microbiology

Question 1

describe the 3 main shapes of bacteria

Answer 1

• cocci, spherical
• bacili, rod shaped
• spirillum, spiral shaped

Question 2

define obligate aerobe

Answer 2

Can only reproduce or metabolise in an oxygen-rich environment

Question 3

define obligate anaerobe

Answer 3

Are unable to reproduce or metabolise where there is oxygen present

Question 4

describe facultative anaerobe

Answer 4

Thrive in an oxygen-rich environment but are also able to respire
anaerobically

Question 4

what is the gram staining method?

Answer 4

1. Smear a glass slide with the bacterial sample and use heat to fix.
2. Stain with crystal violet which binds to peptidoglycan.
3. Treat with iodine to fix the stain to the peptidoglycan.
4. Decolourise with alcohol to remove unbound crystal violet stain.
5. Counter stain with safranin.

Question 5

gram positive bacteria

Answer 5

Thick peptidoglycan
(murein) cell wall
that retains crystal
violet stain and so
appears violet or
purple.

Question 6

gram negative bacteria

Answer 6

Lipopolysaccharide
layer that is washed
away with the alcohol along with any crystal violet stain.
Gram-negative cells
then stain pink or
red with safranin.

Question 6

whats the difference between total and viable count?

Answer 6

Total count – living
and dead cells
Viable count – living
cells only