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Bacteria
Bacteria in the Lab:
Growing Bacteria for Studies
• Culture - A bacterial growth (colonies of
cells) maintained in the laboratory.
Growth Media:
• Nutrient Broth- a liquid growth medium
used in flasks, culture bottles or test tubes.
Agar- a solid-type of culture medium
made from seaweed that has a
somewhat rubbery or gel-like
consistency. It is used in a “culture
dish”
Bacteria reproduce by splitting in
half-----called Binary Fission.
If this growth pattern continued for several days, bacteria would cover the
planet!
This is known as exponential growth.
Exponential growth occurs when individuals of a
population reproduce at a constant rate.
J- growth
curve
The bacterial culture eventually reaches carrying
capacity however and the unchecked growth
stops.
Carrying capacity - is the largest numbers of
individuals that a given environment can
support.
S-growth
curve
as resources
become less
available,
population
growth slows
or stops)
Carrying capacity is related to Environmental Resistance
factors: environmental factors such as limited space,
limited food, and an abundance of cellular waste
products that inhibit the bacterial cell population’s
growth, and finally, put an end to the bacterial culture.
Identification of Bacteria based on
OXYGEN REQUIREMENTS:
Obligate Aerobe – must live in the presence of O2
(metabolism - cell respiration) Example:
Mycobacterium tuberculosis
Obligate Anaerobe – can’t live in the presence of
O2 (metabolism - fermentation) Examples:
Clostridium tetani – causes tetanus
Clostridium botulinum – causes Botulism
Facultative Anaerobe – can live under both
conditions (with or without O2) (metabolism – cell
respiration or fermentation) Example: Escherichia
coli in human intestines
Test tube
cultures
based on
O2
Identification of bacteria based on
shapes and arrangement:
1) single spheres
2) two spheres
3) bunches of spheres
4) four spheres
5) Eight spheres – 4
behind 4
6) chain of spheres
7) rod-shaped
8) two rods
9) chain of rods
10) spiral
(spirilla)
11) comma
Identification by Gram Staining
Developed by Dutch Physician Dr. Hans
Christian Gram. He wanted to
differentiate bacteria from patient cell
nuclei in tissue slides.
Most Species of Eubacteria can be
grouped into two categories based on
their response to laboratory stain:
GRAM + or GRAM -
GRAM +:
The bacteria that retain crystal violet stain
& appear purple. They have a thick cell
wall layer known as peptidoglycan that
holds the stain. Peptidoglycan is
composed of protein and carbohydrate.
These cells produce exotoxins.
GRAM The bacteria that have a thinner peptidoglycan
layer and therefore do not retain the gram stain.
They are counterstained with a pink stain called
safranin.
An outer layer of lipids and carbohydrates hold
the pink color. These cells produce endotoxin.
E.coli
The peptidoglycan layer – a protein &
carbohydrate layer within the cell wall.
It is affected by antibiotics. It is not present in
archaebacteria and is a determining factor in the
Gram staining procedure.
• The Center for Disease control estimate that 100,000 in
the US die of septic shock each year, making it the 13th
leading cause of death. Roughly half of all sepsis
patients die, even if an antibiotic manages to clear the
bacteria from the bloodstream.
• Gram negative bacterial walls are thinner and made
of a lipopolysaccharide endotoxin, which brings
about the rapid deterioration characteristic of the
sepsis syndrome.
• As long as the cell wall is intact, the endotoxin presents
little health hazard. But, when the immune system or
antibiotics attack gram-negative bacteria, they expose a
“toxic region” at the root of the endotoxin molecule,
which leads to the high fever and blood pressure drop
that can be fatal.
Identification by Colonial shape: Observations
of a bacterial colony’s shape and characteristics
within a culture dish.
Structures & Functions
• cell wall - protects the bacteria, supports
the cell, prevents bursting
• outer membrane – protects the cell from
some antibiotics(only present in gram –
cells)
• cell membrane
regulates movement of materials in & out of the
cell. It also contains enzymes important to cell
respiration
• cytoplasm – contains DNA, ribosomes, and
organic compounds
• chromosome (bacterial DNA) It is
arranged in a single closed loop. It carries
genetic information inherited from past
generations. (also referred to as a nucleoid)
plasmid – a circular, self-repeating loop of DNA.
It contains some genes obtained through genetic
recombination.
• capsule & slime layer – protects the cell
and assists in attaching the cell to
surfaces (glycocalyx – a fuzzy coat of
sticky sugars in the capsule layer enables
bacteria to stick to the surface of host
cells and tissues.)
• endospore – Some gram + cells can form a thick-
coated resistant structure cell when environmental
conditions are harsh. The harsh conditions may
destroy the original cell, but the endospore and the
cell’s DNA survive. When good conditions return,
the endospore gives rise to a normal bacterial cell.
(pg469)
The endospore is the reason that boiling
water does not always kill all bacteria. An
autoclave is used to sterilize surgical &
dental tools which is a device that uses
high temperature steam under pressure.
• pilus (pili = plural) – assists the cell in attaching
to other surfaces, which is important to
recombination (serves as a conjugation bridge to
transfer plasmids from one cell to another).
• flagellum – moves the cell – long whip-like
extensions. They are made of protein and turn
like a propeller. There can be one, a tuft, at one
end, at both ends, or completely surrounding the
cell.
Bacterial Movement
• 1) Flagella movement: They turn to propel the
bacteria in an erratic, “run and tumble” motion.
• 2) Some bacterial produce a layer of slime and
glide in the slime by wavelike contractions.
• 3) Some spiral shapedbacteria move with a
corkscrew- like rotation.
• 4) Other bacteria have flexible cell walls and cell
wall filaments that contact to cause the bacteria to
turn and move ahead.