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• 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
• Bacteria size

  • Spheres measurement usually ranges from about 0.2 um in diameter to 10 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 02 to 5 micrometers
• Bacterial morphology


  The study of the form and structure of bacteria
• Mycoplasma


  The smallest microbe, comparable in size to poxviruses (largest viruses) and may survive without a host
• Longest bacterium rods

  7 um in size, similar to yeasts and human red blood cells
• Bacterial reproduction

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

  2. Organism's Generation time - the time it takes for one bacterial cell to split into two cells
• Bacterial basic shapes

  • Spherical (cocci)
  • 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 arrangement varieties of cocci

  • Diplococci (cocci that divide and remain attached in pairs)
  • Streptococci (rods that remain attached in chains after cell division)
  • Staphylococci (cocci in a grapelike cluster or broad sheet)
  • Tetrad (a group of four cocci)
  • Sarcina/Ostad (a group of eight bacteria that remain in a packet after dividing)
• Varieties of bacilli

  • Coccobacilli (oval rod)
  • Diplobacilli (rods that divide and remain attached in pairs)
  • 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)
• Varieties of spirilla

  • Vibrio (short curved rod and comma shaped with less than one turn or twist in cell)
  • Spirochetes (have a helical shape, flexible & have an axial filament which helps in motility)
  • Spirilla (helical-shaped/corkscrew form, have a similar structure with spirochete but more rigid, like spirochetes have a flagellum but lack the endoflagella)
• Other shapes and arrangements

  • Appendaged bacteria (produce a distinct structure such as pillus or fimbriae, more virulent)
  • Pleomorphic bacteria (do not have a defined form, can alter shape but in pure culture appear to have a definite form)
  • Filamentous bacteria (filament-shaped, long and thin, sometimes divide to form branches resembling strands of hair or spaghetti called MYCELIUM)
  • Club-shaped rod bacteria (thinner on one side than the other)
  • Box-shaped/rectangular bacteria (nonpathogenic)
  • Triangular-shaped bacteria (live on saline environments such as salt lakes, marine salterns, and saline soils)
  • Stalked bacteria (possess a stalk on one end of the cell, found in lakes and streams)
  • Star-shaped bacteria (found in freshwater, soil, and sewage)
• Glycocalyx


  Thick layer of material outside the cell wall, outermost covering of some bacteria, gelatinous substance produced by the cell membrane and secreted outside the cell wall
• Capsule


  An outer, viscous and gelatinous covering on some bacteria composed of a polysaccharide or polypeptide, highly organized and firmly attached to the cell wall, serves as antiphagocytic infection, protects the encapsulated bacteria from being phagocytized by phagocytic WBC, indicative of virulence and degree of pathogenicity
• Slime layer


  Part of the glycocalyx that is unorganized and loosely attached to the cell wall, allows bacteria to slide or glide along solid surfaces, mediates adherence to surfaces
• Cell wall


  The outermost component of all bacteria (except Mycoplasma species), provides rigidity, strength, and protection, composed of peptidoglycan (also known as murein succulus)
• Gram-positive cell wall


  • Thick/multilayered, contains teichoic acids (for attachment and antigenic, crucial in cell shape determination, cell division regulation and other aspects) and polysaccharides (carbohydrates consisting of many sugar units)
• Gram-negative cell wall


  • Thin monolayered, has an outer membrane located outside of the peptidoglycan layers, contains lipoprotein (responsible for endotoxin production) made up of O-antigen, core polysaccharides, and lipid A, has a periplasmic space (fluid filled space between outer membrane and cytoplasmic membrane)
• Cell membrane/cytoplasmic membrane


  Located beneath the cell wall, encloses the cytoplasm of the cell, selectively permeable
• Cell structures - projecting structures

  • Pili or fimbriae (appendages used for attachment, thinner than flagella, not associated with actual motility)
  • Flagellum (whip-like structure for motility, enables cell to swim through liquid environments, types include monotrichous, lophotrichous, amphitrichous, peritrichous, atrichous)
  • Axial filament (two flagella-like fibril structure for motility found in spirochetes, allows them to move in a spiral, helical, or inchworm manner)
• Cell structures - internal structures

  • Nucleoid (region containing the chromosome)
  • Mesosomes (extensions of the cell membrane present in cytoplasm, serve in DNA replication and guide distribution of duplicated bacterial chromosomes)
  • Ribosomes (tiny spherical organelles that make proteins, target site of some antibiotics)
  • Granules or inclusion bodies (storage vessels, e.g. glycogen)
  • Endospores (resting structures formed inside some bacteria, allow survival in extreme conditions)
  • Cytoplasm (gelatinous nutrient matrix where organelles are suspended)
• Culture media types

  • Liquid media (broth, milk, infusion - does not solidify)
  • Semi-solid media (clot-like consistency, solidifying agent like gelatin/agar - thickens but not firm)
  • Solid media (firm surface, can be liquefiable and non-liquefiable)
• Culture media functions

  • General purpose media (to grow and support broad spectrum of microbes)
  • Enrichment media (for selected/desired microorganisms, uses blood, serum, or growth factors)
  • Selective media (used to grow a "selected" microorganism, prevents other organisms from growing)
  • Differential media (allows for growth of several types of microorganisms to show differences)