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FrancisellaRANK: GenusTAXONOMY: cellular organisms -> Bacteria -> Proteobacteria -> Gammaproteobacteria -> Thiotrichales -> Francisellaceae -> Francisella OVERVIEW: Short, rod-shaped or coccoid cells, 0.2–0.7 × 0.2 µm (Francisella tularensis subsp. tularensis, F. tularensis subsp. holarctica, and F. tularensis subsp. mediasiatica) or 0.7 × 1.7 µm (F. philomiragia and F. tularensis subsp. novicida) when examined during active growth, pleomorphism occurs thereafter. Gram negative, faintly staining. Endospores are not produced. Nonmotile. Aerobic, growth enhanced under microaerophilic conditions. Colonies are distinct, convex, pale white, and reach maximum size in 3–4 days. Cysteine (or cystine) is required for growth (F. tularensis subsp. tularensis, F. tularensis subsp. holarctica, and F. tularensis subsp. mediasiatica) or enhances growth (F. philomiragia and F. tularensis subsp. novicida). Weakly catalase positive. F. tularensis is oxidase negative and F. philomiragia oxidase positive (Kovacs modification). H2S is produced in cysteine-supplemented medium. Strains from both species, with the exception of F. tularensis subsp. mediasiatica, produce acid but no gas from d-glucose and maltose. Urease negative and no reduction of nitrate. Strains are characterized by a unique fatty acid composition; long-chain saturated and monosaturated C18 to C26 acids, relatively large amounts of saturated even-chain acids (C10:0, C14:0, and C16:0), and two long-chain hydroxy acids (C16:0 3OH and C18:0 3OH).Type species: Francisella tularensis |