Microbiology Media, Culturing, and Microscopy Vocabulary

Flashcards covering key terms and concepts on microbial growth media, isolation techniques, microscopy principles, and differential staining procedures.

Agar

A complex polysaccharide solidifying agent isolated from the red alga Gelidium; it liquefies at $100^\circ\text{C}$ and solidifies at $42^\circ\text{C}$.

Defined media

Media whose chemical compositions are precisely chemically defined and contain pure organic or inorganic compounds that do not vary from one source to another.

Complex media

Media containing at least one component that is not chemically definable, such as extracts of animals, plants, or yeasts.

Fastidious bacteria

Bacteria that require specific growth factors (such as vitamins or amino acids) and complex organic nutrients to grow.

Selective media

Media containing one or more agents that encourage a select microbe to grow while inhibiting others.

Differential media

Media that allow multiple types of microbes to grow while displaying visible differences between colonies, such as variations in color, size, media changes, or gas bubbles.

The Five I's

The five basic techniques used by microbiologists to manipulate, grow, examine, and characterize microorganisms: Inoculation, Incubation, Isolation, Inspection, and Identification.

Pure culture

A container of medium that contains only a single known species or type of microorganism.

Contaminated culture

A culture that was once pure or mixed but now contains unwanted microbes of uncertain identity.

Colony

A discrete mound of microbial cells on a solid medium, typically formed from a single parent cell.

Streak plate method

An isolation procedure where a small droplet of culture or sample is spread across the surface of a solid medium using an inoculating loop to perform serial dilution.

Pour plate method

An isolation technique (also called loop dilution) in which a sample is mixed with warm liquid agar ($45\text{--}50^\circ\text{C}$) and poured into a sterile Petri dish to solidify.

Spread plate technique

An isolation technique in which a liquid sample is poured onto solid medium and spread evenly across the surface using a sterile spreading tool or hockey stick.

Resolution

The capacity of an optical system to distinguish or separate two adjacent objects or points from one another; also known as resolving power.

Numerical aperture

A measurement representing the relative efficiency of a lens to bend light rays.

Positive stain

A technique using basic dyes that are attracted to negatively charged bacterial cell walls, staining the cell itself.

Negative stain

A technique using acidic dyes (such as India ink or nigrosin) that are repelled by negatively charged cell walls, leaving the cells clear and staining the background.

Gram stain

A differential staining method using crystal violet, Gram's iodine, ethanol decolorizer, and safranin to distinguish Gram-positive (purple) from Gram-negative (pink) cells.

Acid-fast stain

A differential stain used to distinguish acid-fast bacteria (such as M. tuberculosis, which resist acid-alcohol decolorization and stain red) from non-acid-fast cells (which stain blue).

Endospore stain

A differential procedure (Schaeffer-Fulton method) using heat and malachite green to stain endospores bluish-green, counterstained with safranin to color other structures pink to red.