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Culturing Bacteria
• Growth Media
• Agars… Solid (derived from
marine algae)
• Petri Dish … isolate colonies
• Slants… to culture (grow)
colonies…aerobes
• Deep tubes… to culture (grow)
colonies…
• Checks for gas requirements
• Anaerobes…deep
• Aerobes surface
• Facultative…mixed
• Checks for motility
Culturing Bacteria
• Broth… LB (Luria Bertani) most
common
• Culture to grow large amounts of colonies
• Amount of growth recorded by turbidity
• Does not offer differential identification
• Differential Growth media…helps
identify specific colonies
• Chromogenic growth media uses
color for identification
• Antibiotic selection uses antibiotic
rich media to select for transformed
bacteria given resistance
• Ampicillin most common
Differential
Growth Media
Kirby-Bauer Disk diffusion test
• Test is used to determine the
sensitivity of different bacteria to
antibiotics
• Zone of inhibition (no growth)
describes either the resistance by
the bacteria to antibiotics or the
sensitivity of the bacteria to the
antibiotics
Streak Plating Bacteria
• Bacterial study requires
isolation of a single colony of
bacteria
• Since most objects contain
many different species of
bacteria a streak plate gives
the observer an opportunity to
choose a single colony for
study
• Serial streak plates are even
more effective
Serial Dilution Method
to Reduce Bacteria
• Often the bacteria are to
numerous to effectively separate
on a single streak plate.
• A serial dilution decreases the
bacteria count 10X with each
dilution
• Each dilution is plated to get an
idea of the amount of bacteria
present by counting the CFUs
(colony forming units)
• #of colonies raised x 10 to the power
of the # of dilutions
• Unit is in CFU/ml
(21CFU x 105) x 1000ml
100ml
1ml