Bacteria are microscopic
organisms whose single cells have neither a membrane-bounded nucleus nor other
membrane-bounded organelles like mitochondria and chloroplasts.
The Gram stain is named after the
19th century Danish bacteriologist who developed it.
- prokaryotic (no
- no mitochondria or
- a single chromosome
- a closed circle of
- with no associated
- If flagella are present,
they are made of a single filament of the protein flagellin; there are none
of the "9+2" tubulin-containing microtubules of the eukaryotes.
- ribosomes differ in their
structure from those of eukaryotes
- have a rigid cell wall made
- The plasma membrane (in
Gram-positive bacteria) and both membranes in Gram-negative bacteria are
phospholipid bilayers but contain no cholesterol or other steroids.
- no mitosis
- mostly asexual reproduction
- any sexual reproduction
very different from that of eukaryotes; no meiosis
- Many bacteria form a single
spore when their food supply runs low. Most of the water is removed from the
spore and metabolism ceases. Spores are so resistant to adverse conditions
of dryness and temperature that they may remain viable even after 50 years
- bacilli: rod-shaped
- cocci: spherical
- spirilla: curved walls
- ability to form spores
- method of energy production
(glycolysis for anaerobes, cellular respiration for aerobes)
- nutritional requirements
- reaction to the Gram stain.
Although the Gram stain might
seem an arbitrary criterion to use in bacterial taxonomy, it does, in fact,
distinguish between two fundamentally different kinds of bacterial cell walls
and reflects a natural division among the bacteria.
- The bacterial cells are
first stained with a purple dye called crystal violet.
- Then the preparation is
treated with alcohol or acetone.
- This washes the stain out
of Gram-negative cells.
- To see them now requires
the use of a counterstain of a different color (e.g., the pink of safranin).
- Bacteria that are not
decolorized by the alcohol/acetone wash are Gram-positive.
Gram stain Introduction
Sized tutorials, the gram stain
Differentiation by Gram's Stain
Medical Encyclopedia: Endocervical Gram stain
HISTOLOGICAL SPECIMEN STAINING
Famous scientist quote:
"The sciences gain by mutual support. When, as the result of my first
communications on the fermentations in 1857-1858, it appeared that the ferments,
properly so-called, are living beings, that the germs of microscopic organisms
abound in the surface of all objects, in th air and in water; that the theory of
spontaneous generation is chimerical; ..." Louis Pasteur (1822 -
1895) developed a method of inoculation of cattle for anthrax proving the
efficacy of vaccinations.