Gram-negative bacteria

• Bacteria that have a thin peptidoglycan layer in the cell wall and therefore stain [pink or red] on Gram stain
• Outer membrane contains lipopolysaccharide (LPS, which consists of lipid A, core polysaccharide, and O antigen)

Organisms

• Bacilli
  • Lactose-fermenting
    • Fast fermenters
      • Escherichia coli
      • Klebsiella
      • Enterobacter
    • Slow fermenters
      • Citrobacter
      • Serratia
  • Non-lactose-fermenting
    • Oxidase-positive
      • Pseudomonas spp.
      • Burkholderia spp.
    • Oxidase-negative
      • Urease-positive
        • Helicobacter pylori
        • Proteus mirabilis
      • Urease-negative
        • Campylobacter
        • Shigella
        • Salmonella
        • Yersinia
• Cocci
  • Neisseria
    • N. meningitidis
    • N. gonorrheae
• Coccobacilli
  • Haemophilus (S. aureus satellite colonies)
  • Pasteurella
  • Brucella
  • Bordatella pertussis
  • Francisella tularensis
  • Legionella
• Anaerobes
  • Bacteroides