1. Microbial Growth 1

2. Bacterial cell is composed of :
Water
Organic
Protein
Sugars
Lipids
Nucleic acid

3. Microbial nutrition proteins, carbohydrates
Macronutrients – required in large quantities; play principal roles in cell structure & metabolism
proteins, carbohydrates
Micronutrients or trace elements – required in small amounts; involved in enzyme function & maintenance of protein structure
manganese, zinc, nickel 3

4. Bacterial Nutrition and Growth
Classification based on their source of carbon
1. Autotrophs
2. Heterotrophs :saprophytes ; parasites 4

5. Bacterial Nutrional Modes5

6. Requirements for Microbial Growth
Physical Requirements
Chemical Requirements 6

7. The Requirements for Growth
The requirements for microbial growth can be divided into two main categories:
physical and chemical.
Physical aspects include
temperature, pH, and osmotic pressure.
Chemical requirements
include sources of carbon, nitrogen, sulfur, phosphorus, oxygen, trace elements, and organic growth factors. 7

8. Temperature
Optimum temperature – promotes the fastest rate of growth and metabolism
Mesophilic forms （30-37C ℃）include all human pathogens and opportunists. pH
Many grow best at neutral pH (Most bacteria grow in the range of pH 8

9. Requirements for Microbial Growth Physical requirements
The composition of bacterial cell is 80-90% water.
3- Osmotic Pressure
In high osmotic pressures solution (hypertonic), the water move from inside bacterial cell to outside
The growth of the cell is inhibited as the plasma membrane pulls away from the cell wall.
Thus, addition of salts or other solutes to solution can be used to preserve food.
Loss of water from the cell results in Plasmolysis. 9

10. 10

11. Oxygen Requirements 11

12. for growth Required CO2
N. meningitidis
N. Gonorrhoeae 12

13. Requirements for Microbial Growth chemical requirements
# Carbon:
Chemoheterotrophs: organic matter
Chemooutotrophs , photoutotrophs from Co2.
# Nitrogen _Sulfur _and phosphorous
# Trace Elements: iron _ copper _ and zinc
# Oxygen: 13

14. Bacterial growth
&
reproduction

15. Binary fission in bacteria15

16. Bacterial culture

17. Culture media
Any material prepared in the laboratory for the growth of bacteria and usually in test tubes or petri dishes
Culture = microbes that grow & multiply in or on a culture medium

18. Types of culture media Agar;
Culture medium
Inoculum
Culture
Sterile
Types of culture media
Solid (agar)/semisolid/liquid (broth)
Agar;
liquid down to 50C solidify at 45 C, not consumed by bacteria as nutrient.
Agar solid media are poured in plates(Petri dish) or tubes. In tubes they are poured either as slants or deeps. 18

19. Culture media
Chemically defined media = is one in which the exact chemical composition is known (energy source , carbon , nitrogen , sulfur , phosphorus , growth factors)
Complex media = in which the exact chemical composition varies slightly from batch to batch (protein added)

20. Culture media
Differential media = used to distinguish among different kinds of bacteria

21. Culture media
Selective media = allow the growth of only one kind of bacteria & prevent the growth of other by the addition f certain salts & dyes

22. Culture media
Enrichment media = is used to encourage the growth of particular bacteria in mixed culture

23. Obtaining pure culture

24. Streak-Plate Method 24

25. Inoculated culture media must be incubated at 37C = incubator
*some bacteria require an increased CO2 concentration = CO2 incubator or candle jars can be used
*some bacteria need anaerobic condition to grow ( remove O2)

26. Bacterial colonies on several differential media. 26

27. The Growth of Bacterial Cultures
Binary fission
Generation time
Phases of Growth 27

28. Growth curve
Lag phase – “flat” period of adjustment, enlargement; little growth
Exponential growth phase – a period of maximum growth will continue as long as cells have adequate nutrients & a favorable environment
Stationary phase – rate of cell growth equals rate of cell death cause by depleted nutrients & O2, excretion of organic acids & pollutants
Death phase – as limiting factors intensify, cells die exponentially in their own wastes 28

29. Generation time time for bacterial mass to double Example
100 bacteria present at time 0
If generation time is 2 hr
After 8 hr mass = 100 x 24 29 29 29

30. Obtaining Pure Culture
Colony=is a visible mass of microbial cell that theoretically arose from one cell
Streak plate technique 30

31. The streak plate method for isolating pure bacterial cultures. 31

32. First Term Exam.
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