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 growth After n cycles : 2n bactéria
Bacterial growth For 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 bacteria after 10 hours of culture!
Bacteria Increasing the cell density during the growth After 16h of culture = turbid media Bacterial growth • In liquid culture media : Clear media
After 16 - 24h : 1 bacteria 1 visible bacterial colony Bacteria Accumulation of cells during the growth Bacterial growth • In solid culture media :
Bacterialculture Different culture media
Different cuture media • Solid by adding a gelling agent (agar) to a liquid media • Liquid
Selective media = Contains a selective agent promoting the culture of an exclusive family of microorganism Basal media =all common bacteria culture Identification media = Used to characterize bacteria with differential colorimetric tests Different culture media depending on their use The isolation and identificationmedia
Tubes media Multi-test miniaturized systems Classics tubes Agar plate media Different culture media depending on their use Different packaging of identification media