Microscopy & Microbiology Lab Fundamentals

Vocabulary flashcards covering essential microscopy concepts, staining techniques, media types, electromagnetic spectrum, and key microbiological terms from the lecture.

Five I’s

The five basic procedures in microbiology—Inoculation, Incubation, Isolation, Inspection, Identification.

Medium (pl. media)

A nutrient-containing preparation used to grow microorganisms in the laboratory.

Selective medium

Culture medium formulated so that only certain microorganisms can grow while others are inhibited.

Differential medium

Culture medium that allows many organisms to grow but distinguishes them by color or appearance.

Mannitol Salt Agar (MSA)

A medium that is both selective (for Staphylococcus spp.) and differential (turns yellow if mannitol is fermented).

Synthetic (defined) medium

Growth medium whose exact chemical composition is completely known.

Complex medium

Medium containing ingredients such as plant, animal, or yeast extracts whose precise chemical composition is unknown.

Nanometer (nm)

Unit of length equal to 10⁻⁹ m; used to measure viruses and wavelengths of light.

Micrometer (µm)

Unit of length equal to 10⁻⁶ m; typical size range for bacteria and eukaryotic cells.

Refraction

The bending of light as it passes between substances of different densities, fundamental to image formation in lenses.

Magnification

Increase in apparent size of an object produced by a lens system.

Ocular lens

The eyepiece of a microscope; usually provides 10× magnification.

Objective lens

Lower lens of a light microscope; common powers are 4×, 10×, 40×, and 100× (oil immersion).

Total magnification

Product of objective power and ocular power (e.g., 40× objective × 10× ocular = 400×).

Oil immersion lens

100× objective lens used with a drop of oil to prevent light scatter and achieve ~1,000× total magnification and 0.2 µm resolution.

Resolution

The ability to distinguish two points as separate; higher resolution means finer detail.

Resolving power

Minimum distance between two objects that allows them to be seen as distinct; ~0.2 µm for the best light microscopes.

Visible light spectrum

Portion of electromagnetic spectrum (≈380–750 nm) perceived by the human eye.

Ultraviolet (UV) radiation

Electromagnetic waves with wavelengths shorter than visible light (< 380 nm); can damage DNA and cause skin cancer.

Gamma rays

High-energy electromagnetic radiation with the shortest wavelengths; highly penetrating and potentially harmful.

Electron microscope

Large instrument that uses electron beams instead of light, providing extremely high magnification and resolution at the cellular or molecular level.

Wet mount

Microscope slide preparation in which a specimen is suspended in liquid (water, saline, broth) for immediate observation of motility and morphology.

Heat fixing

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

Simple stain

Technique using a single basic dye (e.g., methylene blue) to add color and reveal cell shape and arrangement.

Gram stain

Differential staining procedure that classifies bacteria as Gram-positive (purple) or Gram-negative (pink/red) based on cell-wall structure.

Gram-positive bacteria

Bacteria with thick peptidoglycan walls retaining crystal violet–iodine complex; appear purple after Gram staining.

Gram-negative bacteria

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

Acid-fast stain

Differential stain (e.g., Ziehl–Neelsen) that detects waxy-walled Mycobacterium; acid-fast cells appear red, non-acid-fast blue.

Mycobacterium

Genus of acid-fast bacteria with mycolic acid–rich cell walls; includes the tuberculosis pathogen.

Positive (basic) dye

Stain with positively charged chromophore that binds to negatively charged cell components, coloring the cells.

Negative (acidic) dye

Stain with negatively charged chromophore that repels the cell and colors the background instead.

Trichomonas vaginalis

Motile protozoan parasite causing trichomoniasis; visible in wet mounts as a flagellated, squid-like organism.

Whiff test

Diagnostic odor test for bacterial vaginosis or trichomoniasis; adding KOH produces a fishy smell if positive.

Cation

Positively charged ion; basic dyes contain cationic chromophores.

Anion

Negatively charged ion; acidic dyes contain anionic chromophores.

Staphylococcus (Staph)

Gram-positive cocci often isolated on Mannitol Salt Agar; includes S. aureus.

Streptococcus (Strep)

Gram-positive cocci commonly associated with throat infections.

Escherichia coli (E. coli)

Gram-negative rod frequently used as a model organism and indicator of fecal contamination.

Narrow-spectrum antibiotic

Drug effective against a limited range of bacteria, often chosen first to avoid excessive resistance.

Broad-spectrum antibiotic

Drug active against a wide variety of bacteria; reserved for serious or unidentified infections to prevent resistance.

Radio waves

Longest-wavelength electromagnetic waves; low energy, used for communication and harmless to tissues.

Microwaves

Electromagnetic waves shorter than radio waves; cause water molecules to vibrate and heat food.

Infrared radiation

Electromagnetic waves perceived as heat; basis for remote controls and some imaging devices.

Visible-light wavelength and color

Specific colors correspond to specific wavelengths (e.g., blue ≈ 450 nm); objects appear colored by reflecting certain wavelengths.

Oil-immersion resolution limit

Approx. 0.2 µm—the closest distance at which two points can be distinguished using the 100× oil lens.