Lecture Notes: Bacterial Shapes and Arrangements

Introduction

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

Bacterial Shapes

1. Coccus (plural: Cocci)
   • Shape: Round or spherical cell
2. Bacillus (plural: Bacilli)
   • Shape: Rod-like
   • Usage: Can refer to a shape or as part of a bacterial name
3. Vibrio
   • Shape: Curved rod, comma-like
   • Example: Vibrio cholerae (causative agent of cholera)
4. Coccobacillus (plural: Coccobacilli)
   • Shape: Short rods, appear spherical
   • Examples:
     • Haemophilus influenzae (causes meningitis)
     • Bordetella pertussis (causes whooping cough)
5. Spirillum (plural: Spirilla)
   • Shape: Rigid spiral or corkscrew
   • Note: No significant clinical examples
6. Spirochete
   • Shape: Flexible corkscrew
   • Propulsion: Axial filament (unlike Spirillum's flagella)
   • Important examples:
     • Treponema pallidum (causative agent of syphilis)
     • Borrelia burgdorferi (causative agent of Lyme disease)

Key Differences

• Spirillum vs. Spirochete
  • Spirillum: Propelled by flagella, rigid
  • Spirochete: Propelled by axial filament, flexible

Bacterial Arrangements

1. Single
   • Single organism is either coccus or bacillus
2. Diplo
   • Diplo means two
   • Diplococcus: Pair of spheres
   • Diplobacillus: Pair of rods
   • Example: Streptococcus pneumoniae (often appears as diplococcus)
3. Tetrad
   • Group of 4
4. Sarcinae
   • Group of 8
5. Strepto
   • Means chain
   • Streptococcus: Chain of spheres
   • Streptobacillus: Chain of rods
6. Staphylo
   • Means cluster
   • Staphylococcus: Cluster of spheres
   • Note: No staphylobacillus because rods grow end to end, not side to side

Conclusion

• Key terms: Coccus, Bacillus, Vibrio, Coccobacillus, Spirillum, Spirochete
• Arrangements: Single, Diplo, Tetrad, Sarcinae, Strepto, Staphylo
• Remember: Bacterial shapes and arrangements help in identifying and classifying bacteria.

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• Have a wonderful day. Be blessed.