Bacterial morphology

• Bacteria


  Metabolically active unicellular organisms that have cell walls but lack organelles and an organized nucleus, which divide by binary fission
• Bacteria contribute to disease pathogenesis
• Bacterial size


  • Spheres measurement usually ranges from about 2 um in diameter to 10.0 um-long spiral-shaped bacteria, to even longer filamentous bacteria
  • Average coccus is about 1 um in diameter
  • Average bacillus is about 1 um wide - 3 um long
  • Bacteria range in size from 0.2 to 5 micrometers
  • Mycoplasma, the smallest microbe, is comparable in size to poxviruses largest viruses and may survive without a host
  • The longest bacterium rods are 7 um in size, similar to yeasts and human red blood cells
• Bacterial reproduction


  1. Binary fission - bacteria divide; one cell splits in half to become two daughter cells

  2. The time it takes for one bacterial cell to split into two cells is referred to as that organism's generation time
• Bacterial basic shapes


  • Spherical (cocci)
  • Rod-shaped (bacilli)
  • Spiral (spirilla)
• Rod-shaped (bacilli)


  • Cylindrical, often mistaken as cocci
• Spiral-shaped (spirilli/spirilla)


  • Can be gently curved or corkscrew like, Rigid and capable of movement
• Morphologic arrangements


  Following binary fission, the daughter cells either completely separate or remain connected, resulting in a variety of morphologic arrangements
• Varieties of cocci


  • Diplococci
  • Streptococci
  • Staphylococci
  • Tetrad
  • Sarcina/Octad
• Diplococci


  Cocci that divide and remain attached in pairs
• Streptococci


  Rods that remain attached in chains after cell division
• Streptococci


  • Streptococcus pyogenes
  • Streptococcus pneumoniae
  • Streptococcus mutans
• Staphylococci


  Cocci in a grapelike cluster or broad sheet
• Tetrad


  A group of four cocci
• Tetrad


  • Aerococcus
  • Pediococcus
  • Tetragenococcus
• Sarcina/Octad


  A group of eight bacteria that remain in a packet after dividing
• Sarcina/Octad


  • Sarcina aurantiaca
  • Sarcina butschlii
  • Sarcina ventriculi
• Varieties of bacilli


  • Coccobacilli
  • Diplobacilli
  • Streptobacilli
  • Palisade
• Coccobacilli


  A bacterium that is an oval rod
• Coccobacilli


  • Chlamydia trachomatis
  • Haemophilus influenzae
  • Gardnerella vaginalis
• Diplobacilli


  Rods that divide and remain attached in pairs
• Diplobacilli


  • Coxiella burnetii
  • Klebsiella rhinoscleromatis
  • Moraxella bovis
• Streptobacilli


  Rods that remain attached in chains after cell division
• Palisade


  Picket fence-like shape due to a bend at the site of division during cell division; bacilli stack up next to each other, side by side
• Palisade


  • Corynebacterium diphtheriae
• Varieties of Spirilum


  • Vibrio (short curved rod and comma shaped with less than one turn or twist in cell)
  • Spirochetes (helical shape, flexible, have an axial filament which helps in motility)
  • Spirilla (Helical- shaped/Corkscrew form, similar structure to spirochete but more rigid)
• Spirochetes


  • Leptospira species (Leptospira interrogans)
  • Treponema pallidum
  • Borrelia recurrenti
• Spirilla


  • Campylobacter jejum
  • Helicobacter pylori
  • Spirillum winogradsky
• Spirochetes


  • Flexible & have an axial filament which helps in motility
  • The filaments travel the length of the bacterium, aiding in the twisting of the bacteria's motility
• Spirilla


  • Have a similar structure with spirochete but more rigid
  • Like spirochetes, have a flagellum, but they lack the endoflagella
• Other Shapes and Arrangements

  • Appendaged Bacteria
  • Pleomorphic Bacteria
  • Filamentous Bacteria
  • Club-shaped Rod Bacteria
  • Box-shaped Rectangular Bacteria
  • Triangular shaped Bacteria
  • Stalked Bacteria
  • Star-shaped Bacteria
• Appendaged Bacteria


  • Bacteria that produce a distinct structure such as pillus or fimbriae
  • Those that produce these appendages are more virulent
• Appendaged Bacteria


  • Neisseria gonorrhea, the agent of Gonorrhea
• Pleomorphic Bacteria


  • Bacteria that do not have a defined form
  • They can alter shape, but in pure culture, they appear to have a definite form
• Pleomorphic Bacteria


  • Mycoplasma pneumonior, M. genitalium
• Filamentous Bacteria


  Filament-shaped bacteria that are long, thin, sometimes divide to form branches resembling strands of hair or spaghetti called mycelium
• Filamentous Bacteria


  • Actinomyce
• Club-shaped Rod Bacteria


  Bacteria that are thinner on one side than the other
• Club-shaped Rod Bacteria


  • Corynebacterium
• Box-shaped Rectangular Bacteria


  • Humaircula Marismorhi