1. Growth requirements of bacteria& growth curve
L. Dalia Kamal Eldien
MSc in Microbiology
Lecture NO: 4

2. Questions for revision the previous lecture
What the different between bacteria& blue green algae?
Name the types of bacteria according to morphological classification
Write the principle of Gram stain
What the different between Gram positive& Gram negative cell wall?

3. Outlines At the end of this lecture, the student should know:-
Factors affect bacterial growth
Bacterial growth curve
Cultivation of bacteria
Theory of bacteria growth& multiplication

4. Introduction
All cells must accomplish certain metabolic tasks to grow and divide.
Bacteria need physical & chemical factors to grow

5. Factors affect bacterial growth (Growth Requirements)
Nutrition
Temperature
Oxygen
Carbon dioxide
Moisture and drying
Light pH
Osmotic pressure

6. Nutrition factors
All bacteria have three major nutritional needs for growth:
A source of carbon (for making cellular constituents). Carbon represents 50% of the dry weight of a bacterium.
A source of nitrogen (for making proteins). Nitrogen makes up 14% of the dry weight.
A source of energy (adenosine triphosphate [ATP], for performing cellular functions).
Smaller amounts of molecules, such as phosphate for nucleic acids and phospholipids of cell membranes and sulfur for protein synthesis, make up an additional 4% of the weight.

7. Nutrition factors
Various metals and ions for enzymatic activity must also be present. Important mineral ions, such as Na+, K+, Cl−, and Ca2+, are also required.
Although the basic building blocks required for growth are the same for all cells, bacteria vary widely in their ability to use different sources of these molecules

8. Nutrition factors
Bacteria are classified into two basic groups according to how they meet their nutritional needs.
Autotrophs , are able to grow simply, using carbon dioxide as the sole source of carbon, with only water and inorganic salts required in addition.
Heterotrophs, requires more complex substances for growth. These bacteria require an organic source of carbon, such as glucose, and obtain energy by oxidizing or fermenting organic substances.
Autotrophs occur in environment, while all bacteria that inhabit the human body are heterotrophic

9. Temperature
Generally, an increase in temperature will increase enzyme activity.
But if temperatures get too high, enzyme activity will diminish and the protein will denature.
Lowering temperature will decrease enzyme activity.
At freezing temperatures enzyme activity can stop
Every bacterial species has specific growth temperature of its enzymes:
Minimum growth temperature
Optimum growth temperature
Maximum growth temperature

10. Temperature Bacteria can be classified on the basis of temperature
Thermophilic: high-temperature-loving microorganism, with growth optimum growth temperature above45°C
Mesophilic: a microorganism, that lives at moderate temperature grow best at 30-37°C temperatures - many pathogens fall in this category.
Psychrophilic: Cold-temperature-loving, tolerant microorganism, optimum growth temperature blew20°C

11. Oxygen
Differences in the effect of oxygen on bacterial growth provide a further way of classifying bacteria:
Obligate aerobes:-
Bacteria which require free oxygen to grow
Obligate anaerobes:
Bacteria which are unable to grow in free oxygen

12. Oxygen factor 3. Facultative anaerobes:-
Bacteria which can grow in conditions in which oxygen is present or absent
4. Microaerophilic:-
Bacteria which grow best in conditions of reduced oxygen concentration.

13. Carbon dioxide factor
All bacteria require small amounts of carbon dioxide for growth.
This requirement is usually met by the carbon dioxide present in the atmosphere.
Some bacteria like Brucella abortus require much higher levels of carbon dioxide, known as carboxyphilic

14. Moisture& drying factor
Water is an essential ingredient of bacterial protoplasm and hence drying is lethal to cells.
The effect of drying varies in different species.

15. pH Some bacteria grow at acidic PH (3-6), known as: acidophilic.
Or grow at alkaline PH (8-10), known as: alkelophilic /basophilic.
Most bacteria grow at neutral PH (7)

16. Osmotic pressure Bacteria vary in their tolerance to salt levels
Some cannot tolerate high concentration of salt
Some tolerate medium concentration of salt.
Some can tolerate high concentration of salt, called: halophilic.

17. Growth& multiplication of bacteria
Bacteria reproduce by binary fission and cell divides to form two daughter cells.
Nuclear division precedes cell division and therefore, in a growing population, many cells having two nuclear bodies can be seen.
Bacterial growth may be considered as two levels, increase in the size of individual cells and increase in number of cells.

18. Binary fission

19. Bacterial growth curve
No growth will occur without the presence of at least one viable cell
When bacteria is grown in a suitable broth medium and incubated its growth follows a definite process.
After inoculation and plotted in relation to time, a growth curve is obtained.

20. Broth media

21. Growth curve The curve shows the following phase :-
Lag phase: adaptation of bacteria to environment
Log phase: microorganisms are growing and dividing at the maximal rate
Stationary phase: number of new equal to number of death
Decline phase: In this phase there is progressive death of cells

22. Bacterial curve

23. Identify the different phases A, B, C& D in bacterial growth curve

25. Cultivation of bacteria
The purpose of using cultural techniques in microbiology is to demonstrate the presence of organisms which may be causing disease, and when indicated, to test the susceptibility of pathogens to antimicrobial agents.
Thus, development of synthetic culture media and culture techniques have played important roles in the advancement of this field.
Microbiologists use bacterial culture media for many purposes and applications.
Culture media can be solid or broth (fluid) or semi solid

26. Broth media

27. Solid culture media

28. How to culture bacteria in the lab

29. How to culture bacteria in the lab

30. Bacteria grow on media plate

31. Bacteria grow on media plate

32. Sources
District Laboratory Practice in Tropical Countries, Part 2 (chapter 7)
Lippincott's Illustrated Reviews: Microbiology, 3rd Edition (2012)- Richard A. Harvey- Bruce D. Fisher- Richard A. Harvey-(chapter6)