Bacterial growth occurs through binary fission reproduction which doubles the number of bacterial cells over time in a logarithmic fashion. The growth rate varies between bacterial species depending on their optimal conditions. Bacteria require nutrients including carbon, nitrogen, water and inorganic ions for growth as well as environmental factors such as oxygen, temperature, pH and moisture. Bacterial metabolism can involve aerobic respiration, anaerobic respiration or fermentation depending on the oxygen requirements of the bacterial species.

1. Bacterial Growth
Dr. Mohamed alhassan Taha
MBBS-MD Pathology

2. Bacterial Growth
• Definition:
Growth refers to an increase in bacterial cell
number
✓Results from bacterial reproduction.
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Mohamed
alhassan
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3. Bacterial Reproduction
✓Bacteria reproduce a sexually by simple binary
fission.
Elongation of the bacterial cell.
Duplication of the chromosome
Each chromosome attaches to Mesosomes.
Cell membrane and cell wall will form a
transverse septum that divides the mother cell
into 2 equal daughter cells.
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Mohamed
alhassan
Taha
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4. 8/4/2014
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alhassan
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5. Bacterial Reproduction
o The number of bacteria (n) increases
logarithmically.
1 2 4 8 16
❖The doubling (generation) time:
- The time required by the bacteria to double its
number under optimum conditions.
- Varies from one species to another:
E.coli = 20minutes
Mycobacterium tuberculosis = 20 days
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Dr.
Mohamed
alhassan
Taha
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6. Factors affecting the growthof bacteria
• The growth of bacteria needs adequate supply of
nutrients, energy and suitable conditions for the
action of bacterial enzyme
• The growth requirements are:
o Nutrients order to grow bacteria have, e.g.
➢ Oxygen,
➢ Carbon dioxide,
➢ Suitable temperature,
➢ Suitable pH,
➢ Moisture
➢ Others
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Mohamed
alhassan
Taha
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7. Bacteria Nutrition
✓The minimum requirements for growth include:
water; a source of carbon; a source of nitrogen;
and certain inorganic salts.
- Nitrogen is required for synthesis of DNA; RNA and
ATP
- Sulphur is required for synthesis of amino acids and
vitamins;
- Inorganic ions; Na; K; Mg; Fe; Ca are required to
facilitate enzymatic catalysis and to maintain
chemical gradient across the cell membrane.
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Dr.
Mohamed
alhassan
Taha
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8. Bacteria Nutrition
oBacteria are classified into:
1-Heterotrophic bacteria:
(hetro= other)
- Use preformed organic compounds (made by
others) for their growth.
2- Autotrophic bacteria:
(auto= self)
- They utilize simple inorganic compounds to
produce complex organic substances like CO2
and ammonium salts.
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Mohamed
alhassan
Taha
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9. Most bacteria of medical importance
are heterotrophic

10. • According to oxygen requirements ; bacteria are
classified into
1. Obligatory aerobes
2. Obligatory anaerobes
3. Facultative aerobes
4. Microaerophilic
5. Aerotolerant
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alhassan
Taha
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alhassan
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1.Obligatory aerobes:
Grow only in the presence of oxygen; e.g
Mycobacterium tuberculosis
2. Obligatory anaerobes:
Grow only in the absence of oxygen
3. Facultative anaerobes:
Grow in the presence or absence of oxygen

12. 4. Microaerophilic bacteria:
Grow best in lower amount of oxygen
E.g.: Campylobacter and Helicobacter bacteria
5. Aerotolerant bacteria:
Are anaerobic ; but can tolerate the presence of
oxygen
E.g: Clostridium perfringes
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Mohamed
alhassan
Taha
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13. • The use of oxygen by bacteria generates toxic
products such as superoxide and hydrogen
peroxide.
• Aerobes and facultative bacteria have enzymes; such as
superoxide dismutase and catalase that detoxify these
products, but anerobes lack these enzymes and they are
killed in presence of oxygen
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Mohamed
alhassan
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14. • Most bacteria require CO2 in low concentration.
• Certain bacterial species) require higher
concentrations of CO2 (Capnophilic(, e.g.:
- Neisseria species require 5-10%.
- Brucella abortus require 20% CO2.
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Mohamed
alhassan
Taha
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CO2

15. Temperature
• Different microbial species vary widely in their
optimal temperature ranges for growth:
✓ Psychrophilic:
grow best at low temp (15 -20°C)
✓ Mesophilic:
grow best at 25 - 40° C.
✓ Thermophilic :
grow best at 50 - 80°C
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Mohamed
alhassan
Taha
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16. Temperature
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alhassan
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17. Most of Medically Important
Bacteria are Mesophilic

18. Hydrogen ion concentration (pH)
✓Most bacteria of medical importance can grow at
a pH of 6-8 (neutralophiles).
• Some bacterial species require acidic pH for their
growth (acidophiles) ,e.g lactobacilli. In female
vagina
• Others require alkaline pH (alkaliphiles) ,e.g.
Vibrio cholerae.
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alhassan
Taha
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19. Light
✓ Phototrophs= derived energy from sunlight
✓ Chemotrophs= derived energy from chemicals
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alhassan
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20. • Four-fifth of bacteria cell weight consists of
water, and moist is necessary for growth.
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alhassan
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Moisture

21. ✓Fastidious bacteria:
are those which require unusually complex
nutrients for growth.
E.g. Hemophilus influenzae
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Mohamed
alhassan
Taha
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alhassan
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Mohamed
alhassan
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24. Bacterial Growth Curve
• If a small number of bacteria are inoculated into a
liquid nutrient medium and the bacteria are
counted at frequent intervals and the results
plotted, a characteristic growth curve with four
phases is obtained:
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alhassan
Taha
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25. BacterialGrowthCurve
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Mohamed
alhassan
Taha
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26. Bacterial Growth Curve
1- Lag Phase:
- No cell division.
- The bacteria form the enzymes and molecules
needed for replication
✓Correlates with the incubation period in vivo.
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Mohamed
alhassan
Taha
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27. Bacterial Growth Curve
2- Logarithmic (exponential) phase:
- Rapid cell division occurs.
- The number of living bacteria increases by time.
✓This phase correlates with symptoms and signs of
the disease.
✓ Antibiotics are most effective at this stage.
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Mohamed
alhassan
Taha
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28. 3- Stationary phase:
- Nutrients are exhausted.
- Waste products are accumulated.
- The number of dying cells = number of new
cells
- (The number of living bacteria remains
constant).
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Mohamed
alhassan
Taha
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29. 4- Death (Decline) Phase:
- Nutrients are more exhausted.
- Waste products are more accumulated.
- The number of dying cells > number of new
cells.
- The number of living bacteria decreases by
time.
o Correlates with recovery and convalescence.
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Mohamed
alhassan
Taha
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30. Bacterial Metabolism
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alhassan
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31. BacterialMetabolism
• Bacterial metabolism is the sum of anabolic
processes (synthesis of cellular constituent
requiring energy) and catabolic processes(break
down of cellular constituents with concomitant
release of waste products and energy rich
compounds.
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alhassan
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32. • Bacterial metabolism can be categorized in to :
(1) Aerobic respiration:
- Occurs through glycolysis.
- Produce 38 ATP
- The final hydrogen recipient is the oxygen.
- Results in formation of hydrogen peroxide and
Super oxide; which are toxic.
- Is used with the aerobic and facultative
anerobic bacteria.
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Mohamed
alhassan
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33. (2)Anaerobic respiration:
• Occurs in absence of oxygen.
• Occurs through glycolysis and Krebs cycle.
• The final electron receptor is nitrate; sulfate; or
CO2
• Yields less energy
• Used by anerobic bacteria because the lack
catalase and superoxide dismutase enzymes.
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Mohamed
alhassan
Taha
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34. (3) Fermentation:
- Refers to the break down of sugar in absence of
oxygen) to pyruvic acid and produces 2ATP
directly.
- It is the process by which facultative bacteria
generate ATP in absence of oxygen.
✓The fermentation of certain sugars is the basis
of the laboratory diagnosis of some bacteria.
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Mohamed
alhassan
Taha
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