Microbiology Lab Techniques & Microscopy Vocabulary

Vocabulary flashcards covering key microbiology laboratory concepts, media, microscopy, staining techniques, and related terminology mentioned in the lecture.

Culture Medium

A nutrient-rich substance used to grow microorganisms in the laboratory.

Selective Medium

A culture medium formulated so that only specific microbes can grow while others are inhibited.

Differential Medium

A medium that allows many organisms to grow but displays visible differences (e.g., color changes) to distinguish them.

Mannitol Salt Agar (MSA)

A selective-and-differential medium containing high salt and mannitol; promotes growth of Staphylococcus species and differentiates those that ferment mannitol.

Synthetic (Defined) Medium

A growth medium in which every chemical component and its exact concentration are known.

Complex Medium

A medium containing extracts of plants, animals, or yeasts in which the precise chemical composition is unknown.

Refraction

The bending of light as it passes through substances of differing densities, enabling magnification in microscopes.

Magnification

The apparent enlargement of an object produced by a microscope lens system, expressed as a multiple (e.g., 400×).

Ocular Lens

The eyepiece of a microscope that typically provides 10× magnification.

Objective Lens

One of several interchangeable lenses closest to the specimen; common powers are 4×, 10×, 40×, and 100× (oil immersion).

Oil Immersion Lens

The 100× objective lens used with a drop of oil to prevent light scatter and achieve up to 1,000× total magnification.

Resolution

The ability to distinguish two close objects as separate; higher resolution reveals finer detail.

Resolving Power

The minimum distance at which two points can still be seen as distinct; measured in micrometers (µm).

Electron Microscope

A large, high-powered microscope that uses electron beams to achieve extremely high magnification and resolution.

Bright-Field Microscope

A light microscope that illuminates the specimen with white light against a bright background.

Wet Mount

A preparation in which living cells are suspended in a liquid (e.g., saline) on a slide for immediate observation.

Heat Fixation

Passing a smear through flame to kill and adhere microorganisms firmly to the slide before staining.

Stain (Dye)

A colored chemical (basic or acidic) applied to specimens to increase contrast under the microscope.

Simple Stain

A staining technique using a single dye (e.g., methylene blue) to add color to cells without differentiating types.

Differential Stain

A staining method employing multiple dyes to distinguish between groups of microorganisms or cellular components.

Gram Stain

A four-step differential stain that classifies bacteria as gram-positive (purple) or gram-negative (pink/red) based on cell-wall structure.

Gram-Positive Bacteria

Bacteria with thick peptidoglycan cell walls that retain crystal violet and appear purple after Gram staining.

Gram-Negative Bacteria

Bacteria with thin peptidoglycan and an outer membrane; lose crystal violet and take up safranin, appearing pink/red.

Acid-Fast Stain

A differential stain (e.g., Ziehl-Neelsen) used to detect mycobacteria with waxy cell walls that resist Gram staining.

Mycobacterium tuberculosis

Acid-fast bacterium that causes tuberculosis; identifiable by acid-fast staining techniques.

Basic (Cationic) Dye

Positively charged dye (e.g., crystal violet) that binds to negatively charged bacterial components like nucleic acids.

Acidic (Anionic) Dye

Negatively charged dye (e.g., nigrosin) that is repelled by cell surfaces and stains the background.

Positive Stain

Staining approach in which dye colors the cells themselves, leaving the background clear.

Negative Stain

Technique where dye colors the background, providing a dark contrast around unstained cells.

Trichomonas vaginalis

A motile, flagellated protozoan parasite that causes the sexually transmitted infection trichomoniasis; visible in wet mounts.

Bacterial Vaginosis (BV)

Non-STI imbalance of vaginal flora, often producing a fishy odor detectable in a whiff test.

Narrow-Spectrum Antibiotic

An antimicrobial effective against a limited group of bacteria; often used first to reduce collateral damage.

Broad-Spectrum Antibiotic

An antibiotic active against a wide variety of bacteria; reserved for serious or unidentified infections.

Nanometer (nm)

Metric unit equal to one-billionth of a meter; used to measure wavelengths of light and viruses.

Micrometer (µm)

One-millionth of a meter; common unit for measuring bacterial and cellular dimensions.

Ultraviolet (UV) Radiation

High-energy light (below 380 nm) capable of damaging DNA and causing skin cancer.

Visible Light Spectrum

Range of electromagnetic wavelengths (≈380–750 nm) perceptible to the human eye.

Gamma Rays

Extremely short-wavelength, high-energy radiation originating from cosmic sources; highly penetrating and potentially harmful.

Penicillin

A β-lactam antibiotic class commonly effective against many gram-positive bacteria.

Cephalosporin

A broad antibiotic family related to penicillin; often used for gram-negative or resistant infections.