A prospective clinical study of 40 cases of legionnaires' disease combined with serial laboratory examinations enabled us to present an update as well as new recommendations concerning the use of diagnostic tests for legionnaires' disease. Transtracheal aspirate specimens are the optimal specimen for recovery of Legionella pneumophila by culture as well as the most sensitive method for early diagnosis. In addition, with recent improvements in culture media and methodology, L pneumophila can now be readily isolated from sputum. Examination of respiratory specimens by direct immunofluorescence (DFA) is useful, but the sensitivity is much less than that of culture. The yield from DFA examination directly correlates with the number of L pneumophila recoverable by cultural methods; thus, the DFA test result may be negative in an early or mild case of legionnaires' disease. Antibody titers were elevated in 27% of cases within one week of onset of pneumonia and may, therefore, be useful in early diagnosis in selected patients.

Five strains of bacteria (strains 684, 687, U7W, U8W, and MICU-B) that were biochemically and morphologically indistinguishable from Legionella pneumophila were recovered from the environment. Strains U7W, U8W, and MICU-B were antigenically identical to L. pneumophila strain Dallas 1E (serogroup 5), as determined by direct fluorescent antibody staining and immunodiffusion. Although strains 694 and 687 shared antigenic determinants with L. pneumophila Dallas 1E, they could be distinguished by immunodiffusion and differential absorption studies. However, as determined by DNA hybridization, the antigenically distinct strains 684 and 687 belong to the same DNA homology cluster as previously described authentic strains of L. pneumophila, whereas strains U7W, U8W, and MICU-B belong to a separate homology group. Therefore, two groups could be identified among these environmental isolates; one represents an antigenic subclass of serogroup 5 L. pneumophila (strains 684 and 687), and the other, although antigenically indistinguishable from serogroup 5 L. pneumophila, probably represents a new Legionella species (strains U7W, U8W, and MICU-B).

The structure of five parasitic strains of Bdellovibrio bacteriovorus was studied by electron microscope after negative staining and in shadow-case and etched freezefractured preparations. Special attention was paid to the cell wall and the flagellar sheath which is continuous with the wall or part of it. These structural components reveal distinct features which are induced by certain staining substances; they are exceedingly susceptible to disruption by physical treatments, and in old cells often appear impaired. In freeze-fractured cells the wall shows characteristic fracturing tendencies not known in other microorganisms. These structural properties and features are distinct to Bdellovibrio wall and flagellar sheath, the structural integrity of which is a fundamental requirement for the infectivity and survival of this organism. The anterior end of Bdellovibrio is differentiated: 6 to 12 ring-like structures (9 to 12 nm, outer diameter) are built into its wall and several fibers (7 to 10 nm wide, up to 1.5 ,um long) emerge from it. Intracellular structures, which are revealed as compact oval bodies bulging from the cell border and have internal laminated organization, are characteristic of Bdellovibrio after negative staining with certain compounds. These findings on the structure of parasitic Bdellovibrio substantiate previous observations indicating the uniqueness of this organism and add criteria for the identification of this genus. Proc., p. 41, 1967). MATERIALS AND METHODS Organisms. Five strains of B. bacteriovorus were employed: 109 and D (obtained from M.

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