lab 7: negative stains. simple and capsule

acid dye

dye whose chromophore is an anion; the negatively charged chromophore is what makes the dye acidic

negative stain

staining around the subject of interest rather than staining the subject itself

capsule

glycoprotein shell around the bacterial cell; a type of glycocalyx and a virulence factor

why negative stains preserve cell shape and size better than positive stains

negative staining does not involve dehydrating agents, which helps prevent shrinking and distortion of cells

number of slides used for a simple nigrosin negative stain

2 slides are used: one slide holds the specimen and dye, and the second slide is used as the spreading slide

Klebsiella colony appearance

shiny, moist, smooth, and circular

Bacillus colony appearance

dull, dry, wrinkled, and irregular

which bacterium in the colony comparison has a capsule

Klebsiella

size of well-isolated colonies compared with less-isolated colonies

well-isolated colonies are usually larger because there is less competition and more nutrients available, allowing faster cell division

how capsules help bacteria resist dehydration

the capsule helps protect the bacterial cell from drying out

how capsules help bacterial adhesion

capsules help bacterial cells attach or adhere to surfaces

how capsules contribute to virulence

capsules can resist dehydration, promote adhesion, and interfere with the immune system

how capsules interfere with the immune system

capsules can provide antigenic camouflage and make it harder for white blood cells to attach to or interact with the bacterial cell

primary dye in the capsule stain

Congo red

type of dye used as the primary dye in the capsule stain

Congo red is an acid dye

what Congo red stains in the capsule stain

Congo red stains the background

counterstain in the capsule stain

Maneval's stain

type of dye used as the counterstain in the capsule stain

Maneval's stain is a basic dye

what Maneval's stain colors in the capsule stain

Maneval's stain stains the bacterial cell wall

why the capsule stain is a negative stain

the subject of interest, the capsule, is not stained

why the capsule stain is a differential stain

it uses multiple dyes and distinguishes the unstained capsule from the stained bacterial cell and background

appearance of the capsule in a capsule stain

the capsule remains unstained and appears as a clear or pale area surrounding the stained cell