BIOL 2401 Lab Exam

When should the inoculating loop be flamed when streaking agar plates?

1. Before streaking the first 1/3

2. Before streaking second 1/3

3. After streaking the last 1/3

Supplies needed for catalase test

• Microscope slide

• Toothpick (to transfer isolated colonies)

• Hydrogen peroxide

Appearance of positive catalase test

Bubbles after adding hydrogen peroxide

Supplies needed for coagulase test

• Reaction card with two circles (one for control, one for test)

• Control reagent

• Test reagent

• Agar plate with cultures

Appearance of positive coagulase test

Clumping (agglutination)

Components of colony morphology (SSPMET)

Size, Shape, Pigmentation, Margin, Elevation, Texture

Examples of shape (colony morphology)

• Circular

• Irregular

• Rhizoid

• Punctiform

Examples of margin (colony morphology)

• Filamentous

• Lobate

• Undulate

• Serrate

• Entire

Examples of elevation (colony morphology)

• Raised

• Convex

• Flat

• Umbonate

• Crateriform

When should a slide be heat-fixed (gram staining)?

After the bacterial smear has air-dried and before adding any gram stain reagents

Steps of gram staining (CIDS)

1. Crystal violet → 60s → rinse

2. Iodine → 60s → rinse

3. Decolorizer drop-by-drop → rinse

4. Safranin → 60s → rinse, gently blot or air dry

Components of cell morphology (GCC)

Gram reaction, cell shape, cell size

Examples of cell shape (cell morphology)

• Coccus

• Coccobacillus

• Bacillus

• Vibrio

• Spirillum

• Spirochete

Steps to adjust microscope for Köhler Illumination (set up at 40x)

1. Close aperture diaphragm (limits light)

2. Close field diaphragm (makes hexagon)

3. Raise condenser fully, adjust (makes sharp hexagon)

4. Adjust screw (centers hexagon)

5. Open field diaphragm

6. Open aperture diaphragm

Steps to prepare a slide before gram staining

1, Sterilize loop

2. Add loopful of water to slide

2. Sterilize loop

3. Smear part of isolated colony on slide

4. Let fully air dry

5. Heat fix

Positive mannitol fermentation result

Red agar turns yellow

Beta hemolysis

Complete hemolysis → turns clear

Alpha hemolysis

Partial hemolysis → turns green

Gamma hemolysis

No hemolysis → stays red