Lab 7 Physical factor that control microbial growth

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Lab 7 Physical factor that control microbial
growth
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Microbial growth

• During this lab you will learn how some physical
  factors can influence the growth of bacteria.
• Bacteria have preferences with regard to some
  physical factors
• Oxygen requirement
• Temperature
• Osmotic pressure

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Oxygen requirements

• Obligate aerobe
• Grow only in the presence of oxygen
• Microaerophile
• Require a low concentration of oxygen (2 to
  10). Higher oxygen concentration will inhibit
  their growth and they can not grow in total
  absence of oxygen
• Aerotolerant
• Do not require oxygen but are not bothered by it

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Oxygen requirements

• Facultative anaerobe
• Can grow with or without oxygen but generally do
  better with oxygen
• Obligate anaerobe
• Grow only in the total absence of oxygen

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Oxygen requirement
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Anaerobic (brewer) Jar

• Closed Jar
• Air tight
• Burning candle
• Consume all oxygen
• Anaerobic conditions

http//www.medicalhealthcareinfo.com/content/A_can
dle_jar_is_used_when_cult1.php
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Anaerobic Jar

• Gas-Pak system ? chemical reaction generates
  anaerobic conditions in small plastic jar

http//www.vetmed.wisc.edu/pbs/courses/bact/labman
ual/agp.html
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Thyoglycollate broth

• semi-solid media
• 0.5 agar
• Sodium thioglycollate ? reducing agent that
  maintain a low oxidation-reduction potential in
  the depths of the column for long periods
• Do not agitate! (to minimize oxygen absorption)

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Thyoglycollate broth

• 1. Strict aerobes grow only at the surface
• 2. Facultative anaerobes grow throughout the
  tube, but some do better at the surface
• 3. Aerotolerant grow throughout the tube
• 4. anaerobes grow in lower portion of the tube

http//www.bact.wisc.edu/Microtextbook/images/text
book/growth/thioglycollate.jpg
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Temperature requirement

• Bacteria can usually grow over a wide range of
  temperature
• But often have a temperature at which they grow
  best (divide more rapidly)
• Psychrophilic cold loving (lt 20oC)
• Mesophilic middle loving (30-37oC)
• Thermophilic heat loving (gt 50oC)

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Extreme bacteria
Thermus aquaticus in an hot spring in
Yellowstone. Temperature near boiling water!
Coldest surviving organisms 5 F (-15 C)
Cryptoendoliths
http//whyfiles.org/022critters/hot_bact.html
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Osmotic pressure

• It is the force with which a solvent (water)
  moves from a solution of lower solute
  concentration to a solution of higher solute
  concentration across a semi permeable membrane.
• Hypotonic environment Concentration of solute
  outside the cell is lower than that inside the
  cell.
• Hypertonic environment Concentration of solute
  outside the cell is higher than that inside the
  cell.
• Isotonic environment Concentration of solute
  outside the cell is the same than that inside the
  cell.

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Halophiles bacteria

• Some bacteria like high salt concentration
  halophiles
• Give the color to these ponds used for salt
  production

http//static.flickr.com/19/22731535_b9545fdbba.jp
g
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Objective 1 Oxygen requirements

• 2 BHI plate divided in third inoculate with
  Clostridium perfringes, E. coli, Alcaligenes
  faecalis
• One at 37oC in incubator
• One at 37oC in the brewer Jar
• 1 thyoglycollate broth for each of C. perfringes,
  E. coli, A. faecalis (3 tubes total, 1 bacteria
  per tube)
• Incubate at 37

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Objective 2 Role of temperature

• 4 BHI plates divided into fourth inoculate with
  Serratia marcescens, Micrococcus luteus,
  Pseudomonas fluorescens, Bacillus
  sterathermophilus
• One at 37oC in incubator
• One at 27oC in incubator
• One at 15oC
• One at 55oC

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Objective 3 Osmotic Pressure

• 1 Nutrient Agar plate divided into fourth
  inoculate with S. aureus, S. cerevisiae, E. coli
  and the spore suspension (aspergillus)
• Incubate at 37oC in incubator
• 3 salt concentration plates 5, 10, 15 NaCl
• OR
• 3 sugar concentration plates 10, 25, 50
• divided into fourth inoculate with S. aureus, S
  cerevisiae, E. coli and the spore suspension
  (aspergillus)
• Incubate at 37 in incubator

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Synthesis

• Per group
• 10 plates
• 3 broths
• All the plates will be provided to you pre-made
• Identify them all with your initial, temperature
  of incubation
• Identify each quadrant with the initial of the
  bacteria that you plated in this quadrant
• You do not have to do the 3 streaks technique ?
  just a loose zig-zag
• Your streaks should not touch each other

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Conclusion

• Next lab you will compare the oxygen, temperature
  and the effect of osmolarity in your bacteria