HCC microbiology lab exam 2 Top Scorer Guide
2025 | Real Questions Verified by Experts
Good smears are critical for discerning - the morphology of cells, the arrangement, and
internal structures
What internal structures can you see through staining? - endospores and cell inclusions
What are the goals of staining? - adhere the cells to the slide so they are not washed off
during staining and washing, ensure the shrinkage of cells does not occur, and prepare thin
smears so you can visualize individual cells.
What must be done to bacteria growing on solid media must be what before making a smear? -
diluted using a drop of water
What is the spherical shape of bacteria called? - coccus
What are the rod shape of bacteria called? - cocobacillus, bacillus, fusiform
What are the spiral or curved shape of bacteria called? - vibrio, spirochete, spirillum
What are the shapes of bacterium? - bacilli, cocci, and spiral
Commonly used dyes in simple staining? (basic dyes) - methylene blue, basic fuchsin, and
crystal violet
What is the definition of basic dyes? Why do they bind to bacterial cells? - dyes that have
color bearing ionic groups (chromophores) that are positively charged (cationic). there is an
electrostatic attraction between the negative bacterial cell and the cationic chromophore of the
stain, resulting in stained bacterial cells.
Acidic dyes - dyes that have anionic chromophores (negatively charged). these dyes are
repelled by the bacterial cell and stain the background instead. EXAMPLE: negative stains
palisade arrangement - parallel arrangement of rod-shaped cells (baccili). also calld picket
fence arrangement.
pleomorphism - variations in size and shape among cells of a single species (irregularity
of form)
why are negative stains not normally heat fixed? - to avoid shrinkage of the bacteria. if
the bacteria has a capsule, the structure would be shrinked severely by the heat.
, examples of negative stains - india ink and nigrosin
What does the negative staining procedure consist of? - mixing the organism with a small
amount of stain and spreading a very thin film over the slide.
What are the two methods of negative staining? - spreader method and needle method
What is the goal of the spreader method? - to create a think stain at one end and a thin
stain at the other, creates a perfect thickness in the middle.
What happened in the needle method of negative staining ? - a loop ful of nigrosin is
mixed with the culture rather than a full drop. creates a smaller spread
capsule defintion - distinct and gelatinous layer surrounding the bacteria
slime layer definition - diffuse and irregular layer that surrounds the bacteria.
glycocal - capsule or slime layer that is composed of polysaccarides
What is the capsule layer of bacillus anthracis made of? - composed of a proteinaceous
matrix.
What organism uses a slim layer to prevent phagolytic white blood cells from engulfing and
destroying the pathogen? - Streptococcus pneumoniae
What bacterium causes dental plaque? - Streptococcus mutans- uses its capsule to attach
to the tooth surface
do you heat fix capsule stains? - NOOOOOO it will cause the capsule to shrink
What is the anthony method? - a type of capsular staining. should appear as clear or light
blue halos around the cells, and the cells will be dark purple. staining will occur on the
background because the stains bind to the protein in the background.
What do differential stains take advantage of? - the fact that cells or structures within
cells display dissimilar staining reactions that can be distinguished by use of different dyes.
What is the primary stain in gram staining? - crystal violet (purple)
what is the mordant in gram staining? - iodine
What does iodine do in gram staining? - combines with the crystal violet and forms an
insoluble complex in gram positive cells
2025 | Real Questions Verified by Experts
Good smears are critical for discerning - the morphology of cells, the arrangement, and
internal structures
What internal structures can you see through staining? - endospores and cell inclusions
What are the goals of staining? - adhere the cells to the slide so they are not washed off
during staining and washing, ensure the shrinkage of cells does not occur, and prepare thin
smears so you can visualize individual cells.
What must be done to bacteria growing on solid media must be what before making a smear? -
diluted using a drop of water
What is the spherical shape of bacteria called? - coccus
What are the rod shape of bacteria called? - cocobacillus, bacillus, fusiform
What are the spiral or curved shape of bacteria called? - vibrio, spirochete, spirillum
What are the shapes of bacterium? - bacilli, cocci, and spiral
Commonly used dyes in simple staining? (basic dyes) - methylene blue, basic fuchsin, and
crystal violet
What is the definition of basic dyes? Why do they bind to bacterial cells? - dyes that have
color bearing ionic groups (chromophores) that are positively charged (cationic). there is an
electrostatic attraction between the negative bacterial cell and the cationic chromophore of the
stain, resulting in stained bacterial cells.
Acidic dyes - dyes that have anionic chromophores (negatively charged). these dyes are
repelled by the bacterial cell and stain the background instead. EXAMPLE: negative stains
palisade arrangement - parallel arrangement of rod-shaped cells (baccili). also calld picket
fence arrangement.
pleomorphism - variations in size and shape among cells of a single species (irregularity
of form)
why are negative stains not normally heat fixed? - to avoid shrinkage of the bacteria. if
the bacteria has a capsule, the structure would be shrinked severely by the heat.
, examples of negative stains - india ink and nigrosin
What does the negative staining procedure consist of? - mixing the organism with a small
amount of stain and spreading a very thin film over the slide.
What are the two methods of negative staining? - spreader method and needle method
What is the goal of the spreader method? - to create a think stain at one end and a thin
stain at the other, creates a perfect thickness in the middle.
What happened in the needle method of negative staining ? - a loop ful of nigrosin is
mixed with the culture rather than a full drop. creates a smaller spread
capsule defintion - distinct and gelatinous layer surrounding the bacteria
slime layer definition - diffuse and irregular layer that surrounds the bacteria.
glycocal - capsule or slime layer that is composed of polysaccarides
What is the capsule layer of bacillus anthracis made of? - composed of a proteinaceous
matrix.
What organism uses a slim layer to prevent phagolytic white blood cells from engulfing and
destroying the pathogen? - Streptococcus pneumoniae
What bacterium causes dental plaque? - Streptococcus mutans- uses its capsule to attach
to the tooth surface
do you heat fix capsule stains? - NOOOOOO it will cause the capsule to shrink
What is the anthony method? - a type of capsular staining. should appear as clear or light
blue halos around the cells, and the cells will be dark purple. staining will occur on the
background because the stains bind to the protein in the background.
What do differential stains take advantage of? - the fact that cells or structures within
cells display dissimilar staining reactions that can be distinguished by use of different dyes.
What is the primary stain in gram staining? - crystal violet (purple)
what is the mordant in gram staining? - iodine
What does iodine do in gram staining? - combines with the crystal violet and forms an
insoluble complex in gram positive cells
