Before you play an 18-hole game of golf you need to learn how to swing. This
lab is intended to increase your microscopy skills. Many of the bacteria
will be looking at are taken from clinical samples. Their morphology is often
the first step in their diagnostic identification. The prepared slides
are viewing have all been stained. You will be doing several of these same
stains in lab in the next few weeks. Look (and record) how the cells are
on the slide, at the intensity of the stains, at the size and shape of the
cells, for special features and how the cells are arranged together. Please
remember that bacteria rarely exist by themselves as you see them on these
slides. They live in consortiums with other species of bacteria and can
complex structural communities. You have 20 slides to view in this exercise.
You can choose to individually focus all 20 slides or each group of
4 can focus
5 slides each and observe one anotherís specimens. Teamwork - divide and
conquer! You can click on most of the names and get an image from the slides
here in the lab. Hit the back button on the menu bar to return to this page.
- Bacteria, Yeast, and Blood - This mixed smear shows typical
bacilli, yeast, and human blood cells. Pay particular attention
to their respective sizes. Even the biggest bacteria are smaller
than yeast, which are still smaller than a typical human red
- Bacterial Types - This smear is a mix of typical bacilli, cocci,
aureus - This smear shows typical gram positive cocci.
Staph. aureus is frequently found in the human respiratory
tract and on the skin.
- Micrococcus luteus
- These gram positive cocci, typically arranged in tetrads, are
normal flora of mammalian skin.
- Neisseria gonorrhoeae
- These gram negative diplococci are the causative agent of gonorrhea.
This is a smear of pus from a lesion. Look for kidney shaped pairs
of cocci. The cells are flattened where they are adjacent.
- Streptococcus faecalis - Shows typical chains of cocci.
- Bacillus - This mixed smear shows typical gram positive and gram negative
- Bacillus anthracis - These
long chains of rod-shaped cells have centrally located endospores. Endospores
are a resting structure formed inside the cell that allows the bacteria to
survive harsh conditions for extended periods. Look for red spores inside
These spore-forming streptobacilli are the causative agent of anthrax.
- Clostridium tetani - Observe
the characteristic drumstick shape of these cells. The endospores are round
and terminal. These anaerobes are the causative agent of tetanus.
- Mixed Coliforms - Mixed smear showing various species of bacteria found
in the human intestine; indicates fecal contamination in water supplies.
Mycobacterium tuberculosis -
These gram-resistant, slightly curved bacilli are the causative agents
of tuberculosis. Due to
a special wax
cell membrane, these organisms do not readily take up dye from a typical
gram stain. Instead, an acid-fast stain using either heat or detergant
is performed in order to break through this protective waxy layer.
- Pseudomonas aeruginosa - These gram negative, slightly curved bacilli cause
infections in wounds, burns, and urinary tracts.
Spirochetes, Helicals, Spirillium, Vibrio
- The causative agent of Lymeís disease. It is about 0.3 micrometers in
diameter and 15 micrometers in length. Its helical structure stands out
against the RBCís.
Treponema pallidum - The causative of syphilis. It is a spirochete that is best viewed live with dark-field microscopy.
- Typical Spirillium - Smear showing typical spirillium bacteria.
- Vibrio cholerae - These comma-shaped gram negative rods are the causative
agent of Cholera.
Flagella, Capsules, Archae
Capsules - Notice the background of the slide is colored so
that you can see the protective slime coating secreted by many
Flagella (Peritrichous) - Many bacteria are motile because
they possess whip-like flagella. Peritrichous flagella are distributed
all over the cell; monotrichous flagella indicate just one; tufts
of flagella at both ends of the cell are amphitrichous; and tufts
of flagella at one end of the cell are lophotrichous. This is
a very difficult and time-consuming stain because the flagella
are very thin and fragile.
Flagella (Polar Amphitrichous) - Many bacteria are motile
because they possess whip-like flagella. Peritrichous flagella
are distributed all over the cell; monotrichous flagella indicate
just one; tufts of flagella at both ends of the cell are amphitrichous;
and tufts of flagella at one end of the cell are lophotrichous.
This is a very difficult and time-consuming stain because the
flagella are very thin and fragile.
- This is a collection of ancient bacteria. Look for rods, cocci
and involuted, often square shaped cells. The species represented
here are extreme halophiles (salt-lovers) and methangens (able
to live off of methane).