Laboratory Techniques

Question 1

what is studied when considering colonial morphology?

Answer 1

the shape, colour, texture and size of the colony

Question 2

what cell morphologies can be observed?

Answer 2

cocci (spherical)
rods
vinrio (comma-shaped)
spirilllum (spiral-shaped)

Question 3

what are the two fixation techniques and how do they differ?

Answer 3

heat fixation - gentle flame heating; preserves the overall morphology but not delicate cell structures
chemical fixation - chemicals penetrate cells to react with cellular components; preserves fine cell structure

Question 4

what are the main features of dyes?

Answer 4

dyes have chromophore groups (conjugated double bonds) that give the dye its colour
they bind to cell components (covalent, ionic, hydrophobic bonds)

Question 5

describe the staining technique developed by Paul Ehrlich

Answer 5

Paul Ehrlich developed the acid-fast staining technique, the action of which depends upon the high lipid content of cell walls.

1. smear and hot carbol fuchsin
2. wash with water
3. 10 min 20% H2SO4
4. wash with water
5. counterstain with methylene blue

Question 6

describe the staining technique developed by Christian Gram

Answer 6

Christian Gram developed the Gram stain, which distinguishes two classes of bacteria on the basis of their cell wall structure.

1. heat fixed smear + crystal blue
2. iodine/KI added to form CVI complex in the cell
3. wash with solvent eg. 90% ethanol
4. stop with water
5. counterstain with eg. carbol fuchsin

Question 7

what is the result of the acid-fast stain?

Answer 7

acid-fast bacteria appear bright red and are often in clumps

non-acid fast bacteria stain blue

Question 8

what is the result of the Gram stain?

Answer 8

Gram-positive bacteria appear dark purple

Gram-negative bacteria appear pink or red