Gram Staining - Mount Mansfield Union High School

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Gram Staining - Mount Mansfield Union High School
Gram Staining
There are two types of cell walls in
Gram-positive bacteria have a thick peptide
layer, retain the crystal violet, and appear
purple when viewed under a microscope.
• Gram-negative bacteria have a thin
peptide layer and space surrounding it so
the cell wall is more protected. They take
up the pink stain, and appear pink when
viewed under a microscope.
Gram Staining Technique
• Cells on a microscope slide
are stained with a purple dye
solution called crystal violet.
• The cells are then washed
with water.
• An iodine stain solution is
applied to the cells.
• The slide is then washed with
• Finally, the cells are restained
with a pink dye solution called
Photograph A: E. coli a common gram-negative rod found in the colon –
single cell
Photograph B: Staphylococcus epidermidis a gram-positive cocci found on
the skin – clusters or chains
Photograph C: Bacillus cereus a gram-positive rod found in the soil- chains
Killing Eubacteria
– There are many
chemicals that are lethal
to bacteria:
• cyanide does a good
job — but it’s lethal to
the host as well.
– The way antibiotics
• Gram positive bacteria tend to be killed by antibiotics
such as penicillin and erythromycin which target the cell
• Gram negative bacteria are resistant to these drugs
because their cell wall is protected, but are sensitive to
streptomycin and tetracycline.
• Broad spectrum antibiotics target either the bacteria’s
ability to make proteins or replicate their DNA.
Evolution of Antibiotic Resistance:
• 40-50 years ago, thanks to antibiotics, scientists thought
medicine had all but eradicated infectious agents as a
major health threat.
• More recently, an upsurge of infectious disease is a
problem we have unwittingly created for ourselves b/c:
– rapid, frequent, and relatively cheap international travel allows
diseases to leap from continent to continent
– Many people have inadequate sanitation and lack of clean
drinking water
– We have overused the "miracle drugs“ to treat such diseases to
the point that they lose their potency
• Whenever antibiotics are used, a few of the “enemy” are
able to survive the drug.
• Mutations-
– Because microbes reproduce so quickly and often some random mutation
eventually will protect against the drug.
• When antibiotics are used only when needed and as directed
they usually overwhelm the bugs.
• By using antibiotics too often, more resistant mutants arise.
• When patients cut short the full course of drugs, the resistant
strains have a chance to multiply and spread.
Controlling Microbial Growth
Strep Throat
Streptococcus bacteria
"Common Cold"
Over 200 different
AIDS - Acquired
Immune Deficiency
Human Immunodeficiency
Virus (HIV)
Epstein Barr Virus or
Common Ear Infection
Usually bacteria
Chlamydia (STD)
Chlamydia tachomatis
Herpes simplex virus
"Mono" (Infectious
How Bacteria Cause Disease
• Metabolizing the host– Heterotrophic bacteria obtain nutrients by
secreting enzymes that break down organic
structures and absorb them
– If the environment is your throat or lungs, this
can cause serious problems!
• Ex.
– Tuberculosis settles into the lungs and use human tissue
as their nutrients
– Propionibacterium acnes causes acne
• ToxinsSome bacteria secrete chemical
compounds into their environment
which are poisonous to eukaryotic
cells (toxic)
– Ex. Diptheria grows in the throat,
but the toxins attack the heart,
nerve, liver and kidneys
– Food poisoning occurs when
humans eat food where bacteria
have grown and produced toxins
– One milligram of pure Botulinum toxin is enough
to kill 1 million guinea pig
Controlling Bacteria
3 ways to control bacteria:
1) Heat
Canning the process of sealing food in airtight cans or jars after killing bacteria
•endospores are killed during this process
Pasteurization- process of heating milk to kill
harmful bacteria
2) Dehydration- removing water from food
•Bacteria can’t grow when H2O is removed
•example: uncooked noodles & cold cereal
3) Freeze- inhibits bacteria
Bacteria can also be Helpful!
• Decomposers help recycle nutrients into
the soil for other organisms to grow
• Bacteria grow in the stomach of a cow to
break down grass and hay
Helpful Bacteria
•Used to treat sewage
Organic waste is consumed by the
bacteria, used as nutrients by the
bacteria, and is no longer present to
produce odors, sludge, pollution, or
unsightly mess.
•foods like yogurt, cottage & Swiss cheese, sour cream, buttermilk
are made from bacteria that grows in milk
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