The bacterium Bdellovibrio (Greek bdella,leech) a small, curved, motile rod, has the unique ability to parast oteria (see Bdellovibrio parasitism, page 429).Parasitic strains of this bacterium attack gram-negative organisms, inserting themsehes into the periplasm between the cell wall and membrane. Within this narrow space, the bacterium utilizes the host cell as a substrate