data from growing bacterial populations are
  graphed by plotting the number of cells as a
  function of time
• If plotted logarithmically- a straight line
• If plotted arithmetically- a constantly curved
  slope
• To calculate thesize of a population over time
  Nf (Ni)2g
• Nf is the total number of cells in the population
  at some point in the growth phase
• Ni is the starting number
• g denotes the generation number

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Population Equation

• Nf Ni (2)g