Legionella pneumophila, the etiologic agent of Legionnaires' disease, contains a single, monopolar flagellum which is composed of one major subunit, the FlaA protein. To evaluate the role of the flagellum in the pathogenesis and ecology of Legionella, the flaA gene of L. pneumophila Corby was mutagenized by introduction of a kanamycin resistance cassette. Immunoblots with antiflagellin-specific polyclonal antiserum, electron microscopy, and motility assays confirmed that the specific flagellar mutant L. pneumophila Corby KH3 was nonflagellated. The redelivery of the intact flaA gene into the chromosome (L. pneumophila Corby CD10) completely restored flagellation and motility. Coculture studies showed that the invasion efficiency of the flaA mutant was moderately reduced in amoebae and severely reduced in HL-60 cells. In contrast, adhesion and the intracellular rate of replication remained unaffected. Taking these results together, we have demonstrated that the flagellum of L. pneumophila positively affects the establishment of infection by facilitating the encounter of the host cell as well as by enhancing the invasion capacity.Legionella pneumophila, the etiologic agent of Legionnaires' disease, is a ubiquitous microorganism inhabiting natural and man-made freshwater biotopes (5). In these environments, the gram-negative, rod-shaped bacteria survive as intracellular pathogens of protozoan organisms such as Acanthamoeba castellanii, Hartmannella vermiformis, and Naegleria spp. (15). Upon transmission to individuals via L. pneumophila-containing aerosols generated by showerheads and air-conditioning systems, the bacteria invade and multiply within alveolar macrophages (1, 2, 7) and nonphagocytic cells (17). The infection which mainly affects immunocompromised patients results in a life-threatening atypical pneumonia (7).Detailed ultrastructural and molecular studies of the intracellular fate of the bacterium revealed that human macrophages and protozoan cells infected with L. pneumophila exhibit remarkable similarities concerning the establishment of a replicative phagosome (3,16,22,42,45). However, significant differences were observed during early stages of infection (21). Uptake by Hartmannella is accomplished by a microfilamentindependent mechanism that is sensitive to methylamine, which is an inhibitor of receptor-mediated endocytosis (28). So far, one receptor of Hartmanella vermiformis, a Gal/GalNAc lectin, could be identified (46). Attachment of L. pneumophila to this lectin results in tyrosine dephosphorylation of multiple host cell proteins. However, depending on the type of amoeba, different receptors might be involved (22). In contrast, the uptake by human macrophages occurs following binding of complement receptors CR1 and CR3 via microfilament-dependent phagocytosis (26). In addition to this cytochalasin D-sensitive mechanism, complement-independent mechanisms for uptake by nonphagocytic cells have been described (39).The influence of bacterial motility on infection processes or on survival of legio...

The fliA gene of Legionella pneumophila encoding the alternative 28 factor was inactivated by introducing a kanamycin resistance cassette. Electron microscopy and Western blot analysis revealed that the fliA mutant strain is aflagellate and expresses no flagellin. Reporter gene assays indicated that the flaA promoter is not active in the fliA mutant strain. The fliA mutant strain multiplied less effectively in coculture with amoebae than the wild-type strain and was not able to replicate in coculture with Dictyostelium discoideum.

Cytogenetic analysis of short-term cultures from 15 cases of benign proliferative breast disease (PBD), 10 diffuse PBD and 5 papillomas, and 15 fibroadenomas of the breast revealed clonal chromosome abnormalities in 7 diffuse PBD lesions, 4 papillomas and 5 fibroadenomas. The remaining 14 cases had a normal female chromosome complement. Cytogenetically unrelated abnormal clones were seen in 4 fibroadenomas and 2 PBDs. A single abnormal clone was found in 9 PBDs and 1 fibroadenoma. Three clonal abnormalities were seen as recurrent changes in 6 cases, namely interstitial deletions of 3p with 3p 12-14 as the minimally common deleted segment (in 1 papilloma, 1 diffuse PBD with atypia and 1 mixed-pattern lesion with both papilloma and atypical diffuse PBD features), r(9)(p24q34) (in 1 diffuse PBD and 1 fibroadenoma), and del(1)(q12)(again in 1 diffuse PBD and 1 fibroadenoma). Intriguingly, 6 of the 16 abnormal cases had chromosome changes that have been seen repeatedly as primary abnormalities in breast carcinomas: der(16)t(1;16)(q10;p10), del(3)(p12p14), and del(1)(q12). We conclude that some of the chromosome anomalies frequently found in breast carcinomas are also present in PBD and fibroadenomas. These aberrations may be accepted as early, neoplasia-relevant mutations. However, they do not seem to be sufficient by themselves to unleash a malignant process.

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