9.3

• MAC - Negative

  • Pseudomonas
  • Burkholderia
  • Achromobacter
  • Chryseobacterium
  • Sphingobacterium
  • Alcaligenes
• Gram Negative Bacilli

  • Bordetella (NP)
  • Comamonas
  • Vibrio
  • Aeromonas
  • Plesiomonas
  • Chromobacterium
• The most frequently used primary selective and differential agar
• MAC contains crystal violet dye to inhibit the growth of gram-positive bacteria and fungi
• MAC allows many types of gram-negative bacilli to grow
• The pH indicator in MAC is neutral red
• Bacterial fermentation of lactose results in acid production
• Acid production causes the pH indicator to give bacterial colonies a pink to red color
• Cytochrome oxidase


  Participates in electron transport and in the nitrate metabolic pathways of certain bacteria
• 1% tetramethyl-p-phenylenediamine dihydrochloride is the reagent used for oxidase testing
• A sample of the bacterial colony can be rubbed onto filter paper impregnated with the reagent
• The oxidase test is initially used for differentiating between groups of gram-negative bacteria
• Oxidase – Positive


  • Pseudomonas paucimobilis
  • Sphingomonas paucimobilis
  • S. parapaucimobilis
• Sphingomonas paucimobilis has small, circular, smooth, convex; bright yellow growth pigment on BAP
• Moraxella characteristics

  • Don’t ferment CHO
  • DNAse (+)
  • Oxidase (+)
  • Catalase (-)
  • Coccobacilli
• M. catarrhalis is a coccus that morphologically resembles Neisseria spp.
• Normal flora of mucous membrane
• Moraxella is an opportunistic pathogen causing pneumonia and wound infections
• Moraxella is also known as Morax axenfield bacillus or haemophilus duplex
• Moraxella is isolated from patients with blepharoconjunctivitis
• Moraxella fails to grow on McConkey
• Moraxella produces pitting of blood agar
• Bacterial Blepharoconjunctivitis is commonly caused by M. lacunata and S. aureus
• Other Moraxella species

  • Moraxella osloensis
  • Moraxella urethralis
• Moraxella urethralis is now named Oligella urethralis
• Eikenella characteristics

  • Small, even straight sided
  • Capnophilic
  • Facultative anaerobic
  • Oxidase, LDC, nitrate (+)
• Eikenella is normal flora of mouth & GIT
• Eikenella is a common etiologic agent of human bite and clenched fist wounds
• Eikenella requires blood for growth
• Growth of Eikenella is enhanced by the presence of hemin (X factor) in the medium
• Chocolate agar is the best supportive medium for Eikenella
• Eikenella shows growth on blood or chocolate agar but not on MacConkey’s agar
• Eikenella has a bleachlike odor
• Pasteurella characteristics

  • Parasites of wild animals and birds
  • Agent of shipping fever in cattle
  • Hemorrhagic septicemia
  • P. multocida is the most important human pathogen
  • Wound infection (animal bite/scratches) is the most common type of Pasteurella infection
• Virulent Pasteurella organisms produce a capsule
• Pasteurella does not grow on McConkey
• Pasteurella lab findings

  • Gram-negative bacillus
  • Grows on blood agar only
  • Oxidase and indole positive
  • ONPG negative
• Pasteurella BAP colonies show brownish discoloration of medium emitting a musty/mushroom-like odor
• Actinobacillus characteristics

  • Normal oral flora of animals
  • Rarely associated with human infection
  • Transmitted by bite wounds or contamination of preexisting wounds during exposure to animals
• Actinobacillus may be found in animal bite wounds