Classification of bacteria

Kingdom: Monera Division: Eubacteriophyta Class: Bacteria

What is bacteria? They are prokaryotic organisms:

(they Don’t have organized nucleus surrounded by nuclear membrane and the DNA found free in the cytoplasm).

organisms made up of just one cell.

capable of multiplying by themselves, as they have the power to divide , this is called ( binary fission).

some bacteria can cause diseases.

Common Shapes of Bacteria

SPIRILLUM

COCCUS BACILLUS

vibrio

Aggregation of coccus shape:

monococcus

Staphylococci

Aggregation of Bacillus shape monobacillus

Culture medium Is a mixture of various nutrients which

are suitable for the growth of microorganisms

At least 500 different types Solid or liquid Inoculated by loops, needles, pipettes,

and swabs

Based on the physical state Liquid medium:

Without agar. for the proliferation of bacteria.

Solid medium: 1.5-2.5% agar. for the isolation and identification of bacteria e.g., slant, Petri dishes.

Semisolid medium: 0.3-0.5% agar. for the observation of bacterial motility and

preservation of bacteria.

Types of media

Semisolid media

Liquid media

Where we can find and isolate Bacteria?

We can isolate bacteria from any source:

1. Air2. Water 3. Dust 4. Human body ex.“skin, mouth and

nails”5. Foods6. Any other sources

Bacterial growth on culture media

Bacterial growth in culture medium

Colony morphology

Shape of colony

Edge

Elevation

Staining of BacteriaBacterial cells are almost colorless and transparent

A staining technique is often applied to the cells to color them →

Their shape and size can be easily determined under the microscope.

Staining may be a simple stain ( use only one type of stain ex: methylene blue) or complex stain ( ex: Gram stain)

Smear Preparation:

Preparation and Fixation of Bacteria for Staining.

Objective: To kill the microorganism & fix them to the slide to prevent them from being washed out during the process of staining.

Smear preparation

Flame the loop and let it to cool.

Put the bacterial suspension on a clean slide.

Fix the bacterial suspension by flam (avoid overheating).

Gram Stain:

It is the most important differential stain used in bacteriology because:

it classified bacteria into two major groups:

a)Gram positive:

Appears violet after Gram’s stain

b) Gram negative:

Appears red after Gram’s stain

Procedure:

Crystal violet(30-60 sec)

↓wash with water

Iodine(2 min)

↓ wash with water

Alcohol(10 sec)

↓ wash with water

Safranin(1 min)

wash with water, dry and examine with oil lens

Gram Staining Procedure

Results:Shape: Cocci

Aggregation: irregular clusters

Colour: Violet

Gram’s reaction: Gram’s +ve

Gram positive Staphylococci

Results:

Shape: Bacilli

Aggregation: Single

Colour: red

Gram’s reaction: Gram’s –ve

Gram negative monobacilli