Microbial Growth

1
Microbial Growth
2
Growth of Microbes

• Increase in number of cells, not cell size
• One cell becomes colony of millions of cells

3
Growth of Microbes

• Control of growth is important for
• infection control
• growth of industrial and biotech organisms

4
Factors Regulating Growth

• Nutrients
• Environmental conditions temperature, pH,
  osmotic pressure
• Generation time

5
Chemical Requirements

• 1 water!
• Elements
• C (50 of cells dry weight) HONPS
• Trace elements
• Organic
• Source of energy (glucose)
• Vitamins (coenzymes)
• Some amino acids, purines and pyrimidines

6
Nutritional Categories

• Carbon sources
• CO2 autotroph
• organic heterotroph
• Energy sources
• sunlight phototroph
• organic chemotroph

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Nutritional Categories

• Saprobe lives on organic matter of dead
  organisms
• Parasite lives on organic matter of living host
  pathogens

8
Fig. 7.3Movement of WaterOsmosis
9
Fig. 7.4
10
Facilitated diffusion higher to lower
concentration, carrier molecule
11
Active transport lower to higher, takes energy
12
Group translocation lower to higher with
chemical change
13
Bulk transport endocytosis, phagocytosis,
pinocytosis
14
Environmental Factors Influencing Growth

• Temperature
• O2
• pH
• Osmotic Pressure
• Others radiation, atmospheric pressure

15
Temperature Optima

• Psychrophiles cold-loving
• Mesophiles moderate temperature-loving
• Thermophiles heat-loving
• Each has a minimum, optimum, and maximum growth
  temperature

16
Fig. 7.8
17
Temperature Optima

• Optimum growth temperature is usually near the
  top of the growth range
• Death above the maximum temp. comes enzyme
  inactivation
• Mesophiles most common group of organisms
• 40ºF (5C) slows or stops growth of most microbes

18
Microbe of the Day

• Listeria monocytogenes
• Gram rod
• Common in environment
• Lives in monocytes (WBC)

19
Listeria monocytogenes

• Intracellular
• Can move through cell membrane to spread from
  cell to cell

20
Listeria monocytogenes

• Psychrotroph
• Listeriosis fever, aches, GI or CNS symptoms
• Pregnant women may suffer miscarriage

21
Listeria monocytogenes

• Listeriosis
• 2500 cases/yr
• 500 fatal
• Prevention
• Pasteurization
• Avoidance

22
Oxygen Requirements

• Obligate aerobes require O2
• Facultative anaerobes can use O2 but also grow
  without it
• Obligate anaerobes die in the presence of O2

23
Oxygen Tolerance

• Aerotolerant do not use O2 but can grow when it
  is present
• Often ferment glucose to lactic acid
• Microaerophiles require O2 but grow only in
  concentrations lower than air

24
Fig. 7.11
25
Toxic Forms of Oxygen

• Singlet oxygen (O2) very reactive
• Superoxide free radicals (O2.)
• Neutralized by superoxide dismutase (SOD)

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Toxic Forms of Oxygen

• Peroxide anions (O2-2)
• H2O2 broken down by catalase and peroxidase
• Hydroxyl radical (OH-) very reactive

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Brewers Jar
28
Candle jar

• Provides low O2, high CO2

29
pH

• Most bacteria grow between pH 6.5 and 7.5
• Acid (below pH 4) good preservative for pickles,
  sauerkraut, cheeses
• Acidophiles can live at low pH

30
pH

• Many bacteria and viruses survive low pH of
  stomach to infect intestines
• Helicobacter pylori lives in stomach under mucus
  layer

31
Osmotic Pressure

• Bacteria 80-90 water
• High salt in surrounding environment leads to
  water loss and plasmolysis
• Cells plasma membrane shrinks, cell growth
  inhibited

32
Drying and High Osmolarity

• Salted fish, jerky, honey, sweetened condensed
  milk are preserved by pulling water out of
  bacteria
• Hypotonic medium (low osmolarity) may lyse
  bacteria without cell walls

33
Ecological Associations

• Symbiotic close nutritional relationship
• Mutualism both benefit
• Commensalism commensal benefits, host not
  harmed
• Parasitism parasite benefits, host harmed

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Measuring Bacterial Growth
35
Bacterial Division

• Bacteria divide by binary fission
• Alternative means
• Budding
• Conidiospores (filamentous bacteria)
• Fragmentation

36
Fig. 7.13
37
Generation Time

• Time required for cell to divide/for population
  to double
• Average for bacteria is 1-3 hours
• E. coli generation time 20 min
• 20 generations (7 hours), 1 cell becomes 1
  million cells!

38
Fig. 7.14a
39
Fig. 7.14b
40
Bacterial Growth Curve
41
Phases of Growth

• Lag phase making new enzymes in response to new
  medium
• Log phase exponential growth
• Desired for production of products
• Most sensitive to drugs and radiation during this
  period

42
Phases of Growth

• Stationary phase
• nutrients becoming limiting or waste products
  becoming toxic
• death rate division rate
• Death phase death exceeds division

43
Measuring Growth

• Direct methods count individual cells
• Indirect Methods measure effects of bacterial
  growth

44
Fig. i7.6
45
Fig. 7.17
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Fig. 7.16
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Metabolic Activity
48
Dry Weight