Chapter 3: Microscopes

Micrometer (µm)

1 x 10^-6 meters, or 0.000001 meters

Nanometer (nm)

1 x 10^-9 meters, or 0.000000001 meters

Light microscopy

The use of any kind of microscope that uses visible light to observe specimens

Compound light microscope

An instrument with two sets of lenses that uses visible light as the source of illumination

Illuminator

The light source of a microscope

Condenser

Lens system located below the microscope stage that directs light rays through the specimen

Objective lenses

The lenses closest to the specimen

Ocular lens

The lens closest to the viewer (eyepiece)

Total magnification

The magnification of a microscopic specimen, determined by multiplying the ocular lens magnification by the objective lens magnification

Resolution

The ability to distinguish fine detail with a magnifying instrument; also called resolving power

Refractive index

The relative velocity with which light passes through a substance

Brightfield illumination

A microscope that sues visible light for illumination; the specimens are viewed against a white background

Darkfield microscope

A microscope that has a device to scatter light from the illuminator so that the specimen appears white against a black background

Phase-contrast microscope

A compound light microscope that allows examination of structures inside cells through the use of a special condenser.

Differential interference contrast (DIC) microscope

An instrument that provides a three-dimensional, magnified image

Fluorescence microscope

Microscope that uses an ultraviolet light source to illuminate specimens that will fluoresce

Fluorescence

The ability of a substance to give off light of one color when exposed to light of another color

Fluorescent-antibody (FA) technique

A diagnostic tool using antibodies labeled with fluorochromes and viewed through a fluorescence microscope; AKA immunofluorescence

Antigen

Any substance that causes antibody formation; also called immunogen

Confocal microscopy

a light microscope that uses fluorescent stains and laser to make two and three dimensional images

Two-photon microscope (TPM)

A light microscope that sues fluorescent stains and long wavelength light

Scanning acoustic microscope (SAM)

a microscope that uses high frequency ultrasound waves to penetrate surfaces

Electron microscope

A microscope that sues electrons instead of light to produce an image

Transmission electron microscope (TEM)

An electron microscope that provides high magnifications (10,000-100,000x) of thin sections of a specimen

Scanning electron microscope (SEM)

An electron microscope that provides three dimensional views of the specimen magnified 1,000-10,000x

Scanned probe microscope

Use various kinds of probes to examine the surface of a specimen at very close range, and they do so without modifying the specimen or exposing it to damaging, high-energy radiation

Scanning tunneling microscopy (STM)

Uses a thin metal probe that scans a specimen and produces an image revealing the bumps and depressions of the atoms on the surface of the specimen

Atomic force microscopy (AFM)

a metal and diamond probe is gently forced down onto a specimen. As the probe moves along the surface, its movements are recorded, and a 3-d image is produced

Staining

coloring the microorganisms with a dye that emphasizes certain structures

Fixed

attached to the microscope slide

Smear

thin film of material containing the microorganisms

Basic dye

The color is in the positive ion for the dye

Acidic dye

The color is in the negative ion of the dye

Negative staining

Preparing colorless bacteria against a colored background

Simple stain

an aqueous or alcohol solution of a single basic dye

Mordant

Chemical additive that is added to the solution to intensify the stain

Differential stain

a stain that distinguishes objects on the basis of reactions to the staining procedure

Gram stain

A differential stain that classifies bacteria into two groups, gram-positive and gram-negative

Primary stain

Basic purple dye, usually crystal violet. It imparts its color to all cells

Decolorizing agent

removes the purple from the cells of some species but not of others (used after iodine, which is the mordant, is put on the slide)

Gram-positive

Bacteria that retain the purple color after the alcohol has attempted to decolorize them

Gram-negative

Bacteria that lose the purple color after the alcohol has attempted to decolorize them (no longer visible then, so a counterstain is added)

Counterstain

Stains such as safranin that have a contrasting color to the primary stain

Acid-fast stain

Stain that binds strongly only to bacteria that have a waxy material in their cell walls

Special stains

Used to color and isolate specific parts of microorganisms, such as endospores and flagella, and to reveal the presence of capsules

Capsule

Gelatinous covering over many microorganisms

Virulence

The degree to which a pathogen can cause disease

Endospore

Special resistant, dormant structure formed within a cell that protects a bacterium from adverse environmental conditions

Flagella

Structures of locomotion too small to be seen witha light microscope without staining