bacterial morphology and gram stain

• gram stain information

  • always included
  • cell wall form - gram+ or gram-
  • shape - cocci, bacilli
  • formation - diplococci, clusters, pairs, chains
  • additional information
  • quantity of bacteria - ex: 10^4
  • other cells in sample - WBC, RBCs, casts, etc
• bacterial shapes - cocci

  • coccus/cocci: spherical
  • diplococci: cocci arranged in pairs
  • eg, Streptococcus pneumoniae, Neisseria gonorrhoeae
  • streptococci: cocci arranged in chains
  • eg, Streptococcus pyogenes, Streptococcus agalactiae
  • staphylococci: cocci that divide in multiple planes and form grape like clusters
  • eg, Staphylococcus aureus
• bacterial shapes - bacilli

  • bacilli: rod shaped
  • coccobacilli: oval and similar to a coccus
  • eg. Haemophilus influenzae
  • branching or filamentous: resembling strands of hair or spaghetti
  • eg, Norcardia spp
• bacterial shapes

  • vibrio: curved or comma shaped rod
  • eg, Vibrio cholerae
  • spirillum: a thick, rigid spiral
  • eg, Helicobacter pylori
  • spirochete: a thin, flexible spiral
  • eg, Treponema pallidum
  • pleomorphic: can take on various shapes
  • eg, Mycoplasma spp
• atypical microorganisms

  • do not stain in gram stain
  • lack of cell wall
  • Mycoplasma spp
  • Ureaplasma spp
  • intracellular pathogens
  • Chlamydophila pneumoniae
  • Chlamydia trachomatis
  • Legionella spp.
• • qualitative: presence or absence of growth
  • semi-quantitative: grading of bacterial growth as rare (1 ), few (2+), moderate (3+), or heavy (4+) on selected media
  • number corresponds to quadrant
  • quantitative: actual colony count is provided