Francisella tularensis are GRAM NEGATIVE rods, non-motile and obligately aerobic. When grown on glucose-cysteine-blood agar they form smooth gray colonies; if you let these colonies grow for up to 4 days they will be surrounded by a green zone while discoloring the agar but should not grow over 5 mm in diameter. F. tularensis requires cysteine (or cystine) for growth (if it grows without Cys then it is unlikely F. tularensis) and releases H2S. It is only weakly catalase positive and oxidase negative. There are at least two biovars of tularensis (tularensis and palaearctica) which differ only on whether they produce acid from glycerol and exhibit citrulline ureidase. Subspecies have been proposed for some Central Asian strains. Please let me impress on you how careful you should be with suspected Francisella tularensis strains! If you have the capability you should also look to see if there is a capsule present (and note how large it is relative to the rod).

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