BI252-L Microbiology Laboratory Study Guide (Labs 1-6)

Vocabulary practice flashcards covering laboratory safety, microscopy, aseptic technique, culturing, differential staining, enumeration, and microbial environmental growth requirements from Labs 1 through 6.

Aseptic technique

A set of practices used to prevent unwanted microorganisms from contaminating cultures and to prevent cultured microorganisms from contaminating the environment.

Biohazard

Material that may contain biological agents capable of causing harm and therefore must be handled and discarded appropriately.

Sterile

Free of viable microorganisms for the purpose of the laboratory procedure.

Contamination

The unwanted introduction of microorganisms or other unwanted material into a sample, culture, surface, or instrument.

Autoclave

A sterilization system used for treating contaminated laboratory materials before disposal.

Disinfection

Reduction or removal of microorganisms from a surface using a disinfectant, such as $3\%$ hydrogen peroxide or $70\%$ ethanol.

Cross-contamination

The transfer of microorganisms from one culture or material to another unintended culture or material.

Convection current

Movement of air produced by heating; flaming the mouth of a vessel produces an outward current that reduces the entry of microorganisms.

Aerosol

Tiny airborne particles or droplets that can be released when rapid heating causes a microbial culture to splatter.

Microbiology Laboratory Tools

Standard bench equipment including incinerators, inoculating loops/needles, tube racks, biohazard bins, vortex mixers, spreaders, Bunsen burners, strikers, Kimwipes, bibulous paper, and lens paper.

Magnification

How much a lens increases the apparent size of an object.

Resolution

The ability to distinguish fine detail between two close structures in a magnified image.

Parfocal

A microscope property where objectives allow a specimen focused under one objective to remain nearly focused when switching to another objective.

Immersion oil

An optical oil with a refractive index of $1.515$ (matching glass) used with the $100\times$ objective to reduce light refraction and light loss.

Total Magnification Formula

$$\text{Total Magnification} = \text{Ocular Magnification} \times \text{Objective Magnification}$$

Bright-field microscopy

A microscopy approach where light passes directly through the specimen; staining is commonly required to increase the contrast of transparent cells.

Dark-field microscopy

A microscopy approach where only light scattered or reflected from the specimen enters the objective, showing a bright specimen on a dark background.

Phase-contrast microscopy

A microscopy technique that uses optical components to enhance refractive-index differences, ideal for viewing living, unstained cultures with minimal damage.

Transmission Electron Microscopy (TEM)

An electron microscopy method where electrons pass through a thin slice of a specimen, producing detailed two-dimensional internal cellular images.

Scanning Electron Microscopy (SEM)

An electron microscopy method that evaluates electron reflection from a specimen's surface to create a three-dimensional view of surface structures.

Smear

A thin film of microbial cells spread across a microscope slide.

Heat fixation

The process of gently heating a dried smear to kill cells and firmly attach them to the glass slide.

Chromophore

The chemical functional group within a dye molecule that imparts color.

Auxochrome

A chemical group in a dye that enables the chromophore to ionize and bind to cellular material.

Basic dye

A cationic (positively charged) dye attracted to negatively charged bacterial cell surfaces at normal pH.

Acidic dye

An anionic (negatively charged) dye repelled by negatively charged cell surfaces, used primarily to stain the background.

Simple stain

A staining procedure using a single dye primarily to enhance contrast and reveal cell size, shape, and arrangement.

Differential stain

A staining technique using multiple reagents to distinguish between different groups of microorganisms based on structural or chemical differences.

Pure culture

A laboratory culture containing only a single species or type of organism.

Mixed culture

A microbial population containing more than one type of microorganism.

Colony

A clone composed of progeny from a single organism or cell group that multiplied in a fixed position on solid media.

Streak plate

An isolation technique that spreads cells across an agar surface so individual cells give rise to separated colonies.

Colony Morphology Parameters

The phenotypic characteristics used to describe a colony, categorized by elevation (convex, umbonate, flat), margin (smooth, rhizoid, lobate), and whole colony form.

General purpose media

Culture media (e.g., GNA, TSA) containing basic nutrients that support diverse non-fastidious microbial populations without specific inhibitors.

Enrichment media

Culture media containing additives (such as blood, serum, or egg proteins) to promote the growth of fastidious organisms without actively inhibiting others.

Selective media

Culture media containing chemical agents that inhibit specific unwanted microorganisms so desired organisms can grow.

Differential media

Culture media containing indicators that yield distinct colony or agar appearances based on bacterial metabolic activity.

Turbidity

The cloudiness of a broth culture caused by suspended microbial cells.

Slant Growth Patterns

Surface growth patterns along inoculated agar slants, categorized as filiform, arborescent, beaded, effuse, rhizoid, or echinulate.

Gram-positive bacteria

Bacteria with a thick, peptidoglycan-rich cell wall and single membrane that retain crystal violet and appear purple.

Gram-negative bacteria

Bacteria with a thin peptidoglycan layer between two membranes containing lipopolysaccharide (LPS), losing crystal violet during decolorization and taking up safranin to appear pink/red.

Peptidoglycan

A polymer of sugars and amino acids that forms the primary structural wall in bacteria.

Lipopolysaccharide (LPS)

A membrane component of Gram-negative bacterial outer membranes that can elicit strong host immune reactions.

Gram Stain Sequence

A four-step differential staining procedure consisting of primary stain (crystal violet), mordant (Gram's iodine), decolorizer (alcohol), and counterstain (safranin).

Enumeration

Determining the total number or concentration of viable microorganisms in a liquid sample.

Serial dilution

A sequence of controlled dilutions used to step-down microbial concentration so individual colonies can be counted.

Colony-forming unit (CFU)

The unit representing a colony formed on solid media, serving as an estimate of viable starting cells.

CFU Calculation Formula

$\text{CFU/mL} = \text{colony count} \times \text{final dilution factor}$ (applied to statistically significant plates with $30$ to $300$ colonies).

Optical density (OD)

An indirect measure of cell concentration based on how a liquid culture scatters/absorbs light at a given wavelength (e.g., $600\,nm$).

Spectrophotometer

An instrument used to measure light absorbance or transmittance through liquid samples at specific wavelengths.

Blank

An uninoculated medium sample used to zero a spectrophotometer and subtract background light absorbance.

Endospore

A highly resistant, dormant structure formed by certain bacteria to survive extreme environmental conditions like heat, drying, and low nutrients.

Vegetative cell

An actively growing and metabolizing bacterial cell, as opposed to a dormant endospore.

Acid-fast organism

A cell that retains primary stain despite acid-alcohol decolorization due to a thick, waxy mycolic acid cell wall.

Mycolic acid

A waxy lipid component in the outer envelope of Mycobacteria that prevents ordinary Gram stain penetration.

Microbial Temperature Growth Ranges

Thermal growth classifications based on optimal temperature preferences: psychrophiles ($0-20\,^\circ\text{C}$), mesophiles ($20-45\,^\circ\text{C}$), thermophiles ($50-80\,^\circ\text{C}$), and hyperthermophiles ($80-110\,^\circ\text{C}$).

Psychrophile

A microorganism that exhibits optimal growth in cold temperatures between $0\,^\circ\text{C}$ and $20\,^\circ\text{C}$.

Mesophile

A microorganism adapted to moderate temperatures, showing optimal growth between $20\,^\circ\text{C}$ and $45\,^\circ\text{C}$.

Thermophile

A microbe that prefers hot environments, growing optimally between $50\,^\circ\text{C}$ and $80\,^\circ\text{C}$.

Hyperthermophile

An extreme heat-loving microbe with optimal growth between $80\,^\circ\text{C}$ and $110\,^\circ\text{C}$.

Microbial Osmotic Salt Responses

Prokaryotic growth classifications by optimum salt concentration: non-halophile ($<1\%$), slight halophile ($1.7-4.8\%$), moderate halophile ($4.7-20\%$), and extreme halophile ($20-30\%$).

Halophile

A microorganism that requires elevated sodium chloride ($\text{NaCl}$) concentrations for growth.

Non-halophile

A microbe that grows best at low salt concentrations below $1\%$ and is inhibited by elevated salinity.

Thioglycolate medium

A specialized liquid growth medium used to test microbial oxygen requirements by establishing a vertical oxygen concentration gradient.

Anaerobic chamber

An enclosed chamber that uses chemical packets to remove oxygen to near-zero levels, allowing culturing of obligate anaerobes.