 Bacteria
reproduce by binary fission, a process by
which one parent cell divides to form two progeny
cells.
 One
cell gives rise to two progeny cells two to four
and so forth.
 This
type of growth is called exponential growth or
logarithmic growth.
 It
is expressed as
 No
of bacteria. 2, 4, 8, 16
Expopnent
. 20,22,23.24
 Thus,
1 bacterium will produce 16 bacteria after 4
generations.
 The
doubling (generation) time of bacteria is the
time in which bacteria double their number.
 It
ranges from as little as 20 minutes for
Escherichia coli to more than 24 hours for
Mycobacterium tuberculosis.


1.
2.
3.
The Growth Cycle of bacteria:
It has four major phases.
The first is the lag phase, during which enormous
metabolic activity occurs but cells do not divide.
This can last for a few minutes up to many
hours.
The log (logarithmic) phase is when rapid cell
division occurs.
The stationary phase occurs when nutrient
depletion or toxic products cause growth to slow
until the number of new cells produced balances
the number of cells that die resulting in a steady
state.
4.
The final phase is the death phase, in which
there is a decline in the number of bacteria.

The essential factors required for the growth of
bacteria in vitro are.
1. Nutrients
2. Temperature
3. Oxygen concentration
4. Organic growth factors
5. PH
1.
Nutrients:

Important factor to carry out metabolic activity. On
the basis of nutritional requirement they are
a.
Heterotrophs. Those get preformed nutrients like
sugar, amino acids.
b.
Autotrophs. Those synthesize their own
nutrients.
2.
Temperature:

The optimum temp for growth is 36.50C (the
body temp range is 35-420C).

Certain bacteria can grow at refrigeration
temperatures i.e.0-50C.
 On
basis of temperature requirements bacteria can
be divided into.
a.
Psychrophiles (cold temp loving) e.g. Salmonella,
Staphylococci, Proteus etc.
b.
Mesophiles ( moderate temp loving)
c.
Thermophiles ( heat loving).
3.
Oxygen requirements:
 For
most organisms, an adequate supply of oxygen
enhances metabolism and growth.
 The
use of oxygen generates two toxic molecules,
hydrogen peroxide (H2O2) and the free radical
superoxide (O2).
 Bacteria
require two enzymes to remove these
radicals. The first is superoxide dismutase, which
catalyzes the reaction

2O.2 + 2H _____ H2O2 + O2
 Second
 2H2O2
is catalase, which catalyzes the reaction
_____ 2H2O + O2

On the basis of oxygen requirement bacteria can
be classified into.
1.
Obligate aerobes e.g. M.tuberculosis,
P.aeruginosa
2.
Facultative anaerobes e.g. Staphylococci,
Streptococci, enteric bacilli
3.
Obligate anaerobes e.g. Clostridium spp.
4.
Organic Growth Factors:
 Essential
organic compounds which an organism is
unable to synthesize are known as organic growth
factors.
 They
must be directly obtained from the
environment.
 One
group of organic growth factors for humans is
vitamins.
 Many
bacteria can synthesize their own
vitamins and do not depend on outside sources.
 However,
some bacteria lack the enzymes needed
for the synthesis of certain vitamins, and for them
those vitamins are organic growth factors.
 Other
organic growth factors required by some
bacteria are amino acids, purines, and pyrimidines.
5.
PH:
 Most
bacteria grow best in a narrow pH range near
neutrality, between pH 6.5 and 7.5.