Microbial Dimensions and Microscopy Techniques

These vocabulary flashcards cover microbial dimensions, the principles of light microscopy, and various staining techniques used to identify and characterize microorganisms.

Refraction

The bending or change in the angle of a light ray as it passes through a medium such as a lens.

Ocular lens

The lens closest to the eye, also known as the eyepiece, which forms the virtual image.

Objective lens

The lens closest to the specimen which forms the real image.

Magnifying power

The total magnification of a microscope calculated by multiplying the power of the ocular lens by the power of the objective lens.

Resolution

The capacity of an optical system to distinguish or separate two adjacent objects or points from one another.

Resolving power

The minimum distance two objects can be apart and still be distinguished separately, determined by lens characteristics and the wavelength of light.

Oil Immersion Lens

A $100\times$ objective lens that uses oil to prevent light scattering and increase numerical aperture, allowing resolution of objects $0.2\,\mu\text{m}$ apart.

Refractive index

The degree of bending light undergoes as it passes from one medium to another; a higher index results in greater contrast.

Fluorescence microscope

A light microscope variation that uses ultraviolet radiation as the illuminating source.

Confocal microscope

A light microscope variation that uses a laser beam as the illuminating source.

Wet Mount

A specimen preparation consisting of a drop of culture on a slide overlaid with a coverslip, used for quick assessment of size, shape, and motility.

Heat fixing

The process of gently heating an air-dried smear to kill cells, secure the specimen to the slide, and preserve cellular components with minimal distortion.

Basic (cationic) dyes

Dyes that have a positive charge and are attracted to the negatively charged components of bacterial cell walls.

Acidic (anionic) dyes

Dyes that have a negative charge and are repelled by the acidic, negatively charged components of bacterial cell walls.

Positive stain

A technique where a positively charged stain is attracted to negatively charged cell walls, causing the dye to stick to the cell and impart color.

Negative stain

A technique where a negatively charged dye is repelled by bacterial cell walls, resulting in a black background around the cells.

Gram stain

A universal diagnostic staining technique that differentiates bacteria into Gram-positive (purple) and Gram-negative (pink) based on cell wall color reactions.

Acid-fast stain

A differential stain that identifies agents of tuberculosis and leprosy; acid-fast bacteria stain pink, while nonacid-fast bacteria stain blue.

Endospore stain

A diagnostic stain used to distinguish endospores from vegetative cells, detecting members of the genera Bacillus and Clostridium.

Capsule

An unstructured protective layer surrounding some bacteria and fungi, often visualized using negative staining with India ink.

Flagella

Tiny, slender filaments used by bacteria for movement, which must be coated and enlarged during the staining process to be visible.