Transcript Bacterial Cultures

Bacterial Cultures
*Bacteria grow best in warm, moist,
dark areas that contain a lot of food.
-When we culture bacteria, we
provide them with this environment
to grow in via a Petri dish
containing nutrient agar.
Culture – growing a sample of
bacteria in a laboratory.
Petri dish – plastic container in
which bacterial colonies are grown
on nutrient agar.
Nutrient agar – gel-like substance
that provides bacteria with food,
water, and moisture. Is its major
food source.
Sterile vs. Contaminated
-Before a Petri dish is
opened, it is sterile.
-As soon as it is exposed
to the air, it becomes
contaminated.
Sterile – no bacteria are
present.
Contaminated – when
unwanted bacteria enters
the Petri dish.
Inoculating and Incubating
-In order to grow bacteria,
we take a sample from an
object using a sterile Q-tip,
inoculate the Petri dish,
and incubate the sample
over time.
Inoculate – place desired
bacteria into Petri dish
using a sterile Q-tip.
Incubate – place in an area
to keep warm.
Streaking Petri Dishes
Bacterial Growth
-Bacterial growth can be
seen growing on nutrient
agar in the form of
colonies.
Colonies – many bacteria
growing close together.
Growth curve of bacteria culture
j Lag phase:
slow growth
(adjust to environment)
3
k Exponential phase:
rapid growth
l Stationary phase:
reproduction = death rate
m Death phase:
death rate > reproduction
rate
2
1
4
Zones of Inhibition
*Scientists use bacterial
colonies to test the
effectiveness of new
antibiotics and
antimicrobial agents such
as disinfectants and
antiseptics.
Zone of Inhibition – a clear
region around paper discs
that are saturated with an
antimicrobial agent on the
agar’s surface.