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simple microscope

microscope has only one lens.


In this microscope the image from the objective lens is magnified again by the ocular lens.
Total magnification = objective lens x ocular lens


the ability of the lenses to distinguish two points.
Limit of Resolution for the light microscope is 0.2 mm.
A microscope with a resolving power of 0.2 mm can distinguish between two points ≥ 0.2 mm.

brightfield illumination

Dark objects are visible against a bright background.
Light reflected off the specimen does not enter the objective lens.

darkfield illumination

Light objects are visible against a dark background.
Light reflected off the specimen enters the objective lens

phase-contrast microscopy

Accentuates diffraction of the light that passes through a specimen.

differential interference contrast microscopy

Accentuates diffraction of the light that passes through a specimen; uses two beams of light.

fluorescence microscopy

Uses UV light. Fluorescent substances absorb UV light and emit visible light. Cells may be stained with fluorescent dyes (fluorochromes).

confocal microscopy

Uses fluorochromes and a laser light. The laser illuminates each plane in a specimen to produce a 3-D image.

electron microscopy

Uses electrons instead of light. The shorter wavelength of electrons gives greater resolution.

Transmission Electron Microscopy (TEM)

Ultrathin sections of specimens. Light passes through specimen, then an electromagnetic lens, to a screen or film.
Specimens may be stained with heavy metal salts. 10,000-100,000x; resolution 2.5 nm

scanning electron microscopy (SEM)

An electron gun produces a beam of electrons that scans the surface of a whole specimen. Secondary electrons emitted from the specimen produce the image.1000-10,000x; resolution 20 nm


A thin film of material containing microorganism on the slide.


Process to preserve microbe and attach it to the slide. (Heat)


addition of a dye to add color to the microorganism.


consist of salts with a positive and negative ion.
Bacteria have slight negative charge at pH=7. Therefore, Basic dyes commonly used to stain bacteria.
Some basic dyes: Crystal Violet, Methylene blue, Malachite Green, Safranin.

basic dye

In a ---, the chromophore is a cation. Bacteria have slight negative charge at pH=7. Therefore, this type of dye is commonly used to stain bacteria. ex: Crystal Violet, Methylene blue, Malachite Green, Safranin.

acidic dye

In an ----, the chromophore is an anion.

Simple Stain

Use of a single basic dye to highlight entire microorganism is called a ----.

Differential Stains

React differently with different species of bacteria, therefore can be used for identification. (ex. Gram stain, Acid-Fast stain)


A ---- may be used to hold the stain or coat the specimen to enlarge it.


bacteria tend to be killed by penicillin and detergents.


bacteria are more resistant to antibiotics.

Acid-Fast stain

binds strongly to bacteria with waxy lipids in cell wall.
Mycobacterium tuberculosis and Mycobacterium leprae are two important pathogens identified.
Primary stain - Carbolfuchsin (Red)
Acid-fast microbes retain red primary stain.
Counterstain - Methylene Blue
Non Acid-Fast cells are blue

Special Stains

are used to color and isolate specific parts of microbes.
1. Capsule - Gelatinous covering of microbe.
2. Endospore - A special dormant structure that survives adverse environmental conditions.
Primary stain - malachite green.
Counterstain - safranin.
Endospores appear green within red/pink cells.
3. Flagella - Structure of locomotion.

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