Lab 4 - Differential stains for bacterial cytology

Question 1

Gram reaction

Answer 1

classify bacteria as Gram-positive (purple) or Gram-negative (pink) based on differences in their cell wall structure. Gram-positive bacteria retain the crystal violet-iodine complex due to their thick peptidoglycan layer, while Gram-negative bacteria lose it and take up the safranin counterstain.

Question 2

primary stain

Answer 2

first applied then chem/physical rxn binds the primary stain to the desired cytological feature

Question 3

counter-stain

Answer 3

stain remaining cells a sharply different colour

Question 4

acid-fast stain

Answer 4

identify bacteria with waxy, lipid-rich cell walls containing mycolic acid (e.g., Mycobacterium). Acid-fast bacteria retain the primary stain (carbol fuchsin) after decolorization with acid-alcohol, appearing red, while non-acid-fast bacteria take up the counterstain (e.g., methylene blue or green).

Question 5

simple stain

Answer 5

A basic stain (e.g., methylene blue, safranin, or crystal violet) used to color all cells in a sample, providing contrast for observing cell shape, size, and arrangement. It is a quick, non-differential staining technique.

Question 6

Schaeffer-Fulton Endospore Stain

Answer 6

A differential stain designed to identify bacterial endospores. Endospores retain the primary stain (malachite green) after heating, while vegetative cells take up the counterstain (safranin). Endospores appear green, and vegetative cells appear red.

Question 7

Differential Capsule Stain

Answer 7

A specialized stain to detect bacterial capsules, which are non-ionic and resist traditional staining. Typically, a negative stain (e.g., India ink) is used to stain the background, while the capsule appears as a clear halo around the stained cell. A counterstain (e.g., crystal violet) may also be applied to color the cells.

Question 8

cytology

Answer 8

the exam of a single cell type, as often found in fluid specimens.