SHAPE AND ARRANGEMENT OF BACTERIA

 SHAPE AND ARRANGEMENT OF BACTERIA

Shape and Arrangement of Bacteria (Source: microbiologyinfo.com)

            The basic bacterial shapes are (a) Coccus (spherical), (b) Bacillus (rod-shaped), and (c) Spiral (twisted), (d) Filamentous bacteria, (e) Box shaped bacteria, (f) Appentaged bacteria and (g) Pleomorphic bacteria can assume several shapes.

a) SPHERICAL BACTERIA (COCCUS)

·       Cocci (or Coccus for a single cell) are round cells which are spherical or ovoid in shape, sometimes slightly flattened when they are adjacent to one another (plural - Cocci).

Arrangement of Coccus

i.     Diplococcus – Cocci arranged in pairs (Streptococcus pneumoniae, Moraxella catarrhalis, Enterococcus sp. and Neisseria gonorrhea)

ii. Streptococcus – Cocci arranged in form of chains (string like) (Streptococcus pyogenes and Streptococcus mutans).

iii.   Tetrads – Cocci arranged in packets of four cells, as the cell divides in two plains (Pediococcus sp. and Tetragenococcus sp.).

iv.   Sarcinae - Cocci arranged in packets of eight cells (cuboids), as the cell divides in three plains (Sarcina aurantiaca, Sarcina ureae, Sarcina lutea and Sarcina ventriculi).

v. Staphylococcus – Cocci arranged in form of Grape like clusters (Staphylococcus aureus and all Coagulase negative Staphylococcus sp.).

b) ROD SHAPED BACTERIA (BACILLUS)

·       The cylindrical or rod-shaped bacteria are called ‘Bacillus’ (plural: Bacilli).

Arrangement of Bacillus

i.       Diplobacilli – Bacilli arranged in pairs (Coxiella burnetii, Moraxella bovis and Klebsiella rhinoscleromatis)

ii.     Streptobacilli – Bacilli arranged in chains (Streptobacillus lavaditi, Streptobacillus moniliformis, Streptobacillus felis and Streptobacillus hongkongensis)

iii.   Trichomes - Bacilli arranged in chains with larger area of end-to-end contact between the cells (Cyanobacteria).

iv.   Palisades - The bacilli bend at the points of division following the cell divisions, resulting in a palisade arrangement resembling a picket fence and angular patterns that look like Chinese letters (Corynebacterium diptheriae).

v.     Coccobacilli - These are so short and stumpy that they appear ovoid. They look like coccus and bacillus (Haemophilus influenzae, Gardnerella vaginalis, and Chlamydia trachomatis).

vi.   Vibrios - They are comma-shaped bacteria with less than one complete turn or twist in the cell (Vibrio cholerae, Vibrio parahaemolyticus and Vibrio mytili).

c) SPIRAL BACTERIA

·       The Spiral bacteria are rod-shaped bacteria, which have more than one twist in the cell.

·       Spiral bacteria usually occur singly.

·       There are two types of Spiral bacteria. They are

i.       Spirillum - They have rigid spiral structure. Spirillum with many turns can superficially resemble spirochetes. They do not have outer sheath and endoflagella, but have typical bacterial flagella (Campylobacter jejuni, Helicobacter pylori and Spirillum winogradskyi).

ii.     Spirochetes - They are flexible and can twist and contort their shape. They have outer sheath and endoflagella, but lack typical bacterial flagella (Leptospira interrogans, Treponema pallidum and Borrelia recurrentis).

d) FILAMENTOUS BACTERIA

·       Filamentous bacteria are very long thin filament-shaped bacteria.

·       Some of them form branching filaments resulting in a network of filaments called ‘mycelium’.

·       Example for Filamentous bacteria is Candidatus savagella.

e) BOX (OR) SQUARE (OR) RECTANGULAR SHAPED BACTERIA

·    Box shaped bacteria are flat, box-shaped bacteria with perfectly straight edges and sharp 90° angles at the corners.

·    Smaller cells are usually perfectly squares (2 × 2 µ), while larger cells are rectangular; about twice as long as they are wide (4 × 2 µ).

·   Example for Rectangular shaped bacteria is Haloarcula vallismortis and Haloarcula marismortui.

f) APPENTAGED BACTERIA

·       Appentaged bacteria possess extension of their cells, as long tubes in the form of stalk or hypha, or as buds.

g) STAR SHAPED BACTERIA

·       Star shaped bacteria are the bacteria that look like stars.

·       Example for Star shaped bacteria is Stella humosa.

h) PLEOMORPHIC BACTERIA

·       Pleomorphic bacteria do not have any characteristic shape unlike all others described above.

·       Pleomorphic bacteria can change their shape. In pure cultures, they can be observed to have different shapes.

Example for Pleomorphic bacteria are Mycoplasma pneumoniae and Mycoplasma genitalium.