Dr.Taghreed Khudhur Mohammad Lab.5 / 2015Ahmad Dawood Salman

Cultural characteristic

Bacteria grown artificially (in vitro) on agar plates are described as colonies vary in size, shape, pigment production and hemolysis on blood agar, depending on the type of media.

A. Description of colonies on solid culture

1- Shape: circular, irregular, radiating or rhizoid.

2- Surface: Bacterial colonies are frequently shiny and smooth in appearance. Other surface descriptions might be: veined عروق, rough, dull, wrinkled (or shriveled), glistening متأللئ.

3- Color – It is important to describe the color or pigment of the colony. Also include descriptive terms for any other relevant optical characteristics such as: opaque, cloudy, translucent, and iridescent متتقزح .

4- Size: Surface colonies are measured in millimeter, they are 2-3 mm in diameter. Smaller ones may be less than (about 0.5-1 mm).

5- Elevation: may be raised, low convex, implicated or dome shape

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6- Edges: mostly edges are entire, sometimes crenateمقرضة , fimbrated or effuse.

7- Color (pigmentation): some organism may produce pigmented colonies (Staphylococcus,Pseudomonas)

Staphylococcus on blood agar Pseudomonas

8- Opacity: colonies on nutrient agar may be transparent, translucent or opaque.

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9- Consistency : Mostly soft and butyrous and may be hard, firm, mucoid, tenacious, dry, adherent to medium, friable and membranous.

Klebsiella on blood agar and MacConkey agar

10- Contiguity: may be discrete or swarming.متصل نمو

Proteus on blood agar

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11- Changes in the medium: colonial growth may bring about color changes in the media themselves produce soluble pigment that diffuse in to the medium and some organism haemolysis the blood of medium around the colony.

Types of haemolysis are : a) Beta hemolysis is indicated by a clear colorless zone surrounding

the colonies. There has been total lysis of the red blood cells. e.g. Staphylococcus aureus

b) Alpha hemolysis is indicated by a small zone of greenish to brownish discoloration of the media. This is caused by the reduction of hemoglobin to methemoglobin. e.g. Streptococcus pneumoniae

c) Gamma hemolysis is indicated by no change in the media. E.g. Streptococcus faecalis

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12- Emulsifiability استحالب : Growth of some bacteria is easily emulsifiable (like E. coli, salmonella) whereas growth of N. catarrhalis is not emulsifiable and form granules.

13- Odor

Description of growth in liquid culture

Growth in liquid medium is described as:

1. Turbidity: Clear or turbid2. Deposit : Growth of Streptococcus pyogenous is characterized by deposit at

the bottom of the tube3. Surface growth: Surface growth is related to aerobic nature of organism.4. Color changes: Some organisms produce water soluble, pigment which

after diffusion change the color of medium e.g. Pseudomonas pyocyneous.

Quiz / 2Q1- How can you describe colonies on solid culture media ?

Preparing of bacterial smears5

Equipment:-1. Bacteriological Loop.2. Slide (clean and dry).3. Drop of water (If the culture medium is solid) 4. Bunsen burner 5. Bacteria

A//Making of dry smears from liquid media :

a. Sterilize loop in Bunsen flame.

2. 2.Using aseptic precautions االحتياطات, with draw one

loop full of culture.

3. 3.Transfer drop of culture to a clean slide

4. spread it with the loop to form a thick film of liquid.

5. Sterilize the loop.

6. Allow the film to dry without heating

7. Pass the slide 3 times through the Bunsen film flame.

8.Allow the slide to cool, and then stain the film .

B//Making of dry smears from solid media:

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Aseptic precautions must be observed during the manipulation of culture tubes or

plates.

1. Place one drop of distilled water on a clean slide by sterilized loop

2. Sterilized loop.

3. With the loop transfer to the slide a small portion of the growth to be

examined and Emulsify it in the drop of water until a thin

homogenous film is produced.

4. Sterilize loop in Bunsen flame

5. Allow the smear to dry ( air )

6. Fix by rapidly pass the slide 3 times through the Bunsen film

flame.

Advantages of Fixation1- kills organisms(Organism dies) [usually results in the death of the

attached microorganisms]2- adheres specimen strongly to the glass slide3- promotes stain ability of specimen

Quiz1

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Fill in the blanks with suitable answer :-

1. The advantage of preparing wet smears is to observe_________.

2. Preparing dry smears is to observe__________.3. There are two types of fixing bacterial smear

___________and_________.

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