1. Microbial Nutrition and Growth Microbial Population Growth
Microbiology of the Health Sciences

2. The Study of Microbial Growth
Growth takes place on two levels
Cell synthesizes new cell components and increases in size
The number of cells in the population increases
The Basis of Population Growth: Binary Fission

3. Figure 7.13

4. The Rate of Population Growth
Generation or doubling time: The time required for a complete fission cycle
Each new fission cycle or generation increases the population by a factor of 2
As long as the environment is favorable, the doubling effect continues at a constant rate
The length of the generation time- a measure of the growth rate of an organism
Average generation time- 30 to 60 minutes under optimum conditions
Can be as short as 10 to 12 minutes
This growth pattern is termed exponential

5. Basic Nutrients for Growth
ATP for cellular processes Carbon is necessary for the production of many macromolecules (proteins, lipids, and carbohydrates) Oxygen for metabolism Nitrogen for amino acid synthesis Sulfur for vitamins, amino acids, structural stability of proteins

6. Basic Nutrients for Growth
Phosphorous makes ATP and membranes Trace elements are used for metabolic reaction in the cell and cell component stabilization cobalt Co potassium K molybdenum Mo magnesium Mg manganese Mn calcium Ca iron Fe zinc Zn

7. Basic Nutrients for Growth
Organic growth factors such as vitamins, amino acids, and nucleic acids some growth factors cannot be synthesized by own cellular processes Water water activity

8. How Microbes Obtain Nutrients
Heterotroph: uses organic carbon source Autotroph: uses inorganic carbon dioxide Phototroph: uses light as energy source Chemotroph: uses chemical compounds (ie. glucose) Saprobe Parasite

9. Microbial Nutrition Growth Requirements
[INSERT FIGURE 6.1]

10. Culturing Microorganisms
Inoculum introduced into medium (broth or solid)
Environmental specimens
Clinical specimens
Stored specimens
Culture – refers to act of cultivating microorganisms or the microorganisms that are cultivated

11. Culturing Microorganisms
[INSERT TABLE 6.3]

12. Culturing Microorganisms
Special Culture Techniques
Techniques developed for culturing microorganisms
Animal and cell culture
Low-oxygen culture
Enrichment culture

13. Media
Chemically defined Natural Living

14. Media Enriched Media added nutrient encourages
the growth of microorganisms

15. Media Selective Media Selects form a microorganism
while inhibiting most others
Phenol Ethanol Agar
Deoxycholate Agar

16. Media Differential Media Allow for the differentiation of
microorganisms based on
action that occurs on the media
or a color change within the
media that is based on a pH
change
Mannitol Salt Agar
MacConkey Agar

17. Media Question What type of media is Blood Agar considered? Enriched
Selective
Differential

18. The Population Growth Curve
A population of bacteria does not maintain its potential growth rate and double endlessly
A population displays a predictable pattern called a growth curve
The method to observe the population growth pattern:
Place a tiny number of cells in a sterile liquid medium
Incubate this culture over a period of several hours
Sampling the broth at regular intervals during incubation
Plating each sample onto solid media
Counting the number of colonies present after incubation

19. The Rate of Population Growth
Generation or doubling time: The time required for a complete fission cycle
Each new fission cycle or generation increases the population by a factor of 2
As long as the environment is favorable, the doubling effect continues at a constant rate
The length of the generation time- a measure of the growth rate of an organism
Average generation time- 30 to 60 minutes under optimum conditions
Can be as short as 10 to 12 minutes
This growth pattern is termed exponential

20. Stages in the Normal Growth Curve
Data from an entire growth period typically
produce a curve with a series of phases
Lag Phase
Exponential Growth Phase
Stationary Growth Phase
Rapidly Declining Phase
Death Phase

21. Lag Phase Relatively “flat” period
Newly inoculated cells require a period of adjustment, enlargement, and synthesis
The cells are not yet multiplying at their maximum rate
The population of cells is so sparse that the sampling misses them
Length of lag period varies from one population to another

22. Exponential Growth (Logarithmic or log) Phase
When the growth curve increases geometrically
Cells reach the maximum rate of cell division
Will continue as long as cells have adequate nutrients and the environment is favorable
The number of cells growing greatly out number the number of cells dying.

23. Stationary Growth Phase
The population enters a survival mode in which cells stop growing or grow slowly
The rate of cell inhibition or death balances out the rate of multiplication
Depleted nutrients and oxygen
Excretion of organic acids and other biochemical pollutants into the growth medium
The number of cells growing will equal the amount of cells dying.
Endospores begin to form in this phase.

24. Rapidly Declining Phase
The curve dips downward
Cells begin to die at an exponential rate
The amount of cells dying out numbers the amount of cells growing.
The dead cells become nutrients for the growing cells.

25. Death Phase The curve continues to dips downward
Most cellular activity stops
Endospores are formed and released from the parent cells.

26. Phases of Growth Basic phases of growth:
1. Lag phase: new growth medium, period of delay while cells prepare to divide
2. Log phase (exponential growth phase): cellular reproduction most active during this period, generation time reaches a constant minimum
3. Stationary phase: state of equilibrium where number of cell deaths equals number of cell divisions

27. Phases of Growth
Basic phases of growth: 4. Rapidly Declining Phase: cells die logarithmically, endospores formed 5. Death phase: number of deaths exceeds number of new cells

28. Potential Importance of the Growth Curve
Implications in microbial control, infection, food microbiology, and culture technology
Growth patterns in microorganisms can account for the stages of infection
Understanding the stages of cell growth is crucial for working with cultures
In some applications, closed batch culturing is inefficient, and instead, must use a chemostat or continuous culture system

29. Graphing Bacterial Growth
The data from growing bacterial populations are graphed by plotting the number of cells as a function of time
If plotted logarithmically- a straight line
If plotted arithmetically- a constantly curved slope
To calculate thesize of a population over time: Nf = (Ni)2g
Nf is the total number of cells in the population at some point in the growth phase
Ni is the starting number
g denotes the generation number

30. Population Equation
Nf = Ni (2)g