(6) Flashcards
a contrast with the background of the microscope field
contrast
the shape of an organism; determining cell morphology is an important first step in identifying a bacterial species
morphology
spherical cell
cocci (coccus)
rod-shaped cell
bacilli (bacillus)
spiral-shaped cell
spirilla (spirillum)
slightly curved rods
vibrios
short rods
coccobacillus
flexible spirals; flexible, curved rods
spirochetes
where a variety of cell shapes-slender, ellipsoidal, or ovoid rods- may be seen in a given sample
pleomorphism
formed if the two daughter cells remain attached after a coccus divides; have a single division plane and the cells generally occur in pairs
diplococcus
formed if the two daughter cells remain attached after a coccus divides
diplobacilli
an arrangement resulting from cells that continue to divide in the same plane and remain attached; single division plane, but the cells remain attached to form chains of variable length
streptococcus
an arrangement resulting from cells that continue to divide in the same plane and remain attached
streptobacilli
a cluster of cells is produced to form a staphylococcus if the division planes of a coccus are irregular; divide in more than three planes to produce a characteristic grape-like cluster of cells
staphylococcus
a colored molecule (often a benzene derivative)
chromogen
the charged region of a dye molecule that gives it its color; the portion of the chromogen that gives it its color
chromophore
the charged portion of a chromogen and allows it to act as a dye through ionic or covalent bonds between the chromogen and the cell
auxochrome
staining solution with a negatively charged chromophore
acidic stains
staining solution with a positively charged chromophore; where the auxochrome becomes positively charged as a result of picking up a hydrogen ion or losing a hydroxide ion; attracted to the negative charges on the surface of most bacterial cells
basic stains
kills the bacteria, makes them adhere to the slide, and coagulates cytoplasmic proteins to make them more visible.
heat-fixed emulsion
How does a basic stain work?
The auxochrome becomes positively charged as a result of picking up a hydrogen ion or losing a hydroxide ion. They are attracted to the negative changes on the surface of most bacterial cells. Thus, the cell becomes colored.
List 3 common basic stains.
Methylene blue, crystal violet and safranin
Why must a sample be heat-fixed?
To kill the bacteria, make them adhere to the slide, and coagulate cytoplasmic proteins to make them more visible.
What is the chemical property of the chromogen (dye) used in a negative stain?
The chromogen is acidic and carries a negative charge. (An acidic chromogen gives up a hydrogen ion, which leaves it with a negative charge).
Explain why only the background is stained when performing a negative stain.
The negative charge on the bacterial surface repels the negatively charged chromogen, so the cell remains unstained against a colored background.
What stain was used in the negative stain procedure performed in class?
Nigrosin or eosin stain
What color was the cell after negative staining?
Unstained
