Gram Staining, Lab Terms and Microorganisms

Vocabulary flashcards based on lecture notes covering Gram staining, bacterial morphology, infection types, epidemiology, and fundamental microbiology lab equipment.

Gram-positive cell wall

A cell wall characterized by a single, thick layer of peptidoglycan ($20-80\,nm$) associated with teichoic acids that retains crystal violet stain.

Gram-negative cell wall

A cell wall consisting of two layers: a thin layer of peptidoglycan ($8-10\,nm$) and an outer membrane, with an encompassing periplasmic space.

Crystal violet

The primary stain in the Gram staining procedure that stains all bacteria purple.

Gram’s iodine

The mordant in Gram staining that joins with crystal violet to form large molecules that become trapped in the peptidoglycan layer.

Acetone alcohol

The decolorizer that removes the stain from Gram-negative cell walls while leaving Gram-positive cells purple.

Safranin

The counterstain used to add color (red/pink) to the Gram-negative cells that were rendered colorless by the decolorizer.

Peptidoglycan

A cell wall component made of N-acetylglucosamine and N-acetylmuramic acid; its synthesis is inhibited by antibiotics like penicillin.

Lipopolysaccharide (LPS)

A chemical component found in the outer membrane of Gram-negative bacteria.

Porins

Proteins present in the outer membrane of Gram-negative bacteria that affect the permeability of molecules.

Coccus

A spherical-shaped bacterium; subtypes include Streptococcus, Staphylococcus, Diplococcus, Tetrad, and Sarcina.

Bacillus

A rod-shaped bacterium; subtypes include Diplobacillus, Streptobacillus, and Coryneform.

Spirochete

A long, thin, flexible spiral-shaped bacterium.

Transmissible

An infectious disease agent that is transmitted from a reservoir or portal of exit to another host’s portal of entry.

Fomites

Inanimate objects (e.g., needles, toothbrushes, drinking glasses) that facilitate indirect contact transmission of pathogens.

Droplet Transmission

The spread of pathogens via mucus droplets that exit the mouth or nares during exhaling, coughing, or sneezing.

Vehicle Transmission

The spread of pathogens via air, drinking water, and food, as well as blood and body fluids handled outside the body.

Biological Vectors

Biting arthropods, such as mosquitoes, ticks, lice, fleas, and mites, that transmit diseases between hosts.

Mechanical Vectors

Animals, like houseflies and cockroaches, that passively carry pathogens to new hosts on their feet or other body parts.

Epidemic

The appearance of an infectious disease or condition that attacks many people at the same time in the same geographical location.

Pandemic

An epidemic that occurs simultaneously on more than one continent (e.g., AIDS, COVID-19).

Endemic

A disease peculiar to and recurring continuously in a particular locality or population, such as Histoplasmosis-Ohio Valley.

Contagious

A communicable disease that is easily transmitted from a reservoir or person, such as the common cold.

Epidemiology

The study of the occurrence, distribution, and spread of disease in humans.

Incidence

The number of new cases of a disease in a given area or population during a given period of time.

Prevalence

The total number of cases, including both new and existing cases, in a given area or population during a given period of time.

Broth

A liquid medium containing various nutrients used to culture bacteria and other microorganisms.

Agar

A gelatinous material derived from algae used as a culture medium; it remains firm up to $65^\circ\text{C}$ and melts at approximately $85^\circ\text{C}$.

Hysteresis

The property of agar where it melts at a much higher temperature ($85^\circ\text{C}$) than the temperature at which it solidifies ($32-40^\circ\text{C}$).

Deep

A culture where inoculation is made deep into a solid medium, used especially for the growth of anaerobic bacteria.

Slant

A culture made on the slanting surface of a solidified medium in a test tube tilted to provide a greater growth area.

Plates

Petri dishes containing solid growth medium (typically agar plus nutrients) used to culture microorganisms.

Incubation

The act of maintaining controlled environmental conditions to favor the growth or development of microbial cultures.

Colony

A visible mass of microorganisms originating from a single mother cell, constituting a clone of genetically alike bacteria.

Loop

A simple tool used to retrieve an inoculum from a culture and transfer it for cultivation or streaking on plates.

Needles

Tools used in microbiology to transfer and inoculate living microorganisms, often into deeps.

Bunsen Burner

A small adjustable gas burner used to provide a flame in the laboratory.