Microbial growth requires nutrients, favorable environmental conditions, and time. Bacteria multiply through binary fission, dividing into two daughter cells within their generation time, which is typically 1-3 hours. Growth is measured through changes in turbidity, metabolic activity, or dry cell mass over time and passes through lag, log, stationary, and death phases on a standard growth curve. Isolating and culturing microbes on general and differential media allows growth of pure colonies, which can then be identified through observation of morphological and biochemical characteristics. Proper inoculation, isolation, incubation, inspection, and identification techniques are required to produce pure cultures for study.

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 cell’s 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

7. A “Chemoheterotroph”
would…..
• Derive both carbon and energy
from organic compounds

8. A “Chemoorganic autotroph
would be….
Derives energy from organic compounds and
carbon source from inorganic compounds
A related ancient group…..
Lithoautotroph
Neither sunlight nor organics used, rather
it relies totally on inorganics

9. Nutritional Categories
• Saprobe – lives on organic matter
of dead organisms
• Parasite – lives on organic matter
of living host = pathogens

10. Environmental Factors
Influencing Growth
• Temperature
• O2
• pH
• Osmotic Pressure
• Others: radiation, atmospheric
pressure

11. Temperature Optima
• Psychrophiles: cold-loving
• Mesophiles: moderate temperature-
loving
• Thermophiles: heat-loving
• Each has a minimum, optimum,
and maximum growth temperature

12. Fig. 7.8

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

14. Oxygen Requirements
• Obligate aerobes – require O2
• Facultative anaerobes – can use
O2 but also grow without it
• Obligate anaerobes – die in the
presence of O2

15. 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

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

17. Measuring Bacterial Growth

18. Bacterial Division
• Bacteria divide by binary fission
• Alternative means
–Budding
–Conidiospores (filamentous
bacteria)
–Fragmentation

19. Fig. 7.13

20. 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!

21. Fig. 7.14a

22. Plotting growth on graphs

23. Standard Growth Curve

24. 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

25. Phases of Growth
• Stationary phase –
–nutrients becoming limiting or
waste products becoming toxic
– death rate = division rate
• Death phase – death exceeds
division

26. Measuring Growth
• Direct methods – count individual
cells
• Indirect Methods – measure effects
of bacterial growth

27. Fig. i7.6

28. Fig. 7.17

29. Turbidity

30. Metabolic
Activity

31. Dry Weight

32. Culturing Microbes
The Five “I’s
Innoculation: Producing a pure culture
Isolation: Colony on media, one kind of microbe,
pure culture
Incubation: growing microbes under proper
conditions
Inspection: Observation of characteristics (data)
Identification: use of data, correaltion, to ID
organism to exact species
Pure Culture

33. Culturing Microbes
The Five “I’s
Innoculation: Producing a pure culture
Introduce bacteria into a growth medium using “aseptic technique” to
prevent contamination. Tools: Bunsen burner, loop. Needle, etc.

34. Innoculation: Producing a pure culture
Introduce bacteria into a growth medium using “aseptic technique” to
prevent contamination. Tools: Bunsen burner, loop. Needle, etc.

35. Isolation: Colony on media, one kind of
microbe, pure culture: isolation on general
and special “differential media”
General growth media: NA, TSA
Differential: Mac, EMB, SS
These have dyes, salts, inhibiting
agents : see differences on
plates

36. Isolation: Colony on media, one kind of
microbe, pure culture

37. Isolation: Colony on media, one kind of
microbe, pure culture – Streak Plates

38. Isolation: Colony on media, one kind of
microbe, pure culture. Many colonies? Use
a needle, pick one, and redo streak plate

39. Differential: Mac, EMB, SS
These have dyes, salts, inhibiting
agents : see differences on plates

40. • Blood agar : rich with nutrients, can see a
difference, thus differential; much more
later

41. • Incubation: Allow organisms to grow under the optimal
conditions
• Temperature, with or without oxygen etc

42. • Incubation: Allow organisms to grow under the optimal conditions
• Temperature, with or without oxygen etc
• Candle jar reduces oxygen