Size, Shapes and Arrangements of

Bacteria

Microbiology

Bacterial Shapes

• cocci

• bacilli

• spiral

Coccus

Cocci (pl.) are spherical or oval bacteria having one of several distinct arrangements based on their planes of division.

Arrangements of Cocci

• division in one plane– diplococcus (pairs)– streptococcus (chains)

• division in two planes– tetrad (squares of four)

• division in three planes– sarcina (cubes of eight)

• random planes

Diplococcus

Streptococcus pneumoniae

Streptococcus

Streptococcus pyogenes

Tetrad

Micrococcus luteus

Sarcina

Sarcina Spp.

Random/Clusters

Staphylococcus aureus

Bacillus

Bacilli (pl.) are rod-shaped bacteria. Bacilli all divide in one plane producing a bacillus, streptobacillus, or coccobacillus arrangement.

Arrangment of Bacilli

• bacilli (single)

• diplobacilli (pairs, few)

• streptobacilli (chains)

• coccobacilli (oval)

Bacilli

Pseudomonas aeruginosa

Diplobacilli

Moraxella catarrhalis

Streptobacilli

Bacillus subtilis

Coccobacilli

Bortedella pertussis

Spiral

Spirals come in one of three forms: – vibrio (comma-shaped)– spirillum (thick, rigid spiral)– spirochete (thin, flexible spiral)

Vibrio

Vibrio cholerae

Spirillum

Spirillum volutans

Spirochete

Treponema pallidum Leptospira interrogans

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