CLOSE
WEBSITE OF THE STATE OF SOUTH DAKOTA DEPARTMENT OF HEALTH
Doneen Hollingsworth, Secretary of Health

Bacillus anthracis — Key Characteristics

  • Large, box-car shaped, gram-positive rod in short or long chains.
  • Non-swelling, oval spores formed when grown on culture media. (Not usually seen in clinical specimens.)
  • Encapsulated rods may be seen in clinical specimens.
  • Ground-glass appearance of colonies.
  • Nonhemolytic on sheep blood agar.
  • Nonmotile.
  • No growth on MacConkey.
  • Catalase positive.
  • Susceptible to penicillin.
  • Lecithinase positive.

Identification pitfalls to avoid

Large, gram-positive bacilli that grow aerobically as nonhemolytic colonies on sheep blood agar should not be discarded as a contaminant, but should be worked up to rule out B. anthracis.

Look-a-likes

  • B. megaterium (lecithinase negative, motile)
  • B. thuringiensis (penicillin R, motile)
  • Paenibacillus macerans (weak lecithinase, motile)
Share via: