1. Bacterial Metabolism @ Bacteria break down and utilize food
stuffs through certain metabolic
pathways.
Catabolism:
@ Food is broken down and energy is liberated.
Anabolism:
@ Polymers are built up, e.g. proteins,
polysaccharides, fat

3. Chemical Composition of Bacteria
Principal chemical components of bacteria :
1 – High mol.wt.organic compounds: form 80%
of cell dry wt.e.g: proteins, nucleic acids,
carbohydrates, lipids.
2 –Low mol.wt.organic compounds: form 10 %
of cell dry wt.e.g: co-enzymes, other
growth factors.
3-Inorganic compounds: form 10 % of cell dry
wt. e.g. water, mineral salts (P, SO4, Na,
K, etc).

5. Sources of Chemical Elements (1)
1- H + O: from water
2- C: a) from air carbon dioxide taken by
non-parasitic bacteria (autotrophs).
Energy is obtained by oxidation of
inorganic compounds (chemosynthetic
autotrophs) or from sunlight (photo-
synthetic autotrophs).
b) From organic compounds taken by
parasitic bacteria (organotrophs).
Energy obtained by breakdown of the
organic carbon sources.

7. Sources of Chemical Elements (2)
3-Nitrogen:Taken from ammonium salts,
aminoacids, and nucleotides
4 -Inorganic salts: Taken from medium or
environment, e.g: anions (phosphates,
sulphates) & cations (Na, K, Mg, Mn, Ca)
5- Growth factors: Synthesized by the
organism, or added to medium. Function
as catalysts for growth. Include: thiamine,
riboflavin, nicotinic acid, PABA, folic
acid, biotin, pyridoxine, etc .

9. Growth Physical Factors (1)
1- Oxygen:
* Facultative anaerobes (grow in presence
and absence of air), e.g: Staph, Strep.
* Strict (obligate) aerobes (grow in air
only), e.g. Mycobacteria, Pseudomonas.
* Strict (obligate) anaerobes (grow in
absence of air), e.g: Clostridia.
* Microaerophilic (grow in small traces of
oxygen, and increased concentration
of carbon dioxide), e.g: Neisseria.

11. Growth Physical Factors (2)
2- Carbon dioxide:
Bacteria obtain carbon dioxide from air
and oxidation and fermentation reactions
3- Temperature:
Optimum temp. for pathogens is 37°C.
Soil bacteria: 25°- 40°C.
A-Mesophiles: 25º-40º C.
B-Psychrophiles: below 20° C (0°- 7°c).
C-Thermophiles: 55°-80º C.
4- Moisture:
Dryness kills most bacteria, e.g: G.C,
Some resist dryness, e.g: Clostridia

13. Growth Physical Factors (3)
5 - Hydrogen-ion Concentration (pH):
Optimum pH is Lactobacilli need
acid pH. Vibrios need alkaline pH
6 – Light & Radiation:
Darkness is the best. Mycobacteria resist
light. U.V & infra­red destroy bacteria.
7- Osmotic Pressure:
5-15 % Na Cl concentration is optimum.
Halophilic bacteria need 25 % Na Cl conc.
8- Mechanical & Sonic Trauma:
Bacteria are destroyed by long shaking,
long centrifugation, & vibration.

15. Metabolism (1) @ Bacteria use enzymes to break down food:
proteases, polysaccharidases, lipases, etc
@ Net: amino-acids, sugars, fatty acids.
@ Carbohydrates are broken by:
a-Embden-Meyerhof pathway – glycolysis
b-Krebs cycle or citric acid cycle.
c-Hexose monophosphate shunt
d-Phosphoketolose pathway.
e- Entner- Doudoroff pathway.

17. Metabolism (2) @ Breakdown of lipids is through oxidation of
fatty acids.
@ Breakdown of protein through deamination
transamination, & decarboxylation.
@ Bacteria need the following to synthasize
macromolecules (anabolism):
1- Supply of low mol.wt. compounds (sugars,
amino-acids, fatty acids, etc)
2-Source of energy (ATP)

19. Modes of Energy Yield 1- Fermentation:.
Organic compounds serve both as electron
donor and electron acceptor. Made by
anaerobes. Gives lactic,acetic,formic acids
2-Respiration: divided into:
a-Aerobic: oxygen serves as electron
acceptor.Process is oxidation-reduction.
b-Anaerobic: inorganic salts (sulphates,
nitrates) serve as electron acceptor
3- Photosynthesis: Photosynthetic bacteria
pigments converts light energy to ATP.