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Microbial Growth

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Microbial Growth Chapter 6 Growth Requirements Physical Temperature Optimum growth temperature- temperature at which the organism grows its best Psychrophiles- cold ... – PowerPoint PPT presentation

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Title: Microbial Growth


1
Microbial Growth
  • Chapter 6

2
Growth Requirements
  • Physical
  • Temperature
  • Optimum growth temperature- temperature at which
    the organism grows its best
  • Psychrophiles- cold loving- range from 10 ºC to
    lt 20 ºC optimum 15 ºC
  • Mesophiles- moderate-temperature-loving- optimum
    25-40 ºC most common
  • Thermophiles- heat-loving- optimum 50-60 ºC
  • Psychotrophs- range from 0 ºC to lt 40 ºC
    responsible for food spoilage

3
Growth Requirements (cont.)
  • pH- most bacteria grow best between pH 6.5 and
    7.5 fungi prefer more acidic environments,
    optimum pH, 5-6
  • Acidophiles- acid loving can live as low as pH
    1, e.g. coal mines
  • Osmotic pressure
  • Halophiles- salt-loving- some can grow in as much
    as 30 NaCl

4
Fig. 6.1 Typical growth rates
5
Fig. 6.2 Food Spoilage Temperature
6
Fig. 6.3 The effect of the amount of food on its
cooling rate
7
Fig. 6.4 Plasmolysis
8
Chemical
  • Water
  • Carbon sources
  • Heterotrophs-organics
  • Autotrophs- CO2
  • Sources of
  • Nitrogen- amino acids, nucleic acids
  • Sulfur- amino acids, vitamins
  • Phosphorous- ATP

9
Chemical (cont.)
  • Trace elements- cofactors iron, copper, zinc
  • Oxygen- Obligate aerobes
  • Anaerobes
  • Facultative anaerobes- use oxygen but can grow
    without it by fermentation or anaerobic
    respiration have catalase and SOD, e.g. E. coli
  • Obligate anaerobes- lack enzymes to neutralize
    toxic forms of oxygen
  • Aerotolerant anaerobes- tolerates oxygen SOD
  • Microaerophilic aerobes- low oxygen concentration
  • Enzymes-
  • Organic growth factors- e.g. vitamins, purines

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11
Enzymes
  • Superoxide dismutase- SOD- convert the superoxide
    free radical into molecular oxygen and hydrogen
    peroxide
  • Catalase- converts hydrogen peroxide into water
    and oxygen
  • Peroxidase- breaks down hydrogen peroxide into
    water

12
Culture Media
  • Types
  • Agar- solid or semisolid
  • Plates, test tubes (deep or slanted)
  • Broth- liquid- NO agar
  • Chemically defined media- media whose exact
    composition is known
  • Useful for fastidious organisms
  • Complex media- nutrients derived from a variety
    of extracts can vary slightly from one batch to
    the next
  • Nutrient broth- NB
  • Nutrient agar- NA

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16
Anaerobic Growth Media
  • Reducing media- contains ingredients such as
    sodium thioglycolate to help deplete the oxygen
    from the culture medium
  • Anaerobe jar- contains chemicals in a packet that
    generate hydrogen and carbon dioxide when mixed
    with water the hydrogen then reacts with the
    oxygen present in the air and forms water, thus
    removing oxygen from the jar
  • Anaerobe chamber- equipped with air locks and
    gases used when handling a lot of cultures

17
Fig. 6.5 Anaerobic jar
18
Fig. 6.6 An anaerobic chamber
19
Special Culture Techniques
  • Capnophiles- microorganisms that grow better at
    high CO2 concentrations
  • Carbon dioxide incubators
  • Candle jar

20
Fig. 6.7b CO2 generating packet
21
Fig. 6.7a Candle Jar
22
Selective Media- used to suppress the growth of
unwanted bacteria and encourage the growth of the
desired organism
  • Bismuth sulfite agar
  • Inhibits Gram and most G- bacteria
  • Used to isolate Salmonella typhi
  • Sabouraud glucose agar
  • has a pH of 5.6 which inhibits most bacteria
  • used to isolate fungi
  • Brilliant Green Agar
  • inhibits G
  • Used to isolate Salmonella spp.

23
Differential Media
  • Medium that makes it easier to distinguish
    colonies of the desired organism
  • Blood agar
  • used to identify organisms that lyse RBCs
  • E.g. Streptococcus pyogenes

24
Fig. 6.8 Blood agar, a differential medium
containing RBCs.
25
Selective and Differential Media
  • Mannitol salt agar (MSA)
  • contains 7.5 NaCl- inhibitory
  • contains mannitol- carbon source
  • contains pH indicator that changes color if acid
    is produced from the fermentation of mannitol
  • organisms that can tolerate high concentrations
    of salt (selective component) and ferment
    mannitol (differential component) are likely to
    be Staphylococcus aureus

26
MacConkey agar
  • Contains bile salts and crystal violet which
    inhibits G bacteria (selective)
  • Contains lactose (differential)
  • lactose fermenters appear as pink colonies e.g.
    E. coli
  • non-lactose fermenters appear as colorless
    colonies

27
Fig. 6.9 Bacterial colonies on several different
media.
28
Enrichment Media
  • Provides nutrients and environmental conditions
    that favor the growth of a particular
    microorganism and not others encourages the
    growth of all bacteria present in a sample

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30
Cultures
  • Pure cultures
  • Colony- arises from a single cell or groups of
    cells
  • Streak Plate method- used to isolate colonies
  • Preservation
  • Deep-freezing- liquid suspension frozen 50 ºC to
    70 ºC lasts for years
  • Lyophilization- freeze-drying- suspension is
    quickly frozen and then sublimated- powder like
    product lasts for years and the suspension can be
    hydrated to revive the microorganism
  • Growth
  • Bacterial division- binary fission
  • Generation time- the time required for a cell to
    divide
  • Logarithmic growth

31
Fig. 6.10 Streak Plate Method
32
Fig. 6.11 Binary Fission in Bacteria
33
Fig. 6.12 Cell Division
34
Growth Curve
  • Lag phase- period of little or no division
  • Log phase
  • logarithmic increase in the number of bacteria
    exponential
  • Stationary phase
  • The number of bacteria being produced equals the
    number of bacteria dying
  • Death or decline phase
  • Logarithmic decrease in the number of bacteria

35
Fig. 6.14 Bacterial Growth Curve
36
Measurement of Growth
  • Plate counts- measures viable cells CFU- colony
    forming units
  • Serial dilutions- uses diluted samples
  • Pour plates and spread plates-
  • Filtration- used for samples with low microbial
    numbers filter concentrates the microorganism
  • Most Probable Number (MPN)
  • Direct microscopic counts- direct enumeration of
    the cells

37
Fig. 6.15 Plate counts and serial dilutions
38
Fig. 6.16 Methods for Plate counts
39
Fig. 6.17 Counting bacteria by filtration.
40
Fig. 6.18 MPN Method
41
Fig. 6.19 Direct microscopic counts
42
Estimating Bacterial Numbers by Indirect Methods
  • Turbidity
  • Metabolic activity
  • Dry weight
  • Urine culture colony estimates
  • 10,000 or below- contamination
  • 10,000-100,000- not conclusive
  • gt 100,000 - infection

43
Fig. 6.20 Turbidity estimation of bacterial
numbers.
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