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South Dakota Department of Health
South Dakota Department of Health

Laboratory

Francisella Tularensis

Specimen Source

May be isolated from:

  • Blood
  • Sputum
  • Bronchial washings
  • Lymph nodes
  • Wounds
  • Skin lesion exudates

These specimens present an exposure risk to the laboratorian. 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.

Gram Stain

Culture

  • Tiny, pleomorphic, poorly staining gram-negative coccobacillus (0.2 to 0.5 by 0.7 to 1.0 microns). In clinical specimens, these forms can be found intracellularly.
  • Seen mostly as single cells.
  • Bipolar staining is not a distinctive feature.

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.

Choc
Cystine enriched chocolate agar, Martin Lewis agar, or Thayer-Martin agar – colonies, 1 to 3 mm, grey-white at 48 to 72 hours.

Cysteine
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  . 1-3mm grey-white colonies at 48 to 72 hours.

Key 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.

  • Gram-negative, tiny pleomorphic, poorly staining, coccobacillus.
  • Sheep blood agar – grows poorly with very tiny colonies.
  • Chocolate agar (cystine enriched) – grows slowly.
  • Oxidase negative.
  • Nonmotile.
  • Urease negative.
  • Beta-lactamase positive.
  • X and V factors are not required.

Pitfalls

  • Not in the database of most commercial systems.
  • Caution: This organism looks like Haemophilus, but do not smell it. F. tularensis has been reported to cross intact skin. Leave lids on plates.

Look-a-likes

  • H. influenzae
  • Acinetobacter
  • Actinobacillus
  • H. aphrophilus
  • Pasturella
  • Bordetella
  • Group IV
  • Capnocytophaga
  • Kingella
  • Legionella

ID Flow Chart Quick Reference Guide

Safety

  • 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.
  • Use biosafety level 2 practices for specimen processing.
  • Use biosafety level 3 practices for all activities involving manipulations of cultures

Learn How to Submit Isolates