bacterial morphology

• Morphology

  The study of form and structure
• Morphologic types of cocci

  • Diplococci - occur in pairs of cells
  • Streptococci - cells arranged in beads or chains
  • Staphylococci - irregular clusters resembling bunches of grapes
  • Tetrads - four cells arranged in a square along the same plane of division
  • Sarcinae - cuboidal arrangement of usually 8 or more cells along three dimensions
• Bacilli


  Cylindrical or rod-shaped bacteria
• Diplobacilli


  Bacilli occurring in pairs
• Streptobacilli


  Bacilli occurring in chains
• Corynebacteria


  Bacilli displaying a palisade arrangement, with cells lined side by side like matchsticks
• Most bacilli occur as single, unattached cells
• Divisions of spiral-shaped bacteria

  • Spirilla - actual spirals or helices, with relatively rigid cell bodies
  • Spirochetes - spiral bacteria able to flex and wriggle their bodies while moving
  • Vibrio/Comma Bacteria - short incomplete spirals
• Monomorphic


  Most bacteria are of this type
• Pleomorphic


  A few bacteria are of this type, exhibiting unusual shapes
• Approximate composition of the bacterial cell

  • Water - 70%
  • Dry Weight - 30%
  • Protein - 70%
  • RNA - 12%
  • DNA - 3%
  • Lipids - 6%
  • Polysaccharides - 5%
  • Phospholipids - 4%
• Flagella


  Thin, hairlike appendages protruding through the cell wall
• Classification of bacterial cells by flagella location and number

  • Monotrichous - with one polar flagellum
  • Amphitrichous - single flagellum at both ends
  • Lophotrichous - with tufts of flagella at both poles
  • Peritrichous - 8 or more flagella distributed over the surface
  • Atrichous - bacteria without flagella
• Functions of flagella

  • Motility
  • Antigenicity - the protein composition serves as the antigen and therefore elicits antibody specific for flagella
• Detection of flagella

  Motility test - directly observed by microscopic examination or indirectly observed by growth in semisolid medium
• Pili/Fimbriae

  Shorter and finer than flagella, seen in both motile and non-motile bacteria, not concerned with motility
• Types of pili

  • Ordinary pili - play a role in adherence of symbiotic bacteria to host cells
  • Sex pili - responsible for attachment of donor and recipient cells in conjugation
• Functions of fimbriae

  • Facilitate DNA transfer during bacterial conjugation
  • Serve as attachment site for bacterial viruses
  • Facilitate adherence to mammalian surfaces
  • Antigenicity
• Capsule


  A condensed, well-defined layer surrounding the cell made up of polysaccharide
• Slime layer


  Masses of polymer which appear detached from cells but entrap them, giving a mucoid or viscous colony
• Glycocalyx


  A loose meshwork of fibrils extending outward from the cell
• Chemical composition of capsules

  • Polysaccharide
  • Polypeptide
  • Nucleic acid admixed with polysaccharide
• Functions of capsules

  • Antiphagocytic and antibacteriophage
  • Antigenic
• Significance of capsules

  • Associated with virulence, making infections more difficult to combat due to antiphagocytic property
  • Capsular material can be extracted and used in preparation of dextran, cellulose and levans from sucrose
• Cell wall

  Lies between the capsule and the cytoplasmic membrane, rigid and elastic, retains original shape
• Peptidoglycan/murein


  A complex polymeric substance found in all bacterial cell walls, provides strength and rigidity
• Functions of cell wall

  • Protects cell from mechanical damage and osmotic rupture
  • Essential for bacterial growth and cell division
  • Responsible for cell shape
  • Major distinction between gram-positive and gram-negative bacteria
  • Antigenic specificities
• Protoplasts


  Formed after removal of cell wall from gram-positive bacteria
• Spheroplasts


  Formed after removal of cell wall from gram-negative bacteria
• Cytoplasmic membrane/Protoplasmic membrane


  Thin covering lying immediately beneath the cell wall, essential for viability
• Functions of cytoplasmic membrane

  • Selective permeability - controls passage of nutrients and waste
  • Contains enzymes for complex lipid synthesis, cell wall components, electron transport, and oxidative phosphorylation
• Mesosomes


  Extensions of the cytoplasmic membrane, associated with vital processes
• Functions of mesosomes

  • Involved in septum formation during cell division
  • Associated with bacterial nuclear material
  • Sites of respiratory enzymes, providing increased membrane surface
• Ribosomes


  RNA-protein particles containing enzymes for protein synthesis
• Nuclear material


  DNA confined to an area within the cytoplasm, carries messages controlling cell activities
• Cytoplasmic inclusions


  Concentrated deposits of certain substances, also known as volutin or metachromatic granules
• Endospores


  Thick-walled oval bodies produced by some bacteria, resistant to physical and chemical agents
• Sporulation


  The process of spore formation, representing a dormant phase of the bacterial cell
• Bacteria capable of producing endospores

  • Bacillus
  • Clostridium
  • Desulfotomaculum
  • Sporolactobacillus
  • Sporosarcinae
• Location of spores within the cell

  • Central
  • Terminal
  • Subterminal