Francisella tularensis — Colony characteristics
F. tularensis is highly infectious! Once this organism is suspected on the basis of clinical and/or laboratory information, do not perform additional testing. Send the isolate to the South Dakota State Laboratory for identification.
F. tularensis is a fastidious organism and requires cysteine for best growth.
Commercial sheep blood agar may contain cysteine. Cystine enriched chocolate agar, Martin Lewis, Thayer-Martin, cysteine heart agar with blood (CHAB), and buffered charcoal yeast extract agar (BCYE) will support growth of the organism.
|Sheep blood agar (SBA) – Poor growth at 24 hours. At 48 to 72 hours, colonies are 1 to 2 mm, grey-white, and nonhemolytic.|
|Cystine enriched chocolate agar, Martin Lewis agar, or Thayer-Martin agar – colonies, 1 to 3 mm, grey-white at 48 to 72 hours.|
|Cysteine heart agar with blood (CHAB) – Colonies are 2 to 4 mm, smooth, entire, greenish-white, and butyrous with opalescent sheen at 48 to 72 hours.|
|MacConkey agar – no growth.|
|Thioglycollate broth – slow, with denser band near top, diffusing with age.|
|Buffered charcoal yeast extract agar (BCYE) – F. tularensis will grow on BCYE. This media is used for isolation of Legionella and Bordetella pertussis. 1-3mm grey-white colonies at 48 to 72 hours.|