Download Gram Staining - Mount Mansfield Union High School

Gram Staining
There are two types of cell walls in
Eubacteria:
–
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
alcohol.
• Finally, the cells are restained
with a pink dye solution called
safranin.
Explanation
•
•
•
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
work:
• Gram positive bacteria tend to be killed by antibiotics
such as penicillin and erythromycin which target the cell
wall.
• 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
Will
Antibiotics
Work?
Illness
Cause
Strep Throat
Streptococcus bacteria
Yes
"Common Cold"
Over 200 different
rhinoviruses
No
AIDS - Acquired
Immune Deficiency
Syndrome
Human Immunodeficiency
Virus (HIV)
No
Epstein Barr Virus or
Cytomegalovirus
No
Common Ear Infection
Usually bacteria
Usually
Chlamydia (STD)
Chlamydia tachomatis
bacteria
Yes
Herpes
Herpes simplex virus
No
"Mono" (Infectious
Mononucleosis)
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
14
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