MICRO 2042 Practical #1 Study Guide

Comprehensive vocabulary flashcards generated directly from the MICRO 2042 Practical #1 Study Guide transcript.

Mannitol Salt Agar (MSA)

A selective and differential culture medium containing 7.5% sodium chloride as an inhibitor and phenol red as an indicator; selects for salt-tolerant organisms (especially Staphylococcus species) and turns yellow upon positive mannitol fermentation.

MacConkey agar

A culture medium selective for Gram-negative bacteria (inhibiting Gram-positive) and differential for lactose fermentation using neutral red as an indicator, turning pink/red for lactose fermenters and remaining clear/colorless for non-fermenters.

CNA agar

A selective culture medium for Gram-positive bacteria that uses colistin and nalidixic acid as inhibitors against Gram-negative organisms.

Blood agar

An enriched and differential medium used to observe bacterial hemolysis.

Mueller-Hinton agar

The standard culture medium used for susceptibility testing, such as the Kirby-Bauer disk diffusion assay.

Alpha hemolysis

Partial red blood cell destruction on blood agar, typically producing a greenish discoloration around the bacterial colony.

Beta hemolysis

Complete red blood cell destruction on blood agar, producing a clear/transparent zone around the colony.

Gamma hemolysis

No visible hemolysis and no visible change in the blood agar surrounding the colony.

Clostridium sporogenes

A bacterium classified for this practical as an obligate anaerobe that grows in an anaerobic box or at the bottom of thioglycollate tubes, but not under normal atmospheric oxygen conditions.

Obligate aerobe

An organism requiring oxygen for growth, exhibiting growth at the top of a thioglycollate tube where oxygen concentration is highest.

Obligate anaerobe

An organism to which oxygen is harmful or strongly inhibitory, growing at the bottom of a thioglycollate tube where oxygen concentration is lowest.

Facultative anaerobe

An organism capable of growing throughout a thioglycollate tube, though growth is heavier near the top.

Aerotolerant anaerobe

An organism that shows relatively even growth throughout a thioglycollate tube regardless of oxygen presence.

Microaerophile

An organism that grows in a thin band just below the surface of a thioglycollate tube where oxygen concentration is lower than atmospheric levels.

Total magnification

Calculated by multiplying ocular magnification by objective magnification (e.g., $10\times$ ocular $\times 100\times$ objective = $1000\times$).

Condenser

A component of a microscope that focuses light through the specimen.

Diaphragm

A microscope part that controls the amount of light passing through the specimen.

Resolution

The ability to distinguish two close objects as separate entities.

Gram stain procedure

A four-step differential staining order consisting of crystal violet (primary stain), iodine (mordant), alcohol (decolorizer), and safranin (counterstain), coloring Gram-positive cells purple and Gram-negative cells pink/red.

Negative stain

A technique using nigrosin to show true cell size, shape, and arrangement without heat-fix distortion because both the stain and bacterial cell surface carry a negative charge.

Kirby-Bauer disk diffusion

A test used to determine bacterial antibiotic susceptibility by applying antibiotic disks onto a bacterial lawn on Mueller-Hinton agar and measuring zones of inhibition.

Zone of inhibition

The clear area around an antibiotic disk on a culture plate where bacterial growth is inhibited.

Bactericidal

Refers to an agent or substance that kills bacteria.

Bacteriostatic

Refers to an agent or substance that inhibits bacterial growth and reproduction without necessarily killing them.

Minimum Inhibitory Concentration (MIC)

The lowest concentration of an antimicrobial agent that prevents visible bacterial growth, which can be measured using an E-test gradient strip.

Agar

A solidifying agent used to prepare solid culture media (present at 0% concentration in liquid broth).

Selective media

Media designed to inhibit certain microorganisms while favoring the growth of others.

Differential media

Media designed to distinguish between different organisms based on visible biochemical or growth reactions.

Complex medium

A nutrient medium in which the exact chemical composition is not completely defined.

Defined medium

A nutrient medium in which all chemical components and their exact concentrations are known.

Phototroph

An organism that derives its energy from light.

Chemotroph

An organism that derives its energy from chemical compounds.

Autotroph

An organism that obtains carbon from $\text{CO}_2$ or other inorganic carbon sources.

Heterotroph

An organism that obtains carbon from organic compounds.

Acid-fast stain procedure

A differential staining technique using carbolfuchsin (primary stain), acid-alcohol (decolorizer), and methylene blue (counterstain), staining acid-fast cells red/pink and non-acid-fast cells blue.

Mycolic acids

Waxy lipids found in the cell walls of Mycobacterium species that make them difficult to stain with standard stains.

Psychrophile

An organism that thrives in cold temperatures.

Mesophile

An organism that thrives in moderate temperatures; includes many human-associated organisms.

Thermophile

An organism that thrives in high temperatures.

Hyperthermophile

An organism that thrives in extremely high temperatures.

Thermal death time

The time required to kill all microorganisms in a sample at a specified temperature and set of conditions.

Thermal death point

The lowest temperature that kills all microorganisms in a sample within a specified time.

D-value

The time at a specific temperature required to reduce a microbial population by $90\%$, or one log unit.

Autoclaving

A microbial control method relying on pressure, temperature, and time; standard conditions are about $121\,^\circ\text{C}$ at $15\,\text{psi}$ for roughly $15\text{--}20\,\text{minutes}$.

UV-C

The ultraviolet wavelength range with peak germicidal effectiveness around $260\,\text{nm}$, which damages DNA by creating pyrimidine/thymine dimers.

Photolyase

An enzyme capable of repairing UV-induced thymine dimers during photoreactivation.

Acidophile

An organism that prefers acidic growth conditions.

Neutrophile

An organism that prefers near-neutral pH growth conditions.

Alkaliphile

An organism that prefers alkaline/basic growth conditions.

Osmosis

The movement of water across a selectively permeable membrane toward the side with greater effective solute concentration.

Halophile

An organism that requires high salt concentrations for growth, such as H. salinarum.

Halotolerant

An organism that tolerates high salt conditions but does not require them.

Antiseptic

An antimicrobial chemical intended for application on living tissue.

Disinfectant

An antimicrobial chemical intended for application on nonliving surfaces.

Sterilization

The complete removal or destruction of all forms of microbial life, including endospores.

Sanitization

The reduction of microbial populations to levels deemed safe by public-health standards.

Catalase test

A test using hydrogen peroxide ($\text{H}_2\text{O}_2$) to detect the enzyme catalase, yielding bubbles via the reaction $2\text{H}_2\text{O}_2 \rightarrow 2\text{H}_2\text{O} + \text{O}_2$ (Staphylococcus is usually positive; Streptococcus/Enterococcus are usually negative).

Mycology

The study of fungi, which are organisms in domain Eukarya.

Dimorphic fungus

A fungus that can exist in two distinct structural forms depending on environmental conditions.

Lichen

A symbiotic association between a fungus (providing structure, protection, water/minerals) and a photosynthetic partner such as a green alga or cyanobacterium (providing organic nutrients).

Prodigiosin

A red pigment produced by Serratia marcescens, often more visible at cooler/room temperatures than at $37\,^\circ\text{C}$.

Eosin Methylene Blue (EMB) agar

A medium selective for Gram-negative bacteria and differential for lactose fermentation.

Coliforms

Gram-negative rods that are typically lactose-fermenting, often facultative anaerobes, and used as indicators of water quality.

Escherichia coli

A bacterial species serving as a major indicator organism for fecal contamination in water quality testing.