Gram Staining, Lab Terms and Microorganisms

A set of practice flashcards covering Gram staining, lab terms, infection terminology, and microbiology concepts.

What distinguishes Gram-positive from Gram-negative bacteria in their cell walls?

Gram-positive have a thick peptidoglycan layer with teichoic acids that traps crystal violet; Gram-negative have a thin peptidoglycan layer plus an outer membrane with LPS and a periplasmic space.

What component is characteristic of Gram-positive cell walls that helps retain crystal violet?

Teichoic acids (along with a thick peptidoglycan layer).

What components differentiate Gram-negative cell walls?

An outer membrane with lipopolysaccharide (LPS), a periplasmic space, and a thinner peptidoglycan layer.

Name the four reagents used in the Gram stain and their roles.

Crystal violet (primary stain), Gram’s iodine (mordant), acetone-alcohol (decolorizer), safranin (counterstain).

List the steps in the Gram staining procedure.

1) Apply primary stain; 2) Apply mordant; 3) Decolorize with acetone/alcohol; 4) Apply counterstain; rinse between steps.

What color do Gram-positive and Gram-negative bacteria typically appear after the final Gram stain?

Gram-positive cells remain purple; Gram-negative cells become colorless and then appear red after counterstaining.

What is the function of Gram’s iodine in the Gram stain?

Mordant that binds crystal violet to form larger complexes trapped in the cell wall.

What does the decolorizer (acetone-alcohol) do during Gram staining?

Decolorizes Gram-negative cells by removing outer membrane and some stain; Gram-positive retain crystal violet.

What is the purpose of the counterstain (safranin) in Gram staining?

Colorizes the decolorized Gram-negative cells so they appear red/pink.

What is a bacterial colony?

A visible mass of microorganisms arising from a single cell, representing a clone.

What is a broth in microbiology?

A liquid culture medium used to grow microorganisms.

What is agar and why is it used?

A gel-like solid medium derived from algae used to culture microorganisms; solid at room temperature; melts at ~85°C and solidifies around 32–40°C (hysteresis).

What is a slant culture?

A culture grown on the slanted surface of solidified agar in a test tube to maximize surface area for growth.

What is a plate in microbiology?

A Petri dish containing solid agar used to culture microorganisms.

What is incubation in microbiology?

Maintaining controlled environmental conditions to promote growth of microbial cultures.

What is a colony in microbiology?

A visible mass of microorganisms derived from a single progenitor cell.

What are loops and needles used for in the lab?

Tools to transfer and inoculate microorganisms; loops for streaking, needles for inoculation.

What is cross contamination in the lab?

Unwanted transfer of microorganisms between samples, risking erroneous results.

What is a Bunsen burner used for?

A small adjustable gas burner used to heat media and tools in the lab.

Name common bacterial shapes and arrangements.

Cocci (spherical); bacilli (rods); arrangements include diplococcus, streptococcus, staphylococcus, diplobacillus, tetrad, sarcina; Spirillum, Spirochete, Vibrio, Coryneform.

What is the periplasmic space and where is it located?

The space between the cytoplasmic membrane and the outer membrane in Gram-negative bacteria.

What is Lipopolysaccharide (LPS) and where is it found?

An endotoxin component of the Gram-negative outer membrane that contributes to barrier function and virulence.

Which antibiotics target cell wall synthesis?

Beta-lactams, glycopeptides, and bacitracin.

Which antibiotics target protein synthesis?

Chloramphenicol, macrolides, and aminoglycosides.

Which antibiotics target membrane integrity?

Polymyxins.

Which antibiotics inhibit replication/transcription?

Quinolones and rifampicin.

Which antibiotics inhibit synthesis of essential metabolites?

Sulfonamides and trimethoprim.

What is epidemiology?

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

What are incidence and prevalence?

Incidence: number of new cases in a given area/time; Prevalence: total number of cases (new and existing) in a given area/time.

What is an epidemic, a pandemic, and an endemic disease?

Epidemic: many cases in a specific area; Pandemic: worldwide across continents; Endemic: disease recurring continuously in a locality or population.

What are the modes of transmission for infectious diseases?

Contact (direct/indirect), Droplet, Vehicle (air, water, food, blood/body fluids), Vector (biological and mechanical).

What is foodborne outbreak terminology and give examples?

Outbreaks caused by pathogens like Salmonella, Shigella, E. coli, Staphylococcus aureus, Bacillus cereus, Clostridium botulinum, Clostridium perfringens, Listeria, Norovirus.

What are some benefits of microorganisms (microorganisms as friends)?

Break down food in the gut; produce foods (yogurt, cheese, sauerkraut, wine, bread); produce vitamins, insulin, drugs; decompose waste; recycle nutrients; serve as a food source; manufacture chemicals (acetone, glycerin).

What are some key lab safety concepts mentioned?

Avoid cross contamination; use sterile loops/needles; prepackaged sterile tools; know culture media types and flame/heat sources like Bunsen burners.

What is hysteresis in agar?

A property where agar melts at ~85°C but solidifies at ~32–40°C, allowing it to solidify at room temperature and then be heated for usage.