Prokaryotic Classification and Differential Staining

Characteristic signs of staphylococci:

• gram-negative cocci

• gram-positive cocci

• motionless bacteria

• strict anaerobes

• facultative anaerobes

Escherichia coli

• positive

• negative

Streptococcus sp

• positive

• negative

Staphylococcus sp

• positive

• negative

Which organism cannot survive in the presence of oxygen?

• heterotrophs
• autotrophs
• obligate anaerobe
• facultative anaerobe

The staining procedure that uses at least two different colors of stains or dyes:

• Simple stain

• Differential stain

• Negative Stain

• Acid-fast stain

What is the purpose for heat fixing a slide?

• Kills the bacteria and helps it adhere to the slide

• Bursts the cell walls which allows the stains to penetrate

• Makes bacterial cells gram variable

• Causes the bacteria to lose their natural color

How are gram positive and gram negative bacteria distinguished from each other?

• Gram (+) bacteria are pathogens and gram (-) are not

• Gram (-) bacteria are distinguished by their smaller size

• Gram (+) and gram (-) bacteria are distinguished by their capsule type

• Gram (+) and gram (-) are distinguished by their cell walls

What is the first step in gram staining a heat-fixed smear?

• Apply the mordant (iodine)

• Apply the primary stain (crystal violet)

• Counterstain using safranin

• Decolorize with the acetone-alcohol decolorizer

What is the purpose of the mordant>

• The mordant is iodine which kills bacteria

• The mordant decolorizes bacteria

• The crystal violet/iodine complex stains the cells pink

• Combines with the primary dye and helps stabilize it within the peptidoglycan