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		Oxidase	Urease
fermenter	fast			Escherichia coli, Klebsiella, Enterobacter
	slow			Citrobacter, Serratia
non-fermenter		positive		Pseudomonas, Burkholderia
		negative	positive	Helicobacter pylori, Proteus mirabilis
		negative	negative	Campylobacter, Shigella, Salmonella, Yersinia

Cocci

• Neisseria
  • Neisseria meningitidis
  • Neisseria gonorrheae

Coccobacilli

• Haemophilus (S. aureus satellite colonies)
• Pasteurella
• Brucella
• Bordetella pertussis
• Francisella tularensis
• Legionella

Anaerobes

• Bacteroides
• Fusobacterium