Morphological Classification Of Bacteria (Best) Full Read

Morphological Classification Of Bacteria (10)

On the basis of shape, bacteria are classified as follows .

  1. Cocci: Cocci are small, spherical or oval cells. In Greek ‘kokkos’ means ‘berry’. In Greek ‘ko e.g. Micrococcus.

  2. Bacilli: It is derived from the Greek word ‘Bacillum‘ meaning ‘stick’. There are rod shaped cells. e.g. Bacillus anthracis. In some of the bacilli the length of the cells may be equal to width. Such bacillary forms are known as coccobacilli e.g. Bracella.

  3. Vibrios: They are comma shaped, curved rods e.g. Vibrio comma.
  4. Spirilla: These are longer rigid rods with several curves or coils. They have a helical shape and rapid bodies e.g. Spirillum ruprem.
  5. Spirochetes: They are slender and flexuous spiral forms.
  6. Actinomycetes: They are branching filamentous bacteria. The characteristic shape is due to the presence of a rigid cell wall e.g. Streptomyces species.
  7. Mycoplasmas: They are cell wall deficient bacteria and hence do not possess a stable morphology. They occur as round or oval bodies with interlacing filaments.
Morphological Classification Of Bacteria


Many times, cell wall synthesis becomes defective either spontaneously or as a result of drugs like penicillin, bacteria lose their distinctive shape. Such microorganisms are called protoplasts, spheroplasts or L forms.

The most common method of reproduction among bacteria is asexual binary fission. In his process, each cell splits by forming two new cells. Cocci appear in several characteristic arrangements or groupings.

  1. Diplococci: Cocci that split along one plane only, tend to arrange themselves in pairs e.g. Diplococcus pneumoniae.
  2. Streptococci: These cells divide in one plane and remain attached, to form chains. e.g. Streptococcus lactis.
  3. Tetracocci: Tetracocci divide in two planes and live in groups of four e.g.Gaffyka tetragena.
  4. Staphylococci: Cocci cells divide in three planes in an irregular pattern. These cells he ent produce bunches of cocci as in grapes e.g. Staphylococcus aureus.
  5. Sarcinae: Sarcinae cells divide in three planes in a regular pattern. These cells produce a cuboidal arrangement of group of a eight cells.
Morphological Classification Of Bacteria


Bacilli split only across their short axis. Arrangements of groupings formed by bacilli species are limited . They may appear as pairs (diplobacilli) e.g. Klebisella pneumoniae.

But some species are found in chains (streptobacilli) e.g. Bacillus subtilis. Beggiatoa and Saprospira species forms trichomes, which are similar to chains but have a much large area of contact between the adjacent cells .

The bacilli remain attached to each other at various angles by incomplete separation of the daughter cells, resembling the letters ‘V’ or ‘L’. This is called Chinese letter arrangements e.g. Corynebacterium diphtheriae.


Morphological Classification Of Bacteria

Microorganisms are classified as Bacteria , Rickettsiae , Actinomycetes , Fungi , Protozoa , Algae , Viruses )

History of Microbiology

Branches Scope & Importance of Microbiology

Classification of Microorganisms






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