Practicum #1 Microbio Lab

Vocabulary flashcards covering microbiology laboratory skills, aseptic techniques, isolation streaking methods, specialized and differential staining (Gram, spore, capsule, negative), selective/differential media, biochemical identification tests, and microscope anatomy and optical principles.

Pure Culture

A microbial culture that contains only a single species of microorganism.

Mixed Culture

A microbial culture consisting of two or more distinct microbial species.

Colony-Forming Unit (CFU)

A descriptive term for the origin of a bacterial colony, recognizing that colonies can arise from single cells, pairs, chains, or clusters of cells.

Streak Plate Method

An isolation procedure in which a microbial sample is systematically spread across an agar surface to reduce cell density and obtain isolated colonies.

Quadrant Streak

An inoculation pattern performed on an agar plate across four sections with flame sterilizations between each, primarily used to isolate species from mixed cultures with suspected high cell density.

T-Streak Method

A variation of the streak plate technique in which the base of the agar plate is divided into three regions using a "T" guideline to dilute and isolate high-density bacterial samples.

Zigzag (Continuous) Inoculation

An inoculation method where a sample is streaked continuously back and forth across an agar plate using a swab or loop, used for samples with lower cell density or pure cultures where colony isolation is unnecessary.

Aseptic Technique

A set of procedures designed to prevent microbial contamination of cultures, sterile media, and the laboratory environment by creating a sterile barrier between the working area and external sources of microbes.

Subculturing

The microbiological practice of transferring microorganisms from one culture medium to a fresh, sterile medium to maintain stocks or perform diagnostic testing.

Capsule

A structural layer of polysaccharides and proteins secreted by bacteria that adheres firmly to the cell wall, protecting against dehydration, trapping nutrients, and evading phagocytosis by white blood cells.

Slime Layer

A thin, unorganized, and loosely attached flowing glycocalyx layer secreted on the outer surface of certain bacterial cells.

Glycocalyx

A general comprehensive term referring to extracellular surface matrices produced by bacteria, encompassing both capsules and slime layers.

Endospore

A dormant, highly resistant cellular structure containing minimal water formed by genera such as Bacillus and Clostridium that can survive extreme conditions, including boiling water for two hours or more.

Schaeffer-Fulton Method

A differential spore-staining procedure that utilizes steam heat to force 5% malachite green into resistant endospores, followed by water rinsing and counterstaining vegetative cells with safranin.

Chromogen

The colored molecule in a biological stain (typically a benzene derivative) that consists of a chromophore and an auxochrome.

Chromophore

The specific chemical portion of a chromogen molecule that absorbs and reflects distinct wavelengths of light to produce visible color.

Auxochrome

The charged functional group of a chromogen that acts as an anchor, allowing the dye to form ionic or covalent bonds with target bacterial structures.

Basic Stain

A microbiological stain with a positively charged auxochrome that readily binds to the negatively charged surface structures of bacterial cells.

Negative Stain

A staining procedure using an acidic dye with a negatively charged chromogen (such as nigrosin or India ink) that repels bacterial surfaces, coloring the background dark while leaving unfixed cells transparent.

Heat Fixing

The laboratory procedure of briefly passing an air-dried bacterial smear over a flame to kill the organisms, adhere cells firmly to the glass slide, and coagulate cytoplasmic proteins to enhance dye uptake.

Gram Stain

A four-step differential staining procedure discovered by Christian Gram in 1884 that separates bacteria into gram-positive and gram-negative groups based on the structural thickness of their peptidoglycan cell wall.

Mordant

A substance, such as Gram's iodine, that enhances dye retention by forming an insoluble chemical complex with the primary stain inside bacterial cells.

Decolorizer (Gram Stain)

$95\%$ ethyl alcohol, which extracts the crystal violet-iodine complex from thin-peptidoglycan, lipid-rich gram-negative cell walls while dehydrating thick peptidoglycan in gram-positive cell walls to retain the color.

Safranin

A red basic counterstain used in the Gram stain to color decolorized gram-negative bacteria pink or red, as well as in the endospore stain to color vegetative cells.

Bacterial Cellular Arrangements (Cocci)

Morphological patterns of spherical bacteria, including streptococci (chains), staphylococci (irregular clusters), and diplococci (pairs).

Phenylethyl Alcohol Agar (PEA)

A selective growth medium that permits the growth of gram-positive cocci while inhibiting most gram-negative organisms, specifically Proteus species.

Mannitol Salt Agar (MSA)

A selective and differential medium containing high salt to select for Staphylococcus species, mannitol for fermentation, and phenol red to indicate acid production by changing to yellow.

MacConkey Agar

A selective and differential medium designed to isolate gram-negative enteric bacilli and differentiate lactose fermenters (pink/red colonies) from lactose non-fermenters.

Coagulase Test

A biochemical test that differentiates Staphylococcus aureus (coagulase-positive, causing plasma clotting) from coagulase-negative staphylococci such as S. epidermidis and S. saprophyticus.

Triple Sugar Iron (TSI) Agar

A multi-test differential slant medium containing glucose, lactose, sucrose, and iron to assess carbohydrate fermentation, gas production, and $\text{H}_2\text{S}$ sulfur reduction.

Citrate Utilization Test

A component of the IMViC test series that evaluates whether an organism can use sodium citrate as its sole carbon source and possess citrate permease, changing Simmons citrate agar from green to blue.

Enterotube II

A multi-compartment rapid identification system containing 12 distinct biochemical media used to identify unknown oxidase-negative, gram-negative bacilli of the family Enterobacteriaceae.

Kirby-Bauer Method

A standardized agar disc-diffusion method for testing antibiotic susceptibility, in which zones of inhibition around paper antimicrobial discs are measured to classify bacterial resistance or sensitivity.

RapID ONE Panel

A qualitative micro-method system that uses conventional and chromogenic substrates to rapidly identify medically important gram-negative bacteria.

Compound Light Microscope

An optical instrument utilizing an illumination source and multiple lens systems (ocular and objective) to magnify microbiological specimens up to $1{,}000\times$.

Total Magnification

The complete magnification of a compound microscope, calculated by multiplying the power of the objective lens by the power of the ocular lens ($\text{Total Magnification} = \text{Objective} \times \text{Ocular}$).

Working Distance

The linear clearance distance between the anterior front lens of an objective and the surface of the microscope slide cover glass when the specimen is in sharp focus.

Condenser

A non-magnifying optical lens system positioned directly beneath the microscope stage that gathers and concentrates light rays into a cone focused onto the specimen.

Iris Diaphragm Lever

A control lever connected to a shutter assembly within the condenser that adjusts the diameter of the light cone to control brightness and enhance image contrast.

Parfocal

An optical property of modern microscope objective lenses whereby a specimen brought into focus under one objective remains essentially in focus when switching to another objective.