Legionella pneumophila pathogesesis: a fateful journey from amoebae to macrophages.

Legionella pneumophila first commanded attention in 1976, when investigators from the Centers for Disease Control and Prevention identified it as the culprit in a massive outbreak of pneumonia that struck individuals attending an American Legion convention (). It is now clear that this gram-negative bacterium flourishes naturally in fresh water as a parasite of amoebae, but it can also replicate within alveolar macrophages. L. pneumophila pathogenesis is discussed using the following model as a framework. When ingested by phagocytes, stationary-phase L. pneumophila bacteria establish phagosomes which are completely isolated from the endosomal pathway but are surrounded by endoplasmic reticulum. Within this protected vacuole, L. pneumophila converts to a replicative form that is acid tolerant but no longer expresses several virulence traits, including factors that block membrane fusion. As a consequence, the pathogen vacuoles merge with lysosomes, which provide a nutrient-rich replication niche. Once the amino acid supply is depleted, progeny accumulate the second messenger guanosine 3',5'-bispyrophosphate (ppGpp), which coordinates entry into the stationary phase with expression of traits that promote transmission to a new phagocyte. A number of factors contribute to L. pneumophila virulence, including type II and type IV secretion systems, a pore-forming toxin, type IV pili, flagella, and numerous other factors currently under investigation. Because of its resemblance to certain aspects of Mycobacterium, Toxoplasma, Leishmania, and Coxiella pathogenesis, a detailed description of the mechanism used by L. pneumophila to manipulate and exploit phagocyte membrane traffic may suggest novel strategies for treating a variety of infectious diseases. Knowledge of L. pneumophila ecology may also inform efforts to combat the emergence of new opportunistic macrophage pathogens.

[1]  B E Dunn,et al.  Surface localization of Helicobacter pylori urease and a heat shock protein homolog requires bacterial autolysis , 1996, Infection and immunity.

[2]  Paul S. Hoffman,et al.  Surface-Associated Hsp60 Chaperonin of Legionella pneumophila Mediates Invasion in a HeLa Cell Model , 1998, Infection and Immunity.

[3]  W. Dunn,et al.  Autophagy and related mechanisms of lysosome-mediated protein degradation. , 1994, Trends in cell biology.

[4]  S. Donnellan,et al.  Interspecies sequence differences in the Mip protein from the genus Legionella: implications for function and evolutionary relatedness , 1997, Molecular microbiology.

[5]  E. Rietschel,et al.  The structure of the O-specific chain of Legionella pneumophila serogroup 1 lipopolysaccharide. , 1994, European journal of biochemistry.

[6]  P. D. Hart,et al.  RESPONSE OF CULTURED MACROPHAGES TO MYCOBACTERIUM TUBERCULOSIS, WITH OBSERVATIONS ON FUSION OF LYSOSOMES WITH PHAGOSOMES , 1971, The Journal of experimental medicine.

[7]  P. Small,et al.  Identification of σs‐dependent genes associated with the stationary‐phase acid‐resistance phenotype of Shigella flexneri , 1996, Molecular microbiology.

[8]  S Dubrou,et al.  The intracellular multiplication of Legionella pneumophila in protozoa from hospital plumbing systems. , 1991, Research in microbiology.

[9]  M. R. Brown,et al.  Unexplored reservoirs of pathogenic bacteria: protozoa and biofilms. , 1999, Trends in microbiology.

[10]  V L Yu,et al.  Mode of transmission of Legionella pneumophila. A critical review. , 1986, Archives of internal medicine.

[11]  B. Marston,et al.  Surveillance for Legionnaires' disease. Risk factors for morbidity and mortality. , 1994, Archives of internal medicine.

[12]  D. Portnoy,et al.  The broad-range phospholipase C and a metalloprotease mediate listeriolysin O-independent escape of Listeria monocytogenes from a primary vacuole in human epithelial cells , 1995, Infection and immunity.

[13]  K. Chang,et al.  Leishmania donovani: promastigote--macrophage surface interactions in vitro. , 1979, Experimental parasitology.

[14]  C. Woese,et al.  Phylogenetic diversity of the Rickettsiae , 1989, Journal of bacteriology.

[15]  Y. Kwaik The phagosome containing Legionella pneumophila within the protozoan Hartmannella vermiformis is surrounded by the rough endoplasmic reticulum. , 1996 .

[16]  M. Horwitz Cell-mediated immunity in Legionnaires' disease. , 1983, The Journal of clinical investigation.

[17]  S. Halling,et al.  Construction of Cu-Zn superoxide dismutase deletion mutants of Brucella abortus: analysis of survival in vitro in epithelial and phagocytic cells and in vivo in mice , 1992, Infection and immunity.

[18]  P. Sansonetti,et al.  Contribution of superoxide dismutase and catalase activities to Shigella flexneri pathogenesis , 1990, Infection and immunity.

[19]  J. Cirillo,et al.  Effects of an isogenic Zn‐metalloprotease‐deficien mutant of Legionella pneumophila in a guinea‐pig pneumonia model , 1994, Molecular microbiology.

[20]  B. Stone,et al.  Natural Competence for DNA Transformation by Legionella pneumophila and Its Association with Expression of Type IV Pili , 1999, Journal of bacteriology.

[21]  R. Heinzen,et al.  Differential interaction with endocytic and exocytic pathways distinguish parasitophorous vacuoles of Coxiella burnetii and Chlamydia trachomatis , 1996, Infection and immunity.

[22]  H. Shuman,et al.  The iron superoxide dismutase of Legionella pneumophila is essential for viability , 1994, Journal of bacteriology.

[23]  W. Johnson,et al.  Interaction of Legionella pneumophila with Acanthamoeba castellanii: uptake by coiling phagocytosis and inhibition of phagosome-lysosome fusion , 1996, Infection and immunity.

[24]  T. Byrd,et al.  Interferon gamma-activated human monocytes downregulate transferrin receptors and inhibit the intracellular multiplication of Legionella pneumophila by limiting the availability of iron. , 1989, The Journal of clinical investigation.

[25]  H. Shuman,et al.  Legionella pneumophila Utilizes the Same Genes To Multiply within Acanthamoeba castellanii and Human Macrophages , 1999, Infection and Immunity.

[26]  J. Hacker,et al.  Sequence determination and mutational analysis of the lly locus of Legionella pneumophila , 1994, Infection and immunity.

[27]  J. Neilands,et al.  Ferric uptake regulation protein acts as a repressor, employing iron (II) as a cofactor to bind the operator of an iron transport operon in Escherichia coli. , 1987, Biochemistry.

[28]  M. Bibb,et al.  The ppGpp synthetase gene (relA) of Streptomyces coelicolor A3(2) plays a conditional role in antibiotic production and morphological differentiation , 1997, Journal of bacteriology.

[29]  J. W. Conlan,et al.  Separation of Legionella pneumophila proteases and purification of a protease which produces lesions like those of Legionnaires' disease in guinea pig lung. , 1986, Journal of general microbiology.

[30]  M. Horwitz,et al.  Interferon-gamma-activated human monocytes inhibit the intracellular multiplication of Legionella pneumophila. , 1986, Journal of immunology.

[31]  R. Miller,et al.  Inhibition of polymorphonuclear leukocyte function by Legionella pneumophila exoproducts. , 1990, Microbial pathogenesis.

[32]  N. Willetts Structure and function of the F factor and mechanism of conjugation , 1987 .

[33]  J. Pruckler,et al.  Association of flagellum expression and intracellular growth of Legionella pneumophila , 1995, Infection and immunity.

[34]  R. J. Carter,et al.  Outbreak of Legionnaires' disease among cruise ship passengers exposed to a contaminated whirlpool spa , 1996, The Lancet.

[35]  Benson Rf,et al.  Classification of the genus Legionella. , 1998 .

[36]  K. Birkness,et al.  Mycobacterium avium Bacilli Grow Saprozoically in Coculture with Acanthamoeba polyphaga and Survive within Cyst Walls , 1998, Applied and Environmental Microbiology.

[37]  A. MacKenzie,et al.  Cloning and characterization of the multiple murine homologues of NAIP (neuronal apoptosis inhibitory protein). , 1998, Genomics.

[38]  D. Remick,et al.  In vivo regulation of replicative Legionella pneumophila lung infection by endogenous tumor necrosis factor alpha and nitric oxide , 1995, Infection and immunity.

[39]  J. Hacker,et al.  Characterization of legiolysin (lly), responsible for haemolytic activity, colour production and fluorescence of Legionella pneumophila , 1991, Molecular microbiology.

[40]  B. Fields,et al.  The molecular ecology of legionellae. , 1996, Trends in microbiology.

[41]  Y. Kwaik,et al.  Identification of a Gal/GalNAc Lectin in the Protozoan Hartmannella vermiformis as a Potential Receptor for Attachment and Invasion by the Legionnaires' Disease Bacterium , 1997, The Journal of experimental medicine.

[42]  S. Lory,et al.  Structure-function and biogenesis of the type IV pili. , 1993, Annual review of microbiology.

[43]  R. Isberg,et al.  Two distinct defects in intracellular growth complemented by a single genetic locus in Legionella pneumophila , 1993, Molecular microbiology.

[44]  E. White,et al.  Effects of cytochalasin D and methylamine on intracellular growth of Legionella pneumophila in amoebae and human monocyte-like cells , 1991, Infection and immunity.

[45]  H. Shuman,et al.  Legionella pneumophila Contains a Type II General Secretion Pathway Required for Growth in Amoebae as Well as for Secretion of the Msp Protease , 1999, Infection and Immunity.

[46]  M. Horwitz,et al.  Phagocytosis of Legionella pneumophila is mediated by human monocyte complement receptors , 1987, The Journal of experimental medicine.

[47]  P. Brachman,et al.  Legionnaires' disease. , 1977, Disease-a-month : DM.

[48]  M. Cashel,et al.  The stringent response , 1996 .

[49]  J. Foster Low pH adaptation and the acid tolerance response of Salmonella typhimurium. , 1995, Critical reviews in microbiology.

[50]  T. Klein,et al.  Differential morphologic and metabolic alterations in permissive versus nonpermissive murine macrophages infected with Legionella pneumophila , 1992, Infection and immunity.

[51]  K. Heuner,et al.  Cloning and genetic characterization of the flagellum subunit gene (flaA) of Legionella pneumophila serogroup 1 , 1995, Infection and immunity.

[52]  P. Lambert,et al.  Influence of intra-amoebic and other growth conditions on the surface properties of Legionella pneumophila , 1993, Infection and immunity.

[53]  P. Hoffman,et al.  Legionella pneumophila htpAB heat shock operon: nucleotide sequence and expression of the 60-kilodalton antigen in L. pneumophila-infected HeLa cells , 1990, Infection and immunity.

[54]  N. Vats,et al.  Immunolocalization of Hsp60 inLegionella pneumophila , 1998, Journal of bacteriology.

[55]  P. Edelson,et al.  EFFECTS OF CONCANAVALIN A ON MOUSE PERITONEAL MACROPHAGES , 1974, The Journal of experimental medicine.

[56]  R. Friis Interaction of L Cells and Chlamydia psittaci: Entry of the Parasite and Host Responses to Its Development , 1972, Journal of bacteriology.

[57]  F. Fang,et al.  Growth-phase regulation of plasmid virulence genes in Salmonella. , 1995, Trends in microbiology.

[58]  W. Baine,et al.  A phospholipase C from the Dallas 1E strain of Legionella pneumophila serogroup 5: purification and characterization of conditions for optimal activity with an artificial substrate. , 1988, Journal of general microbiology.

[59]  M. Horwitz,et al.  Characterization of the Mycobacterium tuberculosis phagosome and evidence that phagosomal maturation is inhibited , 1995, The Journal of experimental medicine.

[60]  S. L. Morris,et al.  Identification of a 68 kd surface antigen of Mycobacterium avium that binds to human macrophages. , 1994, The Journal of laboratory and clinical medicine.

[61]  E. Hickey,et al.  An iron- and fur-repressed Legionella pneumophila gene that promotes intracellular infection and encodes a protein with similarity to the Escherichia coli aerobactin synthetases , 1997, Infection and immunity.

[62]  M. R. Brown,et al.  Relationship between Legionella pneumophila and Acanthamoeba polyphaga: physiological status and susceptibility to chemical inactivation , 1992, Applied and environmental microbiology.

[63]  R. Breiman,et al.  Association of shower use with Legionnaires' disease. Possible role of amoebae. , 1990, JAMA.

[64]  N. Cianciotto,et al.  Legionella pneumophila mutants that are defective for iron acquisition and assimilation and intracellular infection , 1996, Infection and immunity.

[65]  D. Kaiser,et al.  The guanosine nucleotide (p)ppGpp initiates development and A-factor production in myxococcus xanthus. , 1998, Genes & development.

[66]  C. Newton,et al.  Immunologic response and pathophysiology of Legionella infection. , 1998, Seminars in respiratory infections.

[67]  J. Hacker,et al.  Evidence for apoptosis of human macrophage-like HL-60 cells by Legionella pneumophila infection , 1996, Infection and immunity.

[68]  J. Dixon,et al.  Protein tyrosine phosphatase activity of an essential virulence determinant in Yersinia. , 1990, Science.

[69]  P. Schlesinger,et al.  Parasitophorous vacuoles of Leishmania mexicana acquire macromolecules from the host cell cytosol via two independent routes. , 1999, Journal of cell science.

[70]  A. Wandinger-Ness,et al.  Rab 7: an important regulator of late endocytic membrane traffic , 1995, The Journal of cell biology.

[71]  W. Goebel,et al.  Expression and use of the green fluorescent protein as a reporter system in Legionella pneumophila , 2000, Molecular and General Genetics MGG.

[72]  J. Costerton,et al.  Bacterial biofilms: a common cause of persistent infections. , 1999, Science.

[73]  C. Mody,et al.  A mutation in the mip gene results in an attenuation of Legionella pneumophila virulence. , 1990, The Journal of infectious diseases.

[74]  O. Harb,et al.  Transcriptional regulation of the macrophage‐induced gene (gspA) of Legionella pneumophila and phenotypic characterization of a null mutant , 1997, Molecular microbiology.

[75]  H. Scaife,et al.  Intraphagocytic growth induces an antibiotic-resistant phenotype of Legionella pneumophila , 1995, Antimicrobial agents and chemotherapy.

[76]  P. Hoffman,et al.  Characterization of a Legionella pneumophila extracellular protease exhibiting hemolytic and cytotoxic activities , 1989, Infection and immunity.

[77]  Y. Abu Kwaik,et al.  Apoptosis in Macrophages and Alveolar Epithelial Cells during Early Stages of Infection by Legionella pneumophila and Its Role in Cytopathogenicity , 1999, Infection and Immunity.

[78]  F. D. Johnson,et al.  Molecular characterization of an operon required for pertussis toxin secretion. , 1993, Proceedings of the National Academy of Sciences of the United States of America.

[79]  G F Mallison,et al.  An outbreak of Legionnaires' disease associated with a contaminated air-conditioning cooling tower. , 1980, The New England journal of medicine.

[80]  B. Beaman,et al.  Monoclonal antibodies demonstrate that superoxide dismutase contributes to protection of Nocardia asteroides within the intact host , 1990, Infection and immunity.

[81]  R. Isberg,et al.  Identification of Linked Legionella pneumophila Genes Essential for Intracellular Growth and Evasion of the Endocytic Pathway , 1998, Infection and Immunity.

[82]  A. Ishihama,et al.  RpoS (Sigma-S) Controls Expression of rsmA, a Global Regulator of Secondary Metabolites, Harpin, and Extracellular Proteins in Erwinia carotovora , 1998, Journal of bacteriology.

[83]  J. Armstrong,et al.  Prevention of phagosome-lysosome fusion in cultured macrophages by sulfatides of Mycobacterium tuberculosis. , 1976, Proceedings of the National Academy of Sciences of the United States of America.

[84]  R. D. Smith,et al.  Production of mouse monoclonal antibodies which inhibit in vitro adherence of Entamoeba histolytica trophozoites , 1986, Infection and immunity.

[85]  S. Yoshida,et al.  Genetic control of natural resistance in mouse macrophages regulating intracellular Legionella pneumophila multiplication in vitro , 1991, Infection and immunity.

[86]  E. Lander,et al.  Lgn1, a gene that determines susceptibility to Legionella pneumophila, maps to mouse chromosome 13. , 1995, Genomics.

[87]  M. Spector The starvation-stress response (SSR) of Salmonella. , 1998, Advances in microbial physiology.

[88]  H. Shuman,et al.  Host cell killing and bacterial conjugation require overlapping sets of genes within a 22-kb region of the Legionella pneumophila genome. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[89]  F. Maxfield,et al.  Legionella pneumophila inhibits acidification of its phagosome in human monocytes , 1984, The Journal of cell biology.

[90]  P. Gros,et al.  The Neuronal Apoptosis Inhibitory Protein (Naip) Is Expressed in Macrophages and Is Modulated After Phagocytosis and During Intracellular Infection with Legionella pneumophila1 , 2000, The Journal of Immunology.

[91]  J. Sýkora,et al.  Growth-supporting activity for Legionella pneumophila in tap water cultures and implication of hartmannellid amoebae as growth factors , 1988, Applied and environmental microbiology.

[92]  R. Isberg,et al.  Analysis of the Legionella pneumophila fliI gene: intracellular growth of a defined mutant defective for flagellum biosynthesis , 1997, Infection and immunity.

[93]  G. Burmester,et al.  Coiling phagocytosis: when the zipper jams, the cup is deformed. , 1998, Trends in microbiology.

[94]  M. Liles,et al.  Discovery of a Nonclassical Siderophore, Legiobactin, Produced by Strains of Legionella pneumophila , 2000, Journal of bacteriology.

[95]  C. Mody,et al.  A Legionella pneumophila gene encoding a species-specific surface protein potentiates initiation of intracellular infection , 1989, Infection and immunity.

[96]  N. Engleberg,et al.  Phenotypic modulation by Legionella pneumophila upon infection of macrophages , 1993, Infection and immunity.

[97]  T. Martin,et al.  Alveolar macrophage activation in experimental legionellosis. , 1991, Journal of immunology.

[98]  E. Hickey,et al.  Cloning and sequencing of the Legionella pneumophila fur gene. , 1994, Gene.

[99]  H. Steinman,et al.  Legionella pneumophilaCatalase-Peroxidases: Cloning of the katB Gene and Studies of KatB Function , 1998, Journal of bacteriology.

[100]  J. Weinberg,et al.  Internucleosomal DNA cleavage triggered by plasma membrane damage during necrotic cell death. Involvement of serine but not cysteine proteases. , 1997, The American journal of pathology.

[101]  M. Loos,et al.  A 66-kilodalton heat shock protein of Salmonella typhimurium is responsible for binding of the bacterium to intestinal mucus , 1992, Infection and immunity.

[102]  S. Falkow,et al.  Coordinate regulation and sensory transduction in the control of bacterial virulence. , 1989, Science.

[103]  M. Swanson,et al.  Identification of Legionella pneumophila mutants that have aberrant intracellular fates , 1996, Infection and immunity.

[104]  M. Horwitz,et al.  Complement component C3 fixes selectively to the major outer membrane protein (MOMP) of Legionella pneumophila and mediates phagocytosis of liposome-MOMP complexes by human monocytes , 1990, The Journal of experimental medicine.

[105]  T. Byrd,et al.  Regulation of transferrin receptor expression and ferritin content in human mononuclear phagocytes. Coordinate upregulation by iron transferrin and downregulation by interferon gamma. , 1993, The Journal of clinical investigation.

[106]  J. Hacker,et al.  Temperature-dependent expression of flagella in Legionella. , 1991, Journal of general microbiology.

[107]  G. Robertson,et al.  Elevation of neuronal expression of NAIP reduces ischemic damage in the rat hippocampus , 1997, Nature Medicine.

[108]  M. Horwitz Formation of a novel phagosome by the Legionnaires' disease bacterium (Legionella pneumophila) in human monocytes , 1983, The Journal of experimental medicine.

[109]  J. Brieland,et al.  Different fates ofLegionella pneumophila pmiandmilmutants within macrophages and alveolar epithelial cells , 1998 .

[110]  A. Binns,et al.  Inhibition of VirB-mediated transfer of diverse substrates from Agrobacterium tumefaciens by the IncQ plasmid RSF1010 , 1995, Journal of bacteriology.

[111]  E. Groisman,et al.  Mg2+ as an Extracellular Signal: Environmental Regulation of Salmonella Virulence , 1996, Cell.

[112]  T. Yamamoto,et al.  Induction of Yersinia enterocolitica Stress Proteins by Phagocytosis with Macrophage , 1994, Microbiology and immunology.

[113]  T. Rowbotham,et al.  Preliminary report on the pathogenicity of Legionella pneumophila for freshwater and soil amoebae. , 1980, Journal of clinical pathology.

[114]  F. Fang,et al.  The alternative sigma factor katF (rpoS) regulates Salmonella virulence. , 1992, Proceedings of the National Academy of Sciences of the United States of America.

[115]  M. Horwitz,et al.  Membrane sorting during phagocytosis: selective exclusion of major histocompatibility complex molecules but not complement receptor CR3 during conventional and coiling phagocytosis , 1992, The Journal of experimental medicine.

[116]  N. Cianciotto,et al.  The Legionella pneumophila iraAB Locus Is Required for Iron Assimilation, Intracellular Infection, and Virulence , 2000, Infection and Immunity.

[117]  M. Russel Macromolecular assembly and secretion across the bacterial cell envelope: type II protein secretion systems. , 1998, Journal of molecular biology.

[118]  R. Isberg,et al.  Legionella pneumophila DotA protein is required for early phagosome trafficking decisions that occur within minutes of bacterial uptake , 1998, Molecular microbiology.

[119]  J. Rowatt,et al.  Lysosomal response of a murine macrophage-like cell line persistently infected with Coxiella burnetii , 1983, Infection and immunity.

[120]  J. Feeley,et al.  Pontiac fever: isolation of the etiologic agent (Legionella pneumophilia) and demonstration of its mode of transmission. , 1981, American journal of epidemiology.

[121]  J. Hacker,et al.  Legionella pneumophila kills human phagocytes but not protozoan host cells by inducing apoptotic cell death. , 1998, FEMS microbiology letters.

[122]  H. Shuman,et al.  Intracellular multiplication and human macrophage killing by Legionella pneumophila are inhibited by conjugal components of IncQ plasmid RSF1010 , 1998, Molecular microbiology.

[123]  O. Harb,et al.  Heterogeneity in the Attachment and Uptake Mechanisms of the Legionnaires’ Disease Bacterium, Legionella pneumophila, by Protozoan Hosts , 1998, Applied and Environmental Microbiology.

[124]  J. Köhl,et al.  Phase-variable Expression of Lipopolysaccharide Contributes to the Virulence of Legionella pneumophila , 1998, The Journal of experimental medicine.

[125]  H. Shuman,et al.  Possible origin of the Legionella pneumophila virulence genes and their relation to Coxiella burnetii , 1999, Molecular microbiology.

[126]  C. Bogdan,et al.  Coiling Phagocytosis of Trypanosomatids and Fungal Cells , 1998, Infection and Immunity.

[127]  M. Cashel,et al.  Synthesis of the stationary-phase sigma factor sigma s is positively regulated by ppGpp , 1993, Journal of bacteriology.

[128]  P. Edelstein,et al.  Influence of growth temperature on virulence of Legionella pneumophila , 1987, Infection and immunity.

[129]  J. Brieland,et al.  Replicative Legionella pneumophila lung infection in intratracheally inoculated A/J mice. A murine model of human Legionnaires' disease. , 1994, The American journal of pathology.

[130]  M. Horwitz,et al.  Interaction between the legionnaires' disease bacterium (Legionella pneumophila) and human alveolar macrophages. Influence of antibody, lymphokines, and hydrocortisone. , 1984, The Journal of clinical investigation.

[131]  M. Marahiel,et al.  Cloning and characterization of a relA/spoT homologue from Bacillus subtilis , 1997, Molecular microbiology.

[132]  N. Cianciotto,et al.  Legionella pneumophila mip gene potentiates intracellular infection of protozoa and human macrophages. , 1992, Proceedings of the National Academy of Sciences of the United States of America.

[133]  D. Raoult,et al.  Phagolysosomes of Coxiella burnetii-infected cell lines maintain an acidic pH during persistent infection , 1992, Infection and immunity.

[134]  R. Isberg,et al.  Conjugative transfer by the virulence system of Legionella pneumophila. , 1998, Science.

[135]  M. Liles,et al.  Identification and Temperature Regulation ofLegionella pneumophila Genes Involved in Type IV Pilus Biogenesis and Type II Protein Secretion , 1998, Infection and Immunity.

[136]  T. Lagergård,et al.  GroEL Heat Shock Protein of Haemophilus ducreyi: Association with Cell Surface and Capacity To Bind to Eukaryotic Cells , 1998, Infection and Immunity.

[137]  M. Borodovsky,et al.  cag, a pathogenicity island of Helicobacter pylori, encodes type I-specific and disease-associated virulence factors. , 1996, Proceedings of the National Academy of Sciences of the United States of America.

[138]  H. Steinman,et al.  Periplasmic copper-zinc superoxide dismutase of Legionella pneumophila: role in stationary-phase survival , 1996, Journal of bacteriology.

[139]  O. Harb,et al.  Utilization of similar mechanisms by Legionella pneumophila to parasitize two evolutionarily distant host cells, mammalian macrophages and protozoa , 1997, Infection and immunity.

[140]  Samuel L. Groseclose,et al.  Summary of Notifiable Diseases, United States. , 1997 .

[141]  F. Heffron,et al.  Induction of Salmonella stress proteins upon infection of macrophages. , 1990, Science.

[142]  N. Thornberry,et al.  Inhibition of Human Caspases by Peptide-based and Macromolecular Inhibitors* , 1998, The Journal of Biological Chemistry.

[143]  C. E. Haley,et al.  Nosocomial Legionnaires' disease: a continuing common-source epidemic at Wadsworth Medical Center. , 1979, Annals of internal medicine.

[144]  B. Stone,et al.  Expression of Multiple Pili by Legionella pneumophila: Identification and Characterization of a Type IV Pilin Gene and Its Role in Adherence to Mammalian and Protozoan Cells , 1998, Infection and Immunity.

[145]  J. Brieland,et al.  Coinoculation with Hartmannella vermiformis enhances replicative Legionella pneumophila lung infection in a murine model of Legionnaires' disease , 1996, Infection and immunity.

[146]  J. Mekalanos,et al.  Genetic regulation of bacterial virulence. , 1989, Annual review of genetics.

[147]  S. Pfeffer,et al.  Rab7 and Rab9 Are Recruited onto Late Endosomes by Biochemically Distinguishable Processes (*) , 1995, The Journal of Biological Chemistry.

[148]  C. Keevil,et al.  Growth temperature reversibly modulates the virulence of Legionella pneumophila , 1994, Infection and immunity.

[149]  S. Lory,et al.  Nucleotide sequence and transcriptional initiation site of two Pseudomonas aeruginosa pilin genes. , 1986, The Journal of biological chemistry.

[150]  B. Iglewski,et al.  The effects of Legionella pneumophila toxin on oxidative processes and bacterial killing of human polymorphonuclear leukocytes. , 1982, The Journal of infectious diseases.

[151]  P. Christie Agrobacterium tumefaciens T-complex transport apparatus: a paradigm for a new family of multifunctional transporters in eubacteria , 1997, Journal of bacteriology.

[152]  B. Iglewski,et al.  Defective triggering of polymorphonuclear leukocyte oxidative metabolism by Legionella pneumophila toxin. , 1985, The Journal of infectious diseases.

[153]  F. Maxfield,et al.  Early Events in Phagosome Establishment Are Required for Intracellular Survival of Legionella pneumophila , 1998, Infection and Immunity.

[154]  H. Shuman,et al.  Characterization of a new region required for macrophage killing by Legionella pneumophila , 1997, Infection and immunity.

[155]  M. Horwitz The Legionnaires' disease bacterium (Legionella pneumophila) inhibits phagosome-lysosome fusion in human monocytes , 1983, The Journal of experimental medicine.

[156]  P. Hoffman,et al.  Cloning and nucleotide sequence of a gene (ompS) encoding the major outer membrane protein of Legionella pneumophila , 1992, Journal of bacteriology.

[157]  M. Pallen,et al.  Bacterial copper‐ and zinc‐cofactored superoxide dismutase contributes to the pathogenesis of systemic salmonellosis , 1997, Molecular microbiology.

[158]  M. Swanson,et al.  Association of Legionella pneumophila with the macrophage endoplasmic reticulum , 1995, Infection and immunity.

[159]  S. Falkow,et al.  Growth of Legionella pneumophila in Acanthamoeba castellanii enhances invasion , 1994, Infection and immunity.

[160]  J. Craighead,et al.  Ultrastructure of lung in Legionnaires' disease. Observations of three biopsies done during the Vermont epidemic. , 1979, Annals of internal medicine.

[161]  J. Blom,et al.  Engulfment of the Philadelphia strain of Legionella pneumophila within pseudopod coils in human phagocytes , 1989, APMIS : acta pathologica, microbiologica, et immunologica Scandinavica.

[162]  A. Kharazmi,et al.  Effect of Legionella pneumophila cytotoxic protease on human neutrophil and monocyte function. , 1992, Microbial pathogenesis.

[163]  N. Cheville,et al.  Ultrastructural morphometric analysis of Brucella abortus-infected trophoblasts in experimental placentitis. Bacterial replication occurs in rough endoplasmic reticulum. , 1986, The American journal of pathology.

[164]  W. Baine Cytolytic and phospholipase C activity in Legionella species. , 1985, Journal of general microbiology.

[165]  J. Mekalanos Environmental signals controlling expression of virulence determinants in bacteria , 1992, Journal of bacteriology.

[166]  M. Liles,et al.  The prepilin peptidase is required for protein secretion by and the virulence of the intracellular pathogen Legionella pneumophila , 1999, Molecular microbiology.

[167]  H. Shuman,et al.  Identification of Legionella pneumophila genes required for growth within and killing of human macrophages , 1993, Infection and immunity.

[168]  W. Johnson,et al.  Cytotoxicity of extracellular Legionella pneumophila , 1994, Infection and immunity.

[169]  J. Ellis Proteins as molecular chaperones , 1987, Nature.

[170]  M. Horwitz,et al.  Characterization of avirulent mutant Legionella pneumophila that survive but do not multiply within human monocytes , 1987, The Journal of experimental medicine.

[171]  J. G. Hirsch,et al.  THE INTERACTION BETWEEN TOXOPLASMA GONDII AND MAMMALIAN CELLS , 1972, The Journal of experimental medicine.

[172]  C. R. Bagnell,et al.  Vesicles containing Chlamydia trachomatis serovar L2 remain above pH 6 within HEC-1B cells , 1996, Infection and immunity.

[173]  J. Barbaree,et al.  Isolation of protozoa from water associated with a legionellosis outbreak and demonstration of intracellular multiplication of Legionella pneumophila , 1986, Applied and environmental microbiology.

[174]  M. Šuša,et al.  Heterogeneity in intracellular replication and cytopathogenicity of Legionella pneumophila and Legionella micdadei in mammalian and protozoan cells. , 1999, Microbial pathogenesis.

[175]  J. Dowling,et al.  Interaction of Legionella micdadei with human monocytes , 1984, Infection and immunity.

[176]  F. Rodgers,et al.  Role of the 25 kDa major outer membrane protein of Legionella pneumophila in attachment to U‐937 cells and its potential as a virulence factor for chick embryos , 1999, Journal of applied microbiology.

[177]  R. Heinzen,et al.  Developmental biology of Coxiella burnettii. , 1999, Trends in microbiology.

[178]  J. Coers,et al.  Modulation of phagosome biogenesis by Legionella pneumophila creates an organelle permissive for intracellular growth , 1999, Nature Cell Biology.

[179]  E. Linder,et al.  Free-living amoebae protecting Legionella in water: the tip of an iceberg? , 1999, Scandinavian journal of infectious diseases.

[180]  R. Myerowitz,et al.  The pathology of the Legionella pneumonias. A review of 74 cases and the literature. , 1981, Human pathology.

[181]  S Falkow,et al.  Interaction of Mycobacterium avium with environmental amoebae enhances virulence , 1997, Infection and immunity.

[182]  M. Swanson,et al.  Comparative Analysis of Legionella pneumophila and Legionella micdadeiVirulence Traits , 1999, Infection and Immunity.

[183]  L. Sibley,et al.  Intracellular fate of vacuoles containing Toxoplasma gondii is determined at the time of formation and depends on the mechanism of entry. , 1997, Journal of immunology.

[184]  Y. Kwaik,et al.  The use of differential display‐PCR to isolate and characterize a Legionella pneumophila locus induced during the intracellular infection of macrophages , 1996, Molecular microbiology.

[185]  K. Heuner,et al.  The expression of the flagellum of Legionella pneumophila is modulated by different environmental factors. , 1999, FEMS microbiology letters.

[186]  J. Pearce,et al.  Chlamydia trachomatis Mip‐like protein has peptidylprolyl cis/trans isomerase activity that is inhibited by FK506 and rapamycin and is implicated in initiation of chlamydial infection , 1993, Molecular microbiology.

[187]  M. Horwitz,et al.  Interaction of the legionnaires' disease bacterium (Legionella pneumophila) with human phagocytes. II. Antibody promotes binding of L. pneumophila to monocytes but does not inhibit intracellular multiplication , 1981, The Journal of experimental medicine.

[188]  A. Tzianabos,et al.  Adherence of Legionella pneumophila to U-937 cells, guinea-pig alveolar macrophages, and MRC-5 cells by a novel, complement-independent binding mechanism. , 1994, Canadian journal of microbiology.

[189]  A. Descoteaux,et al.  The lipophosphoglycan of Leishmania parasites. , 1992, Annual review of microbiology.

[190]  S. C. Winans,et al.  Adaptation of a conjugal transfer system for the export of pathogenic macromolecules. , 1996, Trends in microbiology.

[191]  J. Slonczewski,et al.  Acid and base resistance in Escherichia coli and Shigella flexneri: role of rpoS and growth pH , 1994, Journal of bacteriology.

[192]  M. Endrizzi,et al.  The mouse Naip gene cluster on Chromosome 13 encodes several distinct functional transcripts , 1999, Mammalian Genome.

[193]  H. Reynolds,et al.  Analysis of proteins and respiratory cells obtained from human lungs by bronchial lavage. , 1974, The Journal of laboratory and clinical medicine.

[194]  B. Iglewski,et al.  Purification and characterization of an extracellular protease of Legionella pneumophila , 1986, Infection and immunity.

[195]  C. Roy,et al.  Pore‐forming activity is not sufficient for Legionella pneumophila phagosome trafficking and intracellular growth , 1999, Molecular microbiology.

[196]  D. O’Callaghan,et al.  A homologue of the Agrobacterium tumefaciens VirB and Bordetella pertussis Ptl type IV secretion systems is essential for intracellular survival of Brucella suis , 1999, Molecular microbiology.

[197]  Luiz E. Bermudez,et al.  Intracellular Growth in Acanthamoeba castellanii Affects Monocyte Entry Mechanisms and Enhances Virulence of Legionella pneumophila , 1999, Infection and Immunity.

[198]  R. Isberg,et al.  Evidence for pore‐forming ability by Legionella pneumophila , 1998, Molecular microbiology.

[199]  F. Quinn,et al.  Cloning and temperature-dependent expression in Escherichia coli of a Legionella pneumophila gene coding for a genus-common 60-kilodalton antigen , 1989, Infection and immunity.

[200]  A. Jacobs,et al.  The Conjugal Intermediate of Plasmid RSF1010 Inhibits Agrobacterium tumefaciens Virulence and VirB-Dependent Export of VirE2 , 1998, Journal of bacteriology.

[201]  C. Newton,et al.  Growth of Legionella pneumophila in thioglycolate-elicited peritoneal macrophages from A/J mice , 1988, Infection and immunity.

[202]  K. Tamai,et al.  Suppression of apoptosis in mammalian cells by NAIP and a related family of IAP genes , 1996, Nature.

[203]  J. Tommassen,et al.  Antigenic relatedness of a strongly immunogenic 65 kDA mycobacterial protein antigen with a similarly sized ubiquitous bacterial common antigen. , 1988, Microbial pathogenesis.

[204]  M. Swanson,et al.  Co‐ordination of Legionella pneumophila virulence with entry into stationary phase by ppGpp , 1999, Molecular microbiology.

[205]  L. Sibley,et al.  Phagosome acidification blocked by intracellular Toxoplasma gondii , 1985, Nature.

[206]  Rowbotham Tj,et al.  Current views on the relationships between amoebae, legionellae and man. , 1986 .

[207]  F. Ruiz-Cabello,et al.  Secretion by Trypanosoma cruzi of a peptidyl‐prolyl cis‐trans isomerase involved in cell infection. , 1995, The EMBO journal.

[208]  B. Dunn,et al.  Localization of Helicobacter pylori urease and heat shock protein in human gastric biopsies , 1997, Infection and immunity.

[209]  M. S. McClain,et al.  The role of Legionella pneumophila-infected Hartmannella vermiformis as an infectious particle in a murine model of Legionnaire's disease , 1997, Infection and immunity.

[210]  J. Dorca,et al.  Risk factors for nosocomial Legionella pneumophila pneumonia. , 1994, American journal of respiratory and critical care medicine.

[211]  H. Shuman,et al.  The Legionella pneumophila major secretory protein, a protease, is not required for intracellular growth or cell killing , 1990, Infection and immunity.

[212]  J. Hacker,et al.  Mip protein of Legionella pneumophila exhibits peptidyl‐prolyl‐cis/trans isomerase (PPIase) activity , 1992, Molecular microbiology.

[213]  N. Cheville,et al.  Penetration and intracellular growth of Brucella abortus in nonphagocytic cells in vitro , 1990, Infection and immunity.

[214]  V. Yu,et al.  Community-acquired Legionnaires' disease. , 1989, Seminars in respiratory infections.

[215]  T. Meyer,et al.  Pilus genes of Neisseria gonorrheae: chromosomal organization and DNA sequence. , 1984, Proceedings of the National Academy of Sciences of the United States of America.

[216]  M. Horwitz Phagocytosis of the legionnaires' disease bacterium (legionella pneumophila) occurs by a novel mechanism: Engulfment within a Pseudopod coil , 1984, Cell.

[217]  H. Shuman,et al.  The Legionella pneumophila icm locus: a set of genes required for intracellular multiplication in human macrophages , 1994, Molecular microbiology.

[218]  F. Rodgers,et al.  Opsonin-independent adherence and intracellular development of Legionella pneumophila within U-937 cells. , 1993, Canadian journal of microbiology.

[219]  R. Isberg,et al.  Legionnaires' disease: the pore macrophage and the legion of terror within , 1998 .

[220]  J. Songer,et al.  Bacterial phospholipases and their role in virulence. , 1997, Trends in microbiology.

[221]  R. Isberg,et al.  Altered intracellular targeting properties associated with mutations in the Legionella pneumophila dotA gene , 1994, Molecular microbiology.

[222]  H. Shuman,et al.  The Legionella pneumophila rpoS Gene Is Required for Growth within Acanthamoeba castellanii , 1999, Journal of bacteriology.

[223]  M. Swanson,et al.  Expression of Legionella pneumophilaVirulence Traits in Response to Growth Conditions , 1998, Infection and Immunity.

[224]  R. Isberg,et al.  Topology of Legionella pneumophila DotA: an inner membrane protein required for replication in macrophages , 1997, Infection and immunity.

[225]  M. Horwitz,et al.  Identification of a Legionella pneumophila locus required for intracellular multiplication in human macrophages. , 1992, Proceedings of the National Academy of Sciences of the United States of America.

[226]  L. Tompkins,et al.  Analysis of a cloned sequence of Legionella pneumophila encoding a 38 kD metalloprotease possessing haemolytic and cytotoxic activities , 1989, Molecular microbiology.

[227]  J. Hacker,et al.  Influence of site specifically altered Mip proteins on intracellular survival of Legionella pneumophila in eukaryotic cells , 1995, Infection and immunity.

[228]  S. Falkow,et al.  Discovery of virulence genes of Legionella pneumophila by using signature tagged mutagenesis in a guinea pig pneumonia model. , 1999, Proceedings of the National Academy of Sciences of the United States of America.

[229]  N. Cianciotto,et al.  DNA sequence of mip, a Legionella pneumophila gene associated with macrophage infectivity , 1989, Infection and immunity.

[230]  M. Desjardins,et al.  Inhibition of Phagolysosomal Biogenesis by the Leishmania Lipophosphoglycan , 1997, The Journal of experimental medicine.

[231]  J. Barbaree,et al.  Comparison of guinea pig and protozoan models for determining virulence of Legionella species , 1986, Infection and immunity.

[232]  R. Dahl,et al.  Evidence that vesicles containing living, virulent Mycobacterium tuberculosis or Mycobacterium avium in cultured human macrophages are not acidic , 1991, Infection and immunity.

[233]  S. Katz,et al.  Electron microscopic examination of the inflammatory response to Legionella pneumophila in guinea pigs. , 1982, Laboratory investigation; a journal of technical methods and pathology.

[234]  P. D'Arcy Hart,et al.  Ammonia inhibits phagosome–lysosome fusion in macrophages , 1980, Nature.

[235]  W. W. Rhodes,et al.  Pontiac fever. An epidemic of unknown etiology in a health department: I. Clinical and epidemiologic aspects. , 1978, American journal of epidemiology.

[236]  J. Russo,et al.  Relationships between a new type IV secretion system and the icm/dot virulence system of Legionella pneumophila , 1999, Molecular microbiology.

[237]  H. Shuman,et al.  The Legionella pneumophila icmGCDJBFGenes Are Required for Killing of Human Macrophages , 1998, Infection and Immunity.