Chapter 2 lecture video notes Microbiology Lab and Staining Techniques

Flashcards covering introductory microbiology lab topics, including staining procedures (Gram, acid-fast, endospore, capsule), aseptic techniques, media types, and microscopy concepts.

Wet mount

A microscopic preparation where a culture is placed in a drop of water to observe microorganisms.

Cell morphology

The study of the shape and arrangement of cells as determined microscopically.

Coccus

A spherical-shaped bacterial cell.

Bacillus

A rod-shaped bacterial cell.

Vibrio

A bacterial shape described as a bent rod.

Smear

A nice thin film of microorganisms on a slide made by thinning out an organism in a drop of deionized water.

Heat fix

A procedure using heat to kill microorganisms and attach them to a slide; performed on a slide warmer at $60\,^{\circ}\text{C}$ for $10\,\text{minutes}$.

Basic dye

A cationic stain with a positive charge that has an ionic interaction with the negatively charged cell.

Acidic dye

An anionic stain with a negative charge that is repelled by the negative charge of the cell.

Direct stain

A staining procedure using a basic dye where the cell has color and the background is colorless.

Negative stain

A procedure using an acidic dye, such as India ink, where the background has color and the cell is colorless; notably, no heat fixing is used.

Simple stain

A staining procedure that uses only one basic dye, staining all species on the slide the same color.

Mordant

A substance that does not add color itself but intensifies or enhances a staining procedure, such as iodine in a Gram stain.

Differential stain

A procedure using two different dyes, a primary stain and a counterstain, that must be easily distinguishable from each other.

Gram stain

The most important differential staining procedure, used to divide bacteria into two groups based on cell wall composition.

Crystal violet

The primary stain used in the Gram stain procedure which stains all cells purple.

Decolorizing agent

The differential step in a Gram stain (using acetone alcohol) that removes color from gram-negative cells while gram-positive cells remain purple.

Safranin

The counterstain used in the Gram stain (stains colorless gram-negative cells light red) and the endospore stain (stains vegetative cells red).

Gram variable

A condition in some gram-positive organisms, like the genus Bacillus, where the cell wall becomes leaky with age (over $48\,\text{hours}$) and causes cells to stain inconsistently.

Mycolic acid

A waxy material found in the cell walls of acid-fast cultures like Mycobacterium and Nocardia that makes them difficult to stain.

Acid-fast stain

A differential stain using Carbolfuchsin with moist heat as the primary stain, acid alcohol as the decolorizer, and methylene blue as the counterstain.

Endospore

A metabolically inactive structure that is neither alive nor dead; it can germinate back into a vegetative cell and may release potent exotoxins.

Vegetative cell

An actively growing cell with an active metabolism.

Capsule

An external layer of polysaccharides that acts as a virulence factor, aiding in the ability to cause disease.

Motility

The use of energy ($ATP$) to move through the environment, often facilitated by flagella.

Aseptic techniques

Laboratory techniques used to prevent contamination by unwanted microorganisms.

Agar

An inert, complex polysaccharide added to media as a solidifying agent; it cannot be used as a source of energy or nutrients.

Colony morphology

The macroscopic appearance of a microorganism growth on solid media, including color and shape.

Deep

A type of solid media in a tube used specifically to determine motility and oxygen demands.

Sterile

An all-or-nothing state where absolutely no forms of life (cells, endospores, or viruses) are present.

Autoclave

Equipment used for sterilization, typically set to $15\,\text{psi}$ of pressure at $121\,^{\circ}\text{C}$ for $15\,\text{minutes}$.

Turbidity

Cloudiness in a liquid broth, which is an absolute sign of growth.

Flame sterilization

The process of heating an inoculating loop or needle until it glows orange to red, reaching approximately $1,800\,^{\circ}\text{C}$.

Compound microscope

A microscope that uses two lenses (ocular and objective) to magnify an image.

Total magnification

The product of the magnification of the objective lens and the ocular lens ($\text{Objective} \times \text{Ocular}$).

Resolution

The ability of a microscope to see fine detail and keep an object in focus as it is enlarged.

Immersion oil

Oil used with the $100\times$ objective that has the same refractive index as glass to prevent light from bending and improve resolution.

Bright field microscope

A commonly used microscope where the background is bright and the specimens are usually stained.

Transmission electron microscope

A tool used to capture highly detailed internal images of a cell.

Scanning electron microscope

A tool used to capture highly detailed external images of the cell surface.