Microbiology Lab Techniques – Chapter 3 Vocabulary

Vocabulary flashcards covering key microbiology lab terms from Chapter 3, including media types, the Five I’s workflow, culture techniques, and diagnostic concepts.

Five I’s

The core steps in the microbiology lab—Inoculation, Incubation, Isolation, Inspection, and Identification—used to obtain and analyze pure cultures.

Inoculation

Introduction of a sample (e.g., a swab) onto or into a growth medium to begin culturing microorganisms.

Incubation

Keeping inoculated media at controlled temperature and atmospheric conditions to promote microbial growth (commonly 20-45 °C).

Isolation

Separating individual microbes on solid media so that discrete colonies arise from single cells.

Inspection

Observing colony morphology (color, size, shape, odor) or microscopic appearance to gather preliminary data about an organism.

Identification

Final determination of a microbe’s species or genus using stains, biochemical tests, immunologic assays, genetics, or other methods.

Culture / Culturing

Growing microorganisms in the laboratory to increase their numbers for observation or testing.

Medium (pl. Media)

A nutrient-containing environment (liquid, semi-solid, or solid) used to grow microorganisms.

Sterile

Free of all life forms—including spores and viruses—so no unwanted microbes contaminate a culture.

Incubator

Laboratory device that maintains set temperature, humidity, and gas levels to support microbial growth.

Agar

Complex polysaccharide from red algae that solidifies media; melts at ~100 °C and solidifies around 45 °C.

Tryptic Soy Agar (TSA)

General-purpose solid medium that supports growth of a wide variety of bacteria.

Mannitol Salt Agar (MSA)

Both selective (high salt favors staphylococci) and differential (mannitol fermentation turns the medium yellow) medium for Staphylococcus species.

Selective Media

Media containing agents that inhibit some microbes while allowing others to grow, e.g., gram-positive-only plates.

Differential Media

Media that allow multiple microbes to grow but reveal visible differences (color, colony appearance) to distinguish them.

Enrichment Media

Media supplemented with extra nutrients (vitamins, amino acids, blood) to encourage growth of fastidious organisms.

Synthetic (Defined) Media

Growth media whose exact chemical composition is known and quantified.

Complex Media

Media containing at least one component of unknown composition (e.g., yeast extract, blood); exact chemicals not fully defined.

Blood Agar

Enriched and differential medium containing sheep’s blood; used to detect hemolysis patterns.

Hemolysin

Bacterial enzyme or toxin that lyses red blood cells, producing clear zones on blood agar.

Alpha Hemolysis

Partial (greenish) lysis of red blood cells around colonies on blood agar.

Beta Hemolysis

Complete clearing of red blood cells around colonies on blood agar; indicates strong hemolysis.

Gamma Hemolysis

No hemolysis; red blood cells remain intact around colonies on blood agar.

Streak Plate Method

Technique of dragging an inoculating loop across agar in quadrants to dilute and isolate single colonies.

Zone of Inhibition

Clear area around microbial growth or antibiotic disks where bacteria have been lysed or cannot grow.

Aerobic Bacteria

Microbes that require oxygen for growth and metabolism.

Anaerobic Bacteria

Microbes that grow without, or are killed by, atmospheric oxygen.

Phenotypic Testing

Identification approach based on observable traits such as morphology, staining, enzyme activity, or metabolism.

Immunologic Testing

Detection of microbes via specific antigen–antibody interactions (e.g., rapid strep test, ELISA).

Macroscopic Analysis

Examination of colonies or cultures with the naked eye for size, color, texture, and patterns.

Microscopic Analysis

Observation of stained or live microorganisms under a microscope to study cell shape, arrangement, and structures.

Gram-Positive Bacteria

Bacteria with thick peptidoglycan cell walls that retain crystal violet stain, appearing purple after Gram staining.

Gram-Negative Bacteria

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

Myo­bacterium tuberculosis

Slow-growing acid-fast bacterium; culture can require up to a month to produce visible colonies.

Poliovirus

One of the smallest known viruses (~30 nm), often cited when discussing viral size ranges.