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Microbial Growth Chapter 6

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Is a technique for obtaining pure cultures by diluting by streaking on a Petri plate ... Streak Plate for Isolation: Fig. 6.10. 9/4/09. 33. Preserving Cultures: ... – PowerPoint PPT presentation

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Title: Microbial Growth Chapter 6


1
Microbial Growth Chapter 6
2
Microbial Growth
  • Requirements for Growth
  • Culture Media
  • Growth Patterns
  • Evaluation/Measurement of Growth
  • Lecture 6

3
Physical Requirements for Growth
  • Three realms of requirement
  • Temperature
  • pH
  • Osmotic pressure
  • For all of the three, different groups of
    microorganisms have optimal ranges.

4
Temperature (Fig. 6.1)
5
Temperature
  • Psychrophiles cold-loving microbes
  • Mesophiles moderate temperature loving microbes
  • Thermophiles heat-loving microbes
  • Most species will grow within a limited range
    or _____ Celsius

6
Temperature
  • _________ growth temperature lowest temperature
    at which a species will grow
  • _________ growth temperature temperature at
    which the species grows best
  • _________ growth temperature highest temperature
    at which growth is possible

7
Temperature
  • Psychrophiles two groups
  • True psychrophiles are native to cold
    environments in the Earths deep oceans and polar
    regions
  • Can grow at ____ degrees Celsius, but optimum is
    at 15 degrees C, cant grow above 25 deg. C
  • Psychrotrophs can grow at zero C, but optimum is
    20-30 degrees C, and max is 40 degrees C
  • _____________ organisms

8
Temperature
  • Mesophiles Optimum growth ________C
  • For many pathogens, optimum is body temp. 37C
    (clinical incubators are set at this temp.)
  • Include most common food spoilage organisms (so
    refrigeration works!)
  • Thermophiles optimum 50-60C, many cant grow
    below _________C
  • Spores may survive canning, and may grow is cans
    kept at high temp., but not considered a health
    problem

9
Extreme Thermophiles or Hyperthermophiles
  • Members of the Archaea
  • Optimums of _____C or higher
  • Associated with hot springs and volcanic activity
  • The record Deep sea vent communities growth
    at _____C (water doesnt boil because of extreme
    pressures)

10
pH
  • Most bacteria have a narrow range for optimum
    growth near neutral pH between pH _______________
  • Since bacterial fermentation produces acids,
    natural food preservation is accomplished in
    sauerkraut, pickles and cheeses!
  • Acidophiles record is a chemoautotrophic form
    that lives in the drainage water from coal mines
    at a pH of ________!
  • Molds and yeasts tolerate a wider range and have
    _______ pH optimums

11
Culturing microorganisms and pH
  • Species which produce acids as they grow, will
    create hostile conditions for themselves!
  • __________ are added to growth media
  • Peptones
  • Amino acids
  • Phosphate salts

12
Osmotic Pressure
  • Microorganisms are 80-90 water
  • If too much water leaves the cell, shrinkage
    called _____________occurs
  • When membrane pulls away from cell wall, growth
    is inhibited
  • As a result, high osmotic pressure preserves
    food
  • Salted fish
  • Honey
  • Condensed milk

13
Plasmolysis Fig. 6.4
14
Osmotic Pressure
  • Halophiles (salt lovers)
  • Extreme halophiles or obligate halophiles need up
    to _______ salt
  • Facultative halophiles _______
  • Most need a medium nearly all water
  • _________________ however can cause rupture of
    some types with weak cell walls

15
Chemical Requirements for Growth
  • Carbon
  • ______________ get carbon along with their source
    of energy-organic compounds
  • Chemo- and ________autotrophs get their carbon
    from Carbon dioxide

16
Chemical Requirements for Growth
  • Nitrogen, Phosphorus, Sulfur
  • N 14 of dry weight-mainly _________and__________
    __
  • S, P 4 of dry weight- proteins and nucleic
    acids, cell membranes and ATP
  • Trace elements cofactors/coenzymes- usually
    enough in _________________
  • Organic Growth Factors vitamins, amino acids,
    purines, pyrimindines
  • Nitrogen
  • Decomposed (digested) protein
  • Ammonium ions
  • Nitrate ions
  • Ecologically important relationships..

17
Nitrogen
  • Nitrogen fixation photosynthetic _______bacteria
    and others which live symbiotically within the
    root nodules
  • of such plants as the ________ family convert
    nitrogen gas to usable forms
  • Others groups return the nitrogen to the
    atmosphere. In this way, nitrogen is cycled
    through the _____________.

18
OXYGEN
  • __________ Aerobes require oxygen, growth at or
    near surface of liquid medium, have enzymes to
    deal with the toxic forms of oxygen
  • ____________ aerobes can continue growth without
    oxygen with fermentation or other electron
    acceptors
  • ________ anerobes unable to use oxygen in
    energy manipulating processes and most are HARMED
    by it!

19
HOW OXYGEN causes HARM
  • ________ oxygen high energy and extremely
    reactive form of oxygen(present in phagocytes)
  • Superoxide free radicals very toxic to cellular
    components-neutralized by ___________
  • ______________________ (SOD) converts the
    superoxide into hydrogen peroxide and _____
  • Peroxide broken down by _________ (yields water
    and oxygen)and ____________ (yields water only)

20
Other types of response to oxygen
  • _______________ anerobes dont use oxygen, but
    tolerate it and have enzyme systems for dealing
    with the toxic forms of oxygen
  • ______________ require oxygen, but only in
    concentrations ______ than air. Grow in a narrow
    zone. Sensitive to superoxides and peroxides

21
Summary of Oxygen Relationships Table 6.1
22
Culture Media
  • Vocabulary
  • Culture medium nutrient material prepared in a
    laboratory
  • ___________ microbes introduced inot a culture
    medium
  • ________ treated so that no microorganisms are
    present
  • _____ solidifying agent derived from marine
    algae, composed of a complex, ____________
    polysaccharide

23
Agar
  • Also used a s a thickener in jellies and ice
    cream
  • Melts at 100C and remains liquid until 40-45C
    usually held at ________C
  • ________ agar in a tube at an angle
  • _________ agar in a tube solidified when
    vertical
  • ____________ agar in a Petri dish

24
Media
  • Chemically defined media
  • Exact ____________ composition is known
  • Experimental Laboratory work and autotrophs
    (Table 6.2 and 6.3)
  • Complex media
  • Contains ___________ from yeasts, meat, plants,
    digests of proteins (See Table 6.4)

25
Anerobic Growth
  • Reducing agents such as sodium ___________________
    _which combine with oxygen are part of media
  • For plates
  • Special jar with means to remove ______________
    from around the plates is created and an
    indicator so that removal of oxygen can be
    monitored

26
Special techniques
  • Some bacteria are really difficult
  • Mycobacterium leprae (leprosy) is cultured is in
    ___________________!!!
  • Syphillis spirochete not grown
  • Intracellular parasitic forms Rickettsias and
    chlamydias
  • Carbon dioxide enrichment for forms that live in
    intestinal and respiratory tract
    _________________________
  • Candle jars, chemical packets in bags for plates

27
Candle Jars Fig. 6.7
28
Selective and Differential Media
  • For detection of specific microorganisms
  • _____________ media
  • Examples
  • Bismuth sulfite agar-Salmonella typhi
  • Sabourauds Dextrose agar-pH 5.6 fungi
  • Brilliant Green agar inhibits G, see G-
    Salmonella
  • ____________media make it easier to see a
    desired organism

29
Differential Media
  • Example Blood agar-
  • Streptococcus pyogenes shows a ___________________
    ___ around their colonies where enzymes they have
    secreted have destroyed the red cells

30
Combining Selective and Differential
Qualities Examples
  • Mannitol Salt agar
  • Contains _______ salt and a pH indicator, plus
    mannitol (a sugar)
  • Staph. aureus can tolerate the salt and ferments
    mannitol to form an acid
  • MacConkey agar
  • Contains bile salts and crystal violet and
    lactose
  • Crystal violet and bile salts inhibit __________
  • Lactose fermenters show as red or pink colonies
  • Non-fermenters show as _____________
  • Used to differentiate Salmonella and related
    species

31
Obtaining Pure Cultures
  • Visible colonies theoretically derive from a
    single spore or cell or clump or chain of the
    same species
  • Colonies must be far enough apart to assure they
    are separate
  • _____________________ Is a technique for
    obtaining pure cultures by diluting by streaking
    on a Petri plate
  • Only works if organism is present in large enough
    numbers-otherwise an enrichment step must precede
  • Final step is to remove bacteria from one colony
    to grow in pure culture

32
Streak Plate for Isolation Fig. 6.10
33
Preserving Cultures
  • Deep Freeze -50 to 95C several years
  • ________________(freeze drying) -54 to 72 C
    and water is removed under vacuum. Sealed from
    air, bacteria can live for many years in this form

34
Patterns of Bacterial Growth
  • Binary fission and budding

35
Exponential Growth Fig. 6.13
36
Phases of Growth Fig. 6.14
37
Direct Measurements of Bacterial Growth
  • Plate Counts serial dilution (count 25-250
    colony plates)

38
Pour Plates/Spread Plates Fig. 6.16
39
Most Probable Number (set-up)
40
Most Probable Number (MPN) Fig. 6.18
41
Direct Microscopic Count Fig. 6.19
42
Indirect Methods spectrophotometry
43
Indirect Methods
  • Metabolic activity
  • Amount of product (say CO2 or and acid) is
    assumed to be in direct relationship with the
    number of cells present.)
  • Dry Weight Used for fungi-so that amount of
    growth can be monitored
  • Remove from culture medium, filter, dry and weigh
  • Bacteria can also be monitored in this way and
    are removed from the growth medium (liquid) by
    centrifugation
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