Biomedical Microbiology VTPB 504 – Laboratory Practical Vocabulary

A comprehensive vocabulary set covering safety, microscopy, staining, media, biochemical tests, hemolysis, virology, mycology, parasitology, growth requirements, antibiotic susceptibility, and immunoassays discussed in the VTPB 504 laboratory practical review.

Turret (Revolving Nosepiece)

Holds objective lenses (4×, 10×, 40×, 100×) and allows rotation to change magnification.

Stage

Platform that supports the microscope slide for observation.

Mechanical Stage Control Knobs

Move the microscope stage horizontally and vertically to view different slide areas.

Eyepiece / Ocular Lens

Lens you look through; usually 10× magnification.

Condenser

Lens system beneath the stage that focuses light onto the specimen.

Iris Diaphragm

Adjustable aperture that regulates light intensity and contrast.

Coarse Focus Knob

Raises or lowers stage rapidly for rough focusing.

Fine Focus Knob

Moves stage slightly for sharp, detailed focusing.

Köhler Illumination

Microscope light-setting method producing even, glare-free illumination.

Oil Immersion Lens (100×)

High-power objective requiring immersion oil to reduce light diffraction.

Smear Preparation

Process of spreading, air-drying, and heat-fixing cells on a slide for staining.

Air Drying

Removing moisture from smear at body temperature before heat fixation.

Heat Fixation

Heating dried smear to adhere cells to glass and kill organisms.

Simple Stain

Single dye (e.g., crystal violet) that colors all cells uniformly to show shape and size.

Differential Stain

Staining method (e.g., Gram stain) that distinguishes cell types or structures.

Gram-Positive Cell Wall

Thick peptidoglycan layer retaining crystal violet; appears purple after Gram stain.

Gram-Negative Cell Wall

Thin peptidoglycan layer; loses crystal violet, picks up safranin; appears pink.

Acid-Fast Organism

Bacterium with mycolic acid-rich wall resisting ordinary stains (e.g., Mycobacterium).

Ziehl–Neelsen Stain

Heat-assisted acid-fast stain using carbol-fuchsin, acid alcohol, and methylene blue.

Kinyoun Stain

Cold acid-fast stain using detergent (Tergitol) instead of heat.

Capsule Stain

Negative stain highlighting clear capsules around cells against a colored background.

Endospore Stain

Uses malachite green (with heat) and safranin to show green spores in red cells.

Liquid Medium (Broth)

Growth medium lacking agar; used for propagation of microbes.

Solid Medium

Broth solidified with agar for colony isolation.

Inoculating Loop

Wire instrument for transferring cultures, streaking plates, or inoculating broths.

Inoculating Needle

Straight wire used to stab deep media (e.g., motility, TSIA).

Aseptic Technique

Procedures preventing contamination of cultures, self, and environment.

Streak for Isolation

Quadrant streak method to dilute bacteria and obtain single colonies.

Selective Medium

Culture medium containing inhibitor(s) that suppress unwanted microbes, allowing others.

Differential Medium

Medium containing indicator(s) revealing metabolic differences without inhibition.

Selective/Differential Medium

Medium with both inhibitors and indicators (e.g., MacConkey agar).

Phenol Red Carbohydrate Broth

Broth with phenol red pH indicator and single sugar to test fermentation.

Durham Tube

Small inverted vial in broth to collect gas produced by microbes.

TSIA (Triple Sugar Iron Agar)

Slant/butt medium testing glucose, lactose, sucrose use, gas, and H₂S production.

K/A Reaction

Red slant/yellow butt in TSIA indicating glucose fermentation only.

A/A+G Reaction

Yellow slant & butt with cracks showing fermentation of multiple sugars and gas.

K/N Reaction

Red slant/no change butt; obligate aerobe, no fermentation.

Nitrate Reductase

Enzyme reducing nitrate to nitrite in nitrate test.

Nitrite Reductase

Enzyme further reducing nitrite to nitrogen gas or ammonia.

Urease

Enzyme hydrolyzing urea to ammonia and CO₂; turns urea broth hot pink.

Motility Test

Semi-solid medium with tetrazolium salt assessing bacterial flagellar movement.

Catalase

Enzyme decomposing H₂O₂ to water and O₂; bubbles indicate positive test.

Coagulase

Extracellular protein causing rabbit plasma to clot; indicates pathogenic Staphylococcus.

Mannitol Salt Agar (MSA)

High-salt selective/differential medium; mannitol fermenters turn agar yellow.

Novobiocin Test

Disk assay; resistance presumptively identifies Staphylococcus saprophyticus.

Bacitracin Test

Disk assay; susceptibility presumptively identifies Streptococcus pyogenes.

Optochin Test

Disk assay; susceptibility presumptively identifies Streptococcus pneumoniae.

Bile Esculin Agar

Selective/differential medium; growth + blackening indicates enterococci hydrolyzing esculin.

CAMP Factor

Protein from Streptococcus agalactiae enhancing S. aureus hemolysis forming arrowhead.

Streptocard Test

Latex agglutination for Lancefield grouping of Streptococcus cell-wall carbohydrates.

RapID ONE System

Commercial panel of micro-tubes for rapid biochemical ID of oxidase-negative Enterobacteriales.

Relative Microbe Sizes

Order: viruses < bacteria < fungi < parasites (largest).

Hemolysin

Bacterial factor lysing red blood cells for iron acquisition.

Gamma Hemolysis

No hemolysis on blood agar; media remains unchanged.

Beta Hemolysis

Complete clearing around colonies due to total RBC lysis.

Alpha Hemolysis

Partial hemolysis giving greenish discoloration (methemoglobin).

Double Zone Hemolysis

Two concentric hemolysis zones from different enzymes (e.g., Clostridium perfringens).

Oxidase Test

Detects cytochrome c oxidase; purple color within seconds is positive.

MacConkey Agar

Bile salt/crystal violet selective medium; lactose fermenters yield pink colonies.

Eosin Methylene Blue (EMB) Agar

Selective/differential agar; E. coli shows green metallic sheen from strong lactose fermentation.

Salmonella-Shigella (SS) Agar

Selective/differential; non-lactose colonies are colorless; H₂S producers have black centers.

Indole Test

Detects indole from tryptophan using Kovac’s reagent; red ring = positive.

Methyl Red Test

Detects stable mixed acids; red color at pH <4.5 is positive.

Voges-Proskauer Test

Detects acetoin (2,3-butanediol pathway); red after VP reagents = positive.

Citrate Utilization Test

Blue slant indicates organism can use citrate as sole carbon source.

Lysine Decarboxylase (LDC)

Enzyme removing CO₂ from lysine, producing alkaline cadaverine (purple butt).

Lysine Deaminase (LDA)

Enzyme deaminating lysine; slight acid makes slant port-wine color.

Lysine Iron Agar (LIA)

Slant/butt medium testing LDA/LDC and H₂S production.

Ornithine Decarboxylase Broth

Medium testing ODC; purple after alkaline putrescine formation is positive.

Putrescine

Alkaline product of ornithine decarboxylation raising pH.

Bacteriophage

Virus that infects bacteria; forms plaques in lawn cultures.

Plaque

Clear zone on bacterial lawn where phage lysed host cells.

PFU (Plaque-Forming Unit)

Measure of infectious virions; plaques × dilution factor / volume gives PFU / mL.

Yeast

Unicellular fungus reproducing mainly by budding.

Mold

Multicellular fungus composed of hyphae forming mycelium; reproduces via spores.

Dimorphic Fungus

Fungus existing as yeast or mold depending on conditions.

Sabouraud Dextrose Agar (SDA)

Acidic medium favoring fungal growth; often with antibiotics.

Dermatophyte Test Medium (DTM)

Medium detecting skin-infecting fungi; alkaline waste turns agar red.

Aspergillus species

Septate mold with bulbous vesicle and radiating conidiospores; respiratory pathogen.

Penicillium species

Septate mold with branching “paintbrush” conidiophore; source of penicillin.

Candida species

Yeast; mucosal commensal that can overgrow after antibiotics.

Malassezia species

Lipophilic yeast on skin; causes opportunistic infections.

Diff-Quick Stain

Rapid three-step stain (methanol, eosin, methylene blue) for cytology and fungi.

Parasite

Organism living on/in host, deriving nutrients at host’s expense.

Definitive Host

Host in which parasite reaches sexual maturity.

Intermediate Host

Host harboring immature or asexual stages of parasite.

Zoonotic Disease

Illness transmissible from animals to humans.

Direct Life Cycle

Parasite completes development in a single host species.

Indirect Life Cycle

Parasite requires multiple hosts to complete development.

Bacterial Growth Curve

Phases: lag, log, stationary, death; measured via optical density.

Obligate Aerobe

Organism that must use O₂ for respiration; cannot grow anaerobically.

Obligate Anaerobe

Organism killed or inhibited by O₂; relies on fermentation only.

Facultative Anaerobe

Grows with or without O₂; can switch between respiration and fermentation.

Aerotolerant Anaerobe

Uses fermentation exclusively but tolerates O₂.

Microaerophile

Requires low O₂ concentration for growth; higher levels toxic.

Capnophile

Microbe that grows best at elevated CO₂ levels.

Fluid Thioglycollate Medium

Semi-solid medium with reducing agent creating O₂ gradient to study aerotolerance.

Gas-Pak Anaerobic Jar

Sealed container generating H₂ and CO₂ to remove O₂ for anaerobe cultivation.

Kirby-Bauer Test

Standard disk diffusion assay measuring antimicrobial susceptibility by zone sizes.

MacFarland Standard

Turbidity reference (e.g., 0.5) to standardize inoculum density in susceptibility tests.