Lecture Notes: Bacterial Shapes and Arrangements

Introduction

• Presenter: Dr. O
• Topic: Common bacterial shapes and arrangements.

Bacterial Shapes

1. Coccus

• Definition: Spherical or round cells.
• Plural Form: Cocci.

2. Bacillus

• Definition: Rod-shaped cells.
• Usage: Can be a name or a shape descriptor.
  • Example: "Bacillus" (capitalized) refers to the name of an organism and indicates rod shape.

3. Vibrio

• Definition: Curved rod, comma-shaped.
• Key Example: Vibrio cholerae, causative agent of cholera.

4. Coccobacillus

• Definition: Short rods resembling spheres.
• Examples:
  • Haemophilus influenzae (can cause meningitis)
  • Bordetella pertussis (can cause whooping cough)

5. Spirillum

• Definition: Rigid, large spiral or corkscrew-shaped organisms.
• Note: No important clinical examples.

6. Spirochetes

• Definition: Corkscrew-shaped, more flexible than spirillum.
• Movement: Use axial filament.
• Key Examples:
  • Treponema pallidum (causative agent of syphilis)
  • Borrelia burgdorferi (causative agent of Lyme disease)

Differences Between Spirillum and Spirochetes

• Spirillum: Propelled by flagella on the ends.
• Spirochetes: Use axial filament for movement.

Bacterial Arrangements

Basic Arrangements

• Single: Coccus or bacillus

Diplococcus/Diplobacillus

• Meaning: Pair of spheres (diplococcus) or rods (diplobacillus).
• Important Example: Streptococcus pneumoniae (usually found as diplococcus).

Tetrad

• Definition: Group of 4.

Sarcinae

• Definition: Group of 8.
• Note: Not significant in discussion.

Strepto and Staphylo

• Strepto: Means chain (used for chains of cocci or bacilli).
• Staphylo: Means cluster (only used for cocci, not bacilli).

Important Notes

• No Staphylobacillus: Rods grow end to end, not side to side, hence no cluster formation.
• Clarification: Streptococcus and Staphylococcus exist, but no Staphylobacillus.

Conclusion

• Key Terms Covered: Coccus, Bacillus, Vibrio, Coccobacillus, Spirillum, Spirochete, Strepto, Staphylo.
• Final Words: Have a wonderful day and be blessed.