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 BACILLUS COCCUS vibrio SPIRILLUM

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

Types of media Semisolid medium: 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.

Semisolid media Liquid media

Where we can find and isolate Bacteria? We can isolate bacteria from any source: Air Water Dust Human body ex.“skin, mouth and nails” Foods Any other sources

Bacterial growth on culture media

Bacterial growth in culture medium

Colony morphology Shape of colony Edge Elevation

Staining of Bacteria Bacterial 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)

Preparation and Fixation of Bacteria for Staining. 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).

Appears violet after Gram’s stain Gram Stain: It is the most important differential stain used in bacteriology because: it classified bacteria into two major groups: Gram positive: Appears violet after Gram’s stain b) Gram negative: Appears red after Gram’s stain

wash with water, dry and examine with oil lens Procedure: Crystal violet (30-60 sec) ↓wash with water Iodine (2 min) ↓ wash with water Alcohol (10 sec) Safranin (1 min) wash with water, dry and examine with oil lens

Gram Staining Procedure

Results: Gram positive Staphylococci Shape: Cocci Aggregation: irregular clusters Colour: Violet Gram’s reaction: Gram’s +ve Gram positive Staphylococci

Results: Gram negative monobacilli Shape: Bacilli Aggregation: Single Colour: red Gram’s reaction: Gram’s –ve Gram negative monobacilli

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