Transcript What are bacteria?

Bacterial
culture
Introduction
What are bacteria?







Prokaryotic organism
Unicellular
No nuclear envelope around the genomic
DNA
Absence of cellular organites
1-10 μm
Variable shapes (round, stick ...)
May be pathogenic
What are bacteria?
Bacterial division

Multiplication by binary fission:
bacteria grows and divides into
identical daughter cells.
the
two

Preceded by duplication of the bacterial
chromosome with the DNA replication.

Various
synthesis
and
degradation
enzymatic systems involved in the cell
division.
Bacterial division
Bacterial growth

Growth of all the components of the
bacteria which leads to increasing the
number of bacteria

Characterized by a generation time (G)
variable depending on the species
20 minutes for Escherichia coli, Lactobacillus acidophilus for
100 minutes, 1000 minutes to Mycobacterium tuberculosis

Depends on physical and chemical
parameters such as pH, temperature, the
presence of O2, CO2, water availability .
Bacterial growth
After n cycles : 2n bactéria
Bacterial growth
For example, Escherichia coli
G= 20 minutes







After
After
After
After
After
…
After
1
2
3
4
5
hour: 3 cycles : n = 23 = 8 bacteria
hours: 6 cycles : n = 26 = 64 bacteria
hours : 9 cycles : n = 29 = 512 bacteria
hours : 12 cycles: n = 212 = 4096 bacteria
hours : 15 cycles: n = 215 = 32768 bacteria
10 hours : 30 cycles : n = 230 = 1073741824 bacteria
More than a billion bacteria
after 10 hours of culture!
Bacterial growth

In liquid culture media :
Bacteria
Increasing the cell density during the
growth
Clear media
After 16h of
culture =
turbid media
Bacterial growth

In solid culture media :
Bacteria
Accumulation of cells during the
growth
After 16 - 24h :
1 bacteria  1 visible bacterial
colony
Bacterial
culture
Different culture media
Different cuture media

Solid by adding a
gelling agent (agar) to
a liquid media

Liquid
Different culture media
depending on their use
The isolation and identification media
Basal media =
all common
bacteria culture
Selective media
= Contains a
selective agent
promoting the
culture of an
exclusive family
of microorganism
Identification media
= Used to characterize bacteria
with differential colorimetric
tests
Different culture media
depending on their use
Different
media
Agar plate
media
packaging
of
identification
Tubes media
Classics
tubes
Multi-test
miniaturized
systems