Observing Microorganisms Through a Microscope

Micrometers (µm) are commonly used to measure the size of microorganisms. 1 µm equals 10^-6 meters.

Nanometers (nm) are even smaller than micrometers and are used to measure the size of viruses and other very small structures. 1 nm equals 10^-9 meters.

The compound light microscope uses multiple lenses to magnify the image of a specimen. It allows you to view small structures, like bacteria, that are invisible to the naked eye.

Total magnification is the overall magnification of the image produced by the microscope lenses. It's calculated by multiplying the magnification of the objective lens by the magnification of the eyepiece lens.

Resolution is the ability to distinguish between two closely spaced objects. It's determined by the wavelength of light used and the quality of the lenses.

Darkfield microscopy uses a special condenser to illuminate the specimen from the sides, creating a dark background. This highlights the specimen and makes it appear bright against the dark background.

Phase-contrast microscopy uses a special condenser and objective lens to enhance the contrast between different parts of a specimen. It allows you to see details of transparent structures like bacteria.

Fluorescence microscopy uses a special light source that excites fluorescent molecules in the specimen. These molecules then emit light at a different wavelength, making specific structures appear bright against a dark background.

A type of microscopy that uses sound waves to image specimens, allowing for the observation of living cells attached to surfaces.

A microscope that uses a beam of electrons to create images, offering much higher magnification and resolution than light microscopes.

A type of electron microscope that produces two-dimensional images of thin slices of specimens, revealing internal structures.

A type of electron microscope that creates three-dimensional images of the surfaces of whole specimens, revealing external details.

A technique used to color microorganisms with dyes to make certain structures more visible under a microscope.

A thin film of material prepared for microscopic examination.

A stain that uses a single basic dye to color microorganisms, making their shapes and arrangements visible.

Stains that differentiate bacteria based on their reactions to the stains.

The ability to distinguish two points as separate entities. It is determined by the wavelength of light used and the numerical aperture of the lens.

A type of microscopy that illuminates a specimen with a concentrated beam of light, creating a bright image against a dark background. It is ideal for visualizing unstained, transparent specimens.

A type of microscopy that utilizes a special condenser and objective to enhance the contrast between different parts of a specimen. This method allows for detailed observation of living organisms.

A type of microscopy that utilizes polarizing filters to create a three-dimensional, colored image of the specimen. It allows for the detailed study of living cells.

The use of a fluorochrome dye that absorbs ultraviolet light and emits visible light, illuminating the specimen against a dark background. Enables the detection of specific structures and molecules.

Utilizes a laser to illuminate a specific plane of the specimen. This allows for detailed observation of thick specimens and the creation of 3D images.

A type of microscopy that employs a long-wavelength laser to excite fluorescent molecules, allowing for imaging of thick specimens with minimal photodamage.

A type of microscopy that utilizes sound waves to generate images of biological specimens. It is used for studying specimen density and internal structures.

Acid-fast bacteria resist decolorization with acid-alcohol, indicating a waxy cell wall.

This stain identifies the presence of endospores, which are resistant structures inside some bacteria.

Mycobacteria, like those causing tuberculosis, are acid-fast bacteria. This property made Ehrlich realize they could resist disinfection.

Gram-negative bacteria, such as Neisseria gonorrhoeae, appear red after Gram staining. They are often found in large human cells called phagocytes.

Clue cells are vaginal epithelial cells covered in bacteria, indicating a bacterial infection. The bacteria are often gram-positive.

Acid-fast staining technique differentiates bacteria based on their cell wall composition. Acid-fast bacteria, like Mycobacterium, retain the primary stain (carbolfuchsin) even after treatment with acid-alcohol, appearing red. Non-acid-fast bacteria lose the primary stain and take up the counterstain (methylene blue), appearing blue.

A staining technique that highlights microbial capsules. Capsules are a protective layer surrounding some bacteria. In negative staining, the background is stained, leaving the capsule unstained against a colored background. This makes the capsule clearly visible.

Endospore staining is designed to visualize bacterial endospores, which are highly resistant structures formed by some bacteria. Endospores are stained with a primary stain, usually malachite green, and resist decolorization with water. The rest of the cell is then counterstained with safranin, making them visible as green structures within a red bacterial cell.

Flagella staining aims to visualize bacterial flagella, which are thin appendages used for motility. Due to their thin nature, flagella are difficult to see with a light microscope. Special staining techniques involve thickening the flagella with mordants, using a primary stain, and then a counterstain to make them visible.

The total magnification of a specimen is the product of the magnification of the objective lens and the ocular (eyepiece) lens. For example, if the objective lens magnifies 100x and the ocular lens magnifies 10x, then the total magnification is 1000x.

A mordant is a chemical used in staining to enhance the binding of the primary stain to the specimen. In Gram staining, the mordant (iodine) forms a complex with the primary stain (crystal violet) that traps the stain within gram-positive bacteria. In flagella staining, the mordant helps thicken the flagella, making them easier to visualize.

In Gram staining, a decolorizer (usually alcohol or acetone) is used to remove the primary stain from gram-negative bacteria. This is due to their thinner peptidoglycan layer. Gram-positive bacteria, with their thicker peptidoglycan layer, retain the primary stain.

A counterstain is a secondary stain used in many staining techniques. It stains the cells that have lost the primary stain, allowing them to be visible under the microscope. For example, in acid-fast staining, methylene blue stains the non-acid-fast bacteria blue, while in Gram staining, safranin stains the gram-negative bacteria pink/red.