Bacteria are classified based on their morphology (shape), arrangement, staining properties, and other characteristics.
Here are the main types of morphological classification:
Shape:
I. Cocci: Spherical bacteria.
Diplococci: Pairs of cocci (e.g., Neisseria).
Streptococci: Chains of cocci (e.g., Streptococcus).
Staphylococci: Clusters of cocci (e.g., Staphylococcus).
Tetrads: Groups of four cocci (e.g., Micrococcus).
Sarcinae: Cubic configuration of eight cocci.
II. Bacilli: Rod-shaped bacteria.
Diplobacilli: Pairs of bacilli.
Streptobacilli: Chains of bacilli.
Coccobacilli: Oval and similar to cocci.
III. Spirilla: Spiral-shaped bacteria with rigid bodies.
IV. Spirochetes: Spiral-shaped bacteria with flexible bodies.
V. Vibrios: Comma-shaped bacteria (curved rods).
Arrangement:
The arrangement of cells can give clues about their classification and identification. Examples include:
Singular: Individual cells separated from each other.
Pairs: Cells attached in pairs.
Chains: Cells arranged in chains.
Clusters: Cells grouped together in clusters.
Staining Properties:
A) Gram Stain:
Differentiates bacteria into Gram-positive (purple) and Gram-negative (pink) based on cell wall composition.
B) Acid-fast Stain:
Identifies acid-fast bacteria (e.g., Mycobacterium) that have waxy cell walls resistant to Gram staining.
C) Endospore Stain:
Highlights the presence of endospores in some bacteria.
Other Morphological Features:
A. Size: Varies significantly between species.
B. Motility: Presence and arrangement of flagella (monotrichous, lophotrichous, amphitrichous, peritrichous).
C. Colony Morphology: Appearance of bacterial colonies on agar plates, including size, shape, color, texture, and hemolysis on blood agar.