how does smear preparations of cells from a liquid medium differ from preparation of cells from a solid medium?
cells from a solid medium are placed in a drop of liquid on the slide then smeared. this is not necessary for a loop of cells from a liquid culture
why is it important to limit the quantity of cells used to prepare a smear?
if too many cells are used to create a smear, it wil be difficult to distinguish individual cell shapes and arrangements from large clumps of cells. also staining and destaining techniques do not work well on clumped and layered cells in a smear
for preparation of a smear on a slide, what is the purpose of heat fixation? what problems can arise when the slide is heated on the flame?
heat fixation of smears kills the bacterial cells and causes them to adhere to the glass so that they do not get washed off during staining. overheating can damage and dehydrate the cells causing them to distort in shape. also the glass can crack or shatter
what causes a stain to adhere to bacterial cells? why are all colored dyes not necessarily useful for simple staining?
basic dyes, which carry a positive charge, will adhere to negatively charged cell surface structures. acidic dyes will not adhere because of the electrostatic repelling forces
which type of microscopy produces an image of unstained cells that is most similar to the one achieved by negative staining?
darkfield microscopy of unstained cells creates an image most similar to negative stainging
how might flourescence microscopy be used to visualize the bacterial capsule?
flourescent dyes linked to antibodies specific to the bacterial capsule can be used to tag and visualize the capsule by flourescence microscopy
why are encapsulated strains of strept. pneumoniae more likely to cause disease than strains that do not produce a capsule?
encapsulated strains of s. pneumoniae are protected against phagocytosis in the host and are more likely to cause infection than unencapsulated strains
a basic dye is utilized to stain bacterial cells:
a stain that does not penetrate cells is used to color the background:
useful for visualizing spirochaetes:
useful for visualing the glycocalyx of certain bacterial species:
cells are mixed with a stain before they are smeared on the slide:
heat fixation of the slide is not recommended:
water is used to remove excess stain from the slide:
for the simple stain procedure, one can use:
crystal violet and methylene blue
for the negative stain procedure, one can use
india ink and nigrosin
before heat fixation, a wet smear of bacterial cels on a slide must be:
bacterial capsules can consist of:
polysaccharides and polypeptides with unique amino acids