bacterial culture in laboratory. introduction : bacterial growth
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Bacterial growthBacterial growth
Multiplication by binary fission: the bacteria grows and divides into two identical daughter cells.
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
Bacterial growthBacterial 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!
Culture mediaCulture media Solid Solid by adding a
gelling agent (agar) to a liquid media
LiquidLiquid
Culture in liquid mediaCulture in liquid media
Clear media
After 16h of culture =
turbid media
Increasing the cell density during the growth
Bacteria
Culture in solid mediaCulture in solid media
Accumulation of cells during the growth
After 16 - 24h : 1 bacteria 1 visible bacterial
colonyBacteria
Inoculation techniqueInoculation technique
In liquid media : In solid media (usually with Agar Petri dish) :
Spreading with a rake
Ridges with a loop
Ridges with a swab
Inoculation with pipette
Inoculation with loop
Aseptic conditions in labAseptic conditions in lab
Bacteria to study…
Problem 1 :Bacteria from environment can contaminate the preparation
Problem 2 :Bacteria can contaminate the technician
Problem 3 :Technician can contaminate the preparationNeed a sterile zone around the
preparation !!
Aseptic conditions in labAseptic conditions in labEquipment to create a sterile area to work…
System which uses an HEPA filter (High Efficiency Particulate Air) to generate a flow of sterile air Protection for the preparation and the technician
Microbiological Safety Cabinet :
Aseptic conditions in labAseptic conditions in labEquipment to create a sterile area to work…
Gas burner which delivers a flame at 1300°C
provides a sterile air zone near
Bunsen Burner :
Aseptic conditions in labAseptic conditions in labWorking with a Bunsen Burner :
Convection air movement
Sterile air area :
Approximately 40 cm diameter around the burner
This area is use to open tube or agar Petri dish with bacteria
Aseptic conditions in labAseptic conditions in labOrganization of the workspace
Bunsen Burner is place in the center of the workspace and all instruments are distributed around (aerial view) :
Box with instruments (pipettes,
inoculation loops…)
Trash for contaminated instruments
Rack tubes
Agar Petri dish
Bunsen Burner