COLONY MORPHOLOGY ON AGAR PLATE CULTURES

Form of Colony

Elevation of Colony

Margin of Colony

Surface of Colony

MORPHOLOGY ON slant medium

•In a liquid medium, the region in which the organism grows depends on the oxygen

requirement of that particular species.

Liquid medium* Turbid

* Pellicle((thick growth at the top of the tube

* Sediment

There are

three common shapes of bacteria

1-Coccus

Diplococcus: a pair of cocci

having one of the following arrangements

Streptococcus: a chain of cocci

Tetrad: a square of 4 cocci

Sarcina: a cube of 8 cocci

Staphylococcus: cocci in irregular, often grape-like clusters

Bacillus (rod) 2-

Bacillus: a single bacillus

Streptobacillus: bacilli in chains

Coccobacillus: oval and similar to a coccus

Spiral 3-

Vibrio: an incomplete spiral or comma-shaped

Spirillum: a thick, rigid spiral

Spirochete: a thin, flexible spiral

Simple Stai

Simple Staining and Bacterial Cell Morphology

Preparing a smear for staining. (The following procedure is used for all of our staining)

•1. Flame (sterilize) your inoculating loop/needle before and after use .

2. Prepare the smear

a. If you have a solid culture (agar colony), place a small drop of water on a clean slide.

Drag the sterile inoculating needle tip through the edge of colony.

b. Gently spread the mixture into a circle.

A loop of liquid culture can be placed directly on the slide and spread out.

3. Let the smear air dry completely.

4. Heat-Fix the smear.

Smears are heat-fixed by quickly passing the slide through a flame two or three times.

This causes the microbes to stick to the slide and not get washed off during the staining process.

5. Stain the smear.

Place the slide on a rack over the sink. Flood the smear with stain and let it for 60-90 seconds. Rinse gently and blot dry.

6. Observe the slide under low and high-dry lenses to locate, center, and focus the image.

Then, place a drop of oil directly on the stained smear .Turn the oil lens into position and fine focus to observe the cells.

Coccus (cocci pl.)

Bacillus (Bacilli pl.)

Spirillum (Spirilli pl.)

Name the bacterial morphologies (shapes and arrangements) seen

here.

13

2

4

5

6Answers:

1 .Spirillum2 .Coccus3 .Bacillus4 .Diplobacillus5 .Streptobacillus6 .Diplococcus