Use of a microscope to observe microorganisms

Preparation before Observation

Start by cleaning the lenses of the microscope with lens tissue to ensure a clear view.
Make sure the microscope is attached to a stable surface and at a suitable height for comfortable usage.
Remember to only use the coarse focus when on the lowest power (usually x4 objective lens), to prevent damage to the lenses.

Preparation of a Slide

Start with a clean glass slide and cover slip.
Apply a small drop of water to the middle of the slide.
Using a pipette or dropper, add a small amount of the microorganism suspension to the water drop. Never touch the pipette directly onto the water drop.
Take a cover slip and hold it at a 45-degree angle with one edge touching the water droplet and let it gently drop on the specimen. This prevents air bubbles being trapped under the cover slip.

Viewing under a Microscope

Place the slide on the microscope stage and hold firmly with stage clips.
Start with the lowest objective lens (usually 4x).
Looking through the eyepiece, use the coarse focus knob to move the stage up just under the objective lens.
Then switch to the high power lens (usually x40) and only use the fine focus knob to bring the object into sharper view to prevent damaging the fine lens.
You should be able to see the microorganisms clearly. Remember, the light intensity may also need adjusting for clear viewing.

Staining Techniques

Staining microorganisms is an important process for better visibility and differentiation. Simple stains like methylene blue can be used to enhance microorganism detail.
Before staining, the specimen needs to be ‘fixed’ onto the glass slide. A heat fix is the common method used.
Procedures for staining techniques vary. For example, in gram staining procedure, crystal violet stain is first applied, followed by a mordant (Gram’s iodine), then decolorisation with alcohol or acetone, and finally counterstained with safranin.
The result of Gram staining helps distinguish between Gram-positive (purple) and Gram-negative (pink) bacteria.
Remember to rinse with water after every step in the staining process to remove excess stain and blot dry before viewing under the microscope.

Remember, always handle microscopes with care and ensure you follow safety guidelines when conducting experiments with microorganisms and stains. Seek teacher assistance if in doubt.