Final: Staining

Question 1

Is it possible to determine the species of a bacteria simply by looking at them under the microscope and determining their morphology and arrangement?

Answer 1

No because there are many types of bacteria that have the same shape and arrangement, and often times their arrangements do not hold up perfectly in nature.

Question 2

Describe the different bacterial arrangements

Answer 2

Coccus= occurring singularly
Diplococcus= in pairs
Streptococcus= in chains
Staphylococcus= in clusters
Tetrad; cube= clusters of 4; clusters of 8
Bacillus= occurring singularly (looks more like pills)

Question 3

What is heat-fixation and what does it accomplish? (Three things)

Answer 3

Heat-fixing kills the bacteria, makes them adhere to the slide, and coagulates cytoplasmic proteins to make them more visible

Question 4

Why must the slide be completely dry before heat-fixing?

Answer 4

If any liquid remains on the slide it will transfer excessive heat during heat-fixation and distort the bacterial cells

Question 5

Which has thicker cell walls, gram-negative or gram-positive bacteria?

Answer 5

Gram-positives

Question 6

Do gram-positive or gram-negative bacteria have an outer membrane

Answer 6

Gram-negative

Question 7

What are the steps of the Gram stain?

Answer 7

Step 1: crystal violet is added to the slide to turn the bacteria purple
Step 2: iodine is added to make the crystal violet harden and adhere to the cell walls of the gram-positive bacteria
Step 3: 95% ethanol (alcohol) solution is added to dissolve the thin cell walls of the gram-negatives,releasing the crystal violet stain from them
Step 4: involves the application of a second stain which will recolor the colorless gram-negative bacteria making them pink.