all details about the bacterial nutrition

1. BACTERIALNUTRITION AND FACTORS AFFECTINGGROWTH
 The principal constituent of bacterial cell is water, which is about 80% of the total weight.
For growth of bacteria-
 The minimum nutritional requirement is water
A source of carbon,
A source of nitrogen and some inorganic salts.
 These nutritional elements may be supplied in suitable artificial culture media.
 In addition to these, bacteria require sulphur, phosphorus and other elements-
such as sodium, potassium, magnesium, iron and manganese in small amounts.
 Some bacteria may require some special nutrients to be incorporated in the culture media.
ENVIRONMENTAL FACTORS AFFECTING GROWTH
1. Moisture and Desiccation
 Moisture is an essential requirement for the growth of bacteria because 80% of the bacterial cell
consists of water.
 However, the drying has varying effects in different organisms.
 Some organisms like Treponema pallidum and N gonorrhoeae die quickly after drying
 While M. tuberculosis and Staph. aureus may survive drying for several weeks.
 Drying in cold and vacuum (lyophilisation or freeze drying) is used for preservation of
microorganisms.
Clinical Significance:-
 Lyophilisation is an important method of preservation of microorganisms and many biological
materials such as vaccines, antibiotics etc.
2. Oxygen
On the basis of requirement of oxygen , bacteria aredivided into:-
 Aerobes.
 Anaerobes.
(a) Aerobes:- They require oxygen for their growth.
obligate aerobes:- which grow only in the presence of oxygen.
Eg:- Pseudomonas aeruginosa

2. facultative anaerobes:- that are ordinarily aerobes but can also grow without oxygen.
Most ofthe pathogenic bacteria are facultative anaerobes.
Microaerophilic bacteri a (microaerophiles) can grow in the presence of traces of oxygen.
Eg:- Campylobacter and Helicobacter pylori.
(b) Anaerobes:
The obligate or strict anaerobes can grow only in the absence of oxygen.
Eg:-Clostridium tetani
Obligate anaerobes cannot grow even in the presence of traces of oxygen.
3. Carbon Dioxide
Brucella abortus require much higher level of carbon dioxide (5-10 per cent) for their growth , especially for
primary isolation. These bacteria are called capnophilic bacteria.
4. Temperature
The temperature at which growth occurs best , is known as the optimum temperature.
On the basis of optimum temperature range for growth, bacteria are grouped as follows:-
(a) Mesophiles - between 25°C and 40°C
e.g. majority of the pathogenic bacteria.
(b) Psychrophiles - below 20°C
e.g. soil and water saprophytes.
(c) Thermophiles - between 55°C and 80°C
e.g.Geobacillus stearothermophilus (formerly Bacilluss tearothermophilus).
Clinical Significance
Most of the pathogenic bacteria die between 55°C to 65°C and most spores between 100°C to 120°C.
5.pH
Most of the medically important bacteria can grow at pH 7.2-7 .6.
However, some bacteria such as lactobacilli and vibrio cholerae grow at acidic and alkaline pH respectively.
Strong solutions of acid or alkali (5 % hydrochloric acid or sodium hydroxide) kill most bacteria but
mycobacteria are resistant to these agents.

3. Clinical Significance
Culture media having alkaline pH are used for growing Vibrio cholera.
6. Light
Bacteria (except phototrophic species) grow wellin darkness.
They are sensitive to ultraviolet rays and other radiations.
Photochromogenic mycobacteria produce pigment only on exposure to light.
7. Osmotic Effect
8. Mechanical and Sonic Stresses
Though bacteria have tough cell walls, they may be ruptured and disintegrated by vigorous shaking with glass
beads and by exposure to ultrasonic vibrations.