Medical Technology
Department
Armstrong Atlantic State
University
Savannah, GA
TITLE:
MEDT 3200
Wet Mount
Technique
Effective Date:
08/23
Page 1 of 2
Objectives
At the end of this lab exercise, the student should be able to:
1. Demonstrate how to make and examine a wet mount preparation of living bacteria.
2. Discuss the difference between true motility and Brownian movement.
3. Explain the cause of Brownian movement.
4. Determine the size and shape of various bacteria by wet mount preparation.
5. Name at least one organism that is negative for motility.
6. Name at least one organism that is positive for motility.
7. Demonstrate how to reset Kohler
Introduction
To be proficient in the clinical microbiology laboratory, it is imperative that the
individual be well trained in the wet mount technique. A wet mount is a fast way to
observe bacteria. Direct examination of living microorganisms is very useful in
determining size, shape, and movement. Microorganisms will exhibit either Brownian
movement or true motility. Brownian movement is not true motility. In Brownian
movement, the organisms all vibrate at about the same rate and maintain their relative
positions. Brownian movement is caused by water molecules bouncing around in the
solution, knocking up against each other and the microorganisms. Kinetic energy
inherent to all molecules causes this kind of movement. In contrast, motile organisms
move from one position to another. Most motile bacteria move about with structures
called flagella. Their movement appears more directed than Brownian movement, and
occasionally the cells roll, tumble, or spin.
Materials
Microscope
Lens paper and lens cleaner
Glass slides and cover slips
Disposable pipettes
Proteus vulgaris
Staphylococcus epidermis
Klebsiella pneumoniae
Candida albicans (yeast)
Procedure for wet mount technique
1. Using a disposable pipette transfer a drop of broth to a slide.
2. Holding the cover slip carefully by its edges, place it over the drop.
3. Make sure the microscope is on low power (10x) and place the slide on the
microscope stage. Adjust the condenser on the microscope down to lower the
light and resolution. At this magnification, bacteria are barely discernible as tiny
dots.
4. Examine with high-dry lens (40x), then increase the light and focus carefully.
Bacteria should be magnified sufficiently to see their size, shape and motility.
Some microorganisms are motile, while others exhibit Brownian movement.
5. Record your observations, noting the relative size, shape, and motility of the
organisms.
6. Make a wet mount from the other cultures using the above procedures.
Hints and Precautions
The wet mount technique is a very valuable tool for the microbiologist, because it
is a quick way to observe the size and shape of an organism. Visualization of
microorganisms with the wet mount technique can be difficult due to the size of the
organisms. Because organisms are transparent when suspended in an aqueous solution
you are able to see them easier by lowering the condenser. By lowering the condenser
you lower the resolution and make the bacteria unresolved, which in turn makes them
easier to see, but sacrifices the ability to see fine details. In order to be able to view the
fine details when viewing gram stains Kohler illumination will need to be reset. It is
important to become familiar with the components of the light field microscope and how
those components work together to be able to adjust resolution and the amount of light
depending on the situation.
Observations: Denote the shape of the organism as cocci, rods, or budding yeast.
organism
Proteus vulgaris
Klebsiella pneumoniae
Staphylococcus epidermis
Candida albicans(yeast)
size
shape
motility