Post on 30-Dec-2015
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
Bacterial division Multiplication by binary fission: the
bacteria grows and divides into two identical daughter cells.
Preceded by duplication of the bacterial chromosome with the DNA replication.
Various synthesis and degradation enzymatic systems involved in the cell 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 species20 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 growthFor example, Escherichia coli
G= 20 minutes After 1 hour: 3 cycles : n = 23 = 8 bacteria After 2 hours: 6 cycles : n = 26 = 64 bacteria After 3 hours : 9 cycles : n = 29 = 512 bacteria After 4 hours : 12 cycles: n = 212 = 4096 bacteria After 5 hours : 15 cycles: n = 215 = 32768 bacteria … After 10 hours : 30 cycles : n = 230 = 1073741824 bacteria
More than a billion bacteriaafter 10 hours of culture!
Bacterial growth In liquid culture media :
Clear media
After 16h of culture =
turbid media
Increasing the cell density during the growth
Bacteria
Bacterial growth In solid culture media :
Accumulation of cells during the growth
After 16 - 24h : 1 bacteria 1 visible bacterial
colonyBacteria
Different culture media depending on their useThe isolation and identification media
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
Basal media = all common bacteria culture