The shape of bacteria (Coccus, Bacillus, Spirochete, Actinomycetes)

Shape of bacteria

Depending on their shape, bacteria are classified into several types.

1. Cocci: The cocci (kokkos, berry) are oval or spherical cells. These may be arranged in pairs (e.g., pneumococci, meningococci, and gonococci), tetrads (micrococci), chains (e.g., streptococci), and clusters (e.g., staphylococci).

2. Bacilli: The bacilli (bacillus, rod) are rod shaped. These bacilli may show either of the following arrangement:

(a) Coccobacilli: The length of the bacteria is approximately the same as its width, e.g., Brucella.

(b) Streptobacilli: These are arranged in chains, e.g., Streptobacillus.

(c) Comma shaped: They exhibit curved appearance, e.g., Vibrio.

(d) Spirilla: They exhibit rigid spiral forms, e.g., Spirillum.

3. Spirochetes: Spirochetes (spira, coil; chaite, hair) are slender, flexuous spiral forms, e.g., Treponema.

4. Actinomycetes: Actinomycetes (actin, ray; mykes, fungus) are branching filamentous bacteria resembling fungi. They possess a rigid cell wall.