Microbio Lab Bacterial Cell morphology and staining

irregular arrangements of cocci bacteria

bacilli that resemble cocci

• long multinucleate
• filaments or hyphae that may
• branch to produce a network

• variable in shape and
• lack a single, characteristic form

to affix bacteria to slide

• In this staining method we use a single stain or dye to
• create contrast between the bacteria and the background

• ¤These stains/dyes
• include:

Crystal Violet

Carbolfuchsin

• Methylene
• blue

• ¨When a specific specimen doesn’t stain well, the use of
• negative staining can be utilized to observe the overall morphology of the
• cells

¨Do not Heat Fix

• ¨Negative/indirect/background staining can be
• achieved using an acidic stain, such as:

¤Nigrosin

• ¤India
• Ink

¤Eosin

• ¨These stain’s will not penetrate the cell because the
• stain’s have an overall (-) charge as do the cells

• ¨Divides bacteria into two different groups based on the
• gram staining properties of the cell wall

¤Gram Positive

¤Gram Negative

• ¨This is carried out by first staining with the primary
• stain, which in
• this case is crystal violet (purple). this is to stain the gram positive bacteria 

¨This is followed by the mordant, iodine

• ¤A mordant increase
• the interaction between the stain and the bacterial cell

• ¨Excess/unbound stain is washed off with decolorizing
• agent such as 95% ethanol or isopropanol-acetone

• ¨The smear is the counter-stained with safranin
• (pink). This is to stain the gram negative bacteria.

• ¤A mordant increase
• the interaction between the stain and the bacterial cell

• ¨Acid Fast refers to the physical property of a bacteria
• of which has a high myolic acid content in its cell wall

• ¤Once stained, can not
• be easily decolorized by acids.

• ¤Nor do they stain
• easily with simple stains such as gram’s staining

you place a few drops of carbolfuchsin on the microorganism on the slide and heat the slide with the carbolfuchsin still on the slide. then you rinse the slide with water, decolorize with ethyl alcohol, rinse again with water, add methylene blue.

apply malachite green to the slide while allowing the slide to heat up by using hot steam. counterstain with sarfranin

no, only some

• it is a slimy layer on the outside of a bacterium. it's composition varies for different bacteria. Polysaccharides, polypeptides, and glycoproteins have all been found in
• capsules

capsules allow bacteria to evade phagocytic cells.

flood the slide with crystal violet. rinse thoroughly with copper sulfate.