1. Bacterial growth Assist. Prof. Emrah Ruh NEU Faculty of Medicine
Department of Medical Microbiology

2. Bacterial growth Microbial growth: Growth rate:
Increase in the number of microbial cells in a population
Growth rate:
The change in cell number or cell mass per unit time
During the cell division cycle, all the structural components of the cell double

3. Bacterial growth Generation: Generation time (doubling time):
The interval for the formation of two cells from one cell
Generation time (doubling time):
The time required for the cell population to double
Vary widely among organisms (many bacteria: 1-3 hr; few bacteria: 10 min or several days!)

4. Bacterial growth The requirements: Physical Chemical
Temperature, pH, salt
Chemical
Carbon, nitrogen, oxygen

5. Bacterial growth Physical requirements – Temperature
Psychrophiles: can grow at 0°C but optimum is about 15°C
Psychotrophs: can grow at 0°C also but optimum is °C
Mesophiles: grow best at moderate around 37°C (many pathogenic microorganisms)
Thermophiles: have a growth optimum at around 60°C
Hyperthermophiles: have growth optimum of 80°C or higher (archaea)

6. Bacterial growth Physical requirements – Temperature

7. Bacterial growth Physical requirements – Temperature

8. Bacterial growth Physical requirements – Temperature
Effect of temperature on growth rate and the molecular consequences for the cell

9. Bacterial growth Physical requirements – pH
Most bacteria grow best at pH value between 6.5 and 7.5
Acidophiles: organisms that grow best at low pH (as low as pH 1)
Alkaliphiles: organisms that grow best at high pH (as high as pH 10) (archaebacteria)

10. Bacterial growth Physical requirements – Salt
In a hypertonic solution, most microbes undergo plasmolysis
Isotonic
Hypertonic

11. Bacterial growth Physical requirements – Salt
Halophiles: specific requirement for the sodium ion (microorganisms found in the sea)
Mild halophile  1-6% NaCl
Moderate halophile  6-15% NaCl
Extreme halophile  15-30% NaCl (archaebacteria)
Halotolerant: grow best in the absence of NaCl, but can tolerate some NaCl

12. Bacterial growth Physical requirements
Osmophiles: are able to live in environments high in sugar
Xerophiles: are able to grow in very dry environments

13. Bacterial growth Chemical requirements
Macronutrients
Micronutrients (trace elements)
Growth factors

14. Bacterial growth Chemical requirements
Macronutrients
Required in large amounts
Micronutrients (trace elements)
Required in tiny (trace) amounts
Metals; enzyme structure

15. Bacterial growth Chemical requirements
Growth factors (organic compounds)
Vitamins, amino acids, purines and pyrimidines
Required in tiny amounts; only by some bacteria
Most microorganisms are able to synthesize all of these compounds; some microorganisms require one or more of them performed from the environment
Vitamins are the most commonly needed growth factors

16. Bacterial growth Chemical requirements
Macronutrients
Micronutrients
Vitamins
Carbon (C)
Chromium (Cr)
p-Aminobenzoic acid
Hydrogen (H)
Cobalt (Co)
Folic acid
Oxygen (O)
Copper (Cu)
Biotin
Nitrogen (N)
Manganese (Mn)
Cobalamin
Phosphorus (P)
Molybdenum (Mn)
Lipoic acid
Sulfur (S)
Nickel (Ni)
Nicotinic acid (niacin)
Potassium (P)
Selenium (Se)
Pantothenic acid
Magnesium (Mg)
Tungsten (Tu)
Riboflavin
Sodium (Na)
Vanadium (V)
Thiamine
Calcium (Ca)
Zinc (Zn)
Vitamins (B6)
Iron (Fe)
Vitamin K group; quinones
Hydroxamates

17. Bacterial growth Chemical requirements – Carbon
The major element in all classes of macromolecules
A typical cell is about 50% carbon
All organisms require a carbon source; chemoheterotrophs use an organic molecule and autotrophs typically use carbon dioxide

18. Bacterial growth Chemical requirements – Nitrogen
A typical bacterial cell is about 12% nitrogen
Important element in proteins, nucleic acids,...
Bacteria obtain nitrogen from ammonia (NH3) or nitrate (NO3-); a few bacteria (nitrogen-fixing bacteria) obtain from nitrogen gas (N2)

19. Bacterial growth Chemical requirements – Oxygen
Oxygen requirement:
Obligate aerobes
Microaerophiles
Facultative anaerobes
Aerotolerant anaerobes
Obligate anaerobes
Requirement for oxygen

20. Bacterial growth Chemical requirements – Oxygen

21. Bacterial growth Chemical requirements – Oxygen
Aerobic bacteria: grow on the top of the tube in order to absorb maximal amount of O2 for survival.
Microaerophilic bacteria: grow just below surface as they require O2 at low concentration. They are sensitive to O2 -derived free radicals.
Facultative anaerobic bacteria: grow throughout the tube. These bacteria can use O2. But in the absence of O2, they have anaerobic methods of energy production, so they can live all along the test tube.

22. Bacterial growth Chemical requirements – Oxygen
Aerotolerant anaerobic bacteria: cannot use O2 for growth but also are not affected by it and able to survive in the presence of some O2. So, they can spread a little bit upward from the bottom of the test tube.
Anaerobic bacteria: cannot use O2 for growth and are even harmed by it. So, they grow at the bottom in order to avoid O2.

23. Bacterial growth Chemical requirements – Oxygen
Aerobes, facultative anaerobes, and aerotolerant anaerobes must have the following enzymes to avoid toxic O2 radicals:
Superoxide dismutase (2O2- + 2H O2 + H2O2)
Catalase (2H2O H2O + O2) or peroxidase (H2O2 + 2H H2O)

24. Bacterial growth Media
Medium: is any material prepared for the growth of bacteria in a laboratory
Culture: Microbes that grow and multiply in a medium

25. Bacterial growth Media
Media used in microbiology labs are divided into four groups according to their agar content
Agar is a biological substance extracted from sea algae
Agar solidifies the media
> 90oC: liquid phase
< 40oC: solid phase

26. Bacterial growth Media
Liquid media; do not include agar
Semi-liquid media; include 0,05-0,2 % agar
Semi-solid media; include 0,3-0,5 % agar
Solid media; include 1,5-2 % agar

27. Bacterial growth Media
Liquid
medium
Semi-liquid
medium
Semi-solid
medium
Solid
medium

28. Bacterial growth Media
Bacterial growth in solid culture is observed as colony formation
Colony

29. Bacterial growth Media
Bacterial growth in liquid culture is observed as turbidity
Turbidity
Medium (no bacteria)
Culture (bacteria)

30. Bacterial growth Measurement of bacterial growth
Counts are reported as the number of colony- forming units (CFU) instead of the number of cells
If the concentration of bacteria is too great, the colonies will grow into each other and the plate will be uncountable
To insure a countable culture plate, a series of dilutions should be prepared

31. Bacterial growth Measurement of bacterial growth
Plate no. 4  32 colonies X 10,000 = 320,000 cfu/ml

32. Bacterial growth Media - Ingredients
Simple growth requirements:
Nutrient broth ( + agar: Nutrient agar)
Constituent
Peptone (provides vitamins and minerals)
Beef extract (supplies energy, C, N and S)
Sodium chloride
Agar
Water

33. Bacterial growth Media – General purpose media
Simple growth requirements
Nutrient broth
Nutrient agar

34. Bacterial growth Media – General purpose media
Simple growth requirements + blood: Blood agar
The most common media in microbiology!

35. Bacterial growth Media – Special purpose media
Selective media: supress unwanted microbes; encourage desired microbes
Differential media: differentiate the colonies of desired microbes from others
Enrichment media: increase the numbers of desired microbes to detectable levels

36. Bacterial growth Media – Special purpose media
Endo agar, EMB agar and MacConkey agar: Selective and differentiative media
Selective for Gram-negative bacteria (suppress Gram-positive bacteria)
Differentiative for lactose-fermenting bacteria (Lactose (+) bacteria produce colourful colonies)

37. Bacterial growth Media – Special purpose media
Lactose fermentation test
Lactose (+) bacteria
produce
colourful colonies

38. Bacterial growth Bacterial division
Binary fission:
The normal reproductive method of bacteria
A single cell divides into two identical cells

39. Bacterial growth Bacterial division

40. Bacterial growth Logarithmic representation
Logarithmic representation of bacterial populations:
Bacterial division occurs according to a logarithmic progression (two cells, four cells, eight cells,...)

41. Bacterial growth Logarithmic representation
Logarithmic representation of bacterial populations:

42. Bacterial growth Phases of growth
Lag phase
Log (exponential) phase
Stationary phase
Death phase

43. Bacterial growth Phases of growth

44. Bacterial growth Phases of growth
Lag phase:
No change in the number of cells; metabolic activity is high
DNA and enzyme synthesis occurs

45. Bacterial growth Phases of growth
Log (exponential) phase:
Bacteria multiply at the fastest rate (under the optimal conditions)
Logarithmic or exponential increase in population

46. Bacterial growth Phases of growth
Stationary phase:
Equilibrium between cell division and death
Nutrients are exhausted and waste products build up; pH increases

47. Bacterial growth Phases of growth
Death phase:
The number of deaths exceeds the number of new cells formed
Population decreases at a logarithmic rate