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Query: UMLS:C0023241 (Legionella)
 6,990 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Several bacterial pathogens utilize conjugation machines to export effector molecules during infection. Such systems are members of the type IV or 'adapted conjugation' secretion family. The prototypical type IV system is the Agrobacterium tumefaciens T-DNA transfer machine, which delivers oncogenic nucleoprotein particles to plant cells. Other pathogens, including Bordetella pertussis, Legionella pneumophila, Brucellaspp. and Helicobacter pylori, use type IV machines to export effector proteins to the extracellular milieu or the mammalian cell cytosol.
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PMID:Bacterial type IV secretion: conjugation systems adapted to deliver effector molecules to host cells. 1092 Mar 94

Concern about emerging and reemerging respiratory pathogens prompted the development of a respiratory disease reference laboratory at the Naval Health Research Center. Professionals working in this laboratory have instituted population-based surveillance for pathogens that affect military trainees and responded to threats of increased respiratory disease among high-risk military groups. Capabilities of this laboratory that are unique within the Department of Defense include adenovirus testing by viral shell culture and microneutralization serotyping, influenza culture and hemagglutination inhibition serotyping, and other special testing for Streptococcus pneumoniae, Streptococcus pyogenes, Mycoplasma pneumonia, and Chlamydia pneumoniae. Projected capabilities of this laboratory include more advanced testing for these pathogens and testing for other emerging pathogens, including Bordetella pertussis, Legionella pneumoniae, and Haemophilus influenzae type B. Such capabilities make the laboratory a valuable resource for military public health.
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PMID:The Naval Health Research Center Respiratory Disease Laboratory. 1092 Jun 35

"Atypical pneumonia" is a term loosely applied to lower respiratory tract infections that are not characterized by signs and symptoms of lobar consolidation. This description can apply to disease caused by a variety of bacterial, viral and even protozoan organisms. In reality, differentiation as to etiology of pneumonia cannot be distinguished on the basis of clinical presentation. This review will discuss the epidemiology, clinical manifestations, and laboratory diagnosis of Mycoplasma pneumoniae, Chlamydia sp., Legionella sp., Bordetella pertussis, and Coxiella bumetii, the most common agents associated with atypical pneumonia. Unfortunately, because many of these pathogens are intracellular, culture systems are either not available or the techniques employed are costly, time-consuming or unsafe. Until molecular techniques are standardized and widely available, diagnosis will depend upon serologic confirmation. Given the relative importance of these organisms as causes of community acquired pneumonia, current practice guidelines recommend empiric therapy with a macrolide in patients well enough to be treated as an outpatient. However, diagnostic tests should be performed in any patient requiring hospitalization.
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PMID:Laboratory diagnosis of atypical pneumonia. 1098 28

Bacterial conjugation systems are highly promiscuous macromolecular transfer systems that impact human health significantly. In clinical settings, conjugation is exceptionally problematic, leading to the rapid dissemination of antibiotic resistance genes and other virulence traits among bacterial populations. Recent work has shown that several pathogens of plants and mammals - Agrobacterium tumefaciens, Bordetella pertussis, Helicobacter pylori and Legionella pneumophila - have evolved secretion pathways ancestrally related to conjugation systems for the purpose of delivering effector molecules to eukaryotic target cells. Each of these systems exports distinct DNA or protein substrates to effect a myriad of changes in host cell physiology during infection. Collectively, secretion pathways ancestrally related to bacterial conjugation systems are now referred to as the type IV secretion family. The list of putative type IV family members is increasing rapidly, suggesting that macromolecular transfer by these systems is a widespread phenomenon in nature.
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PMID:Type IV secretion: intercellular transfer of macromolecules by systems ancestrally related to conjugation machines. 1130 13

Type IV secretion systems (TFSS) mediate secretion or direct cell-to-cell transfer of virulence factors (proteins or protein-DNA complexes) from many Gram-negative animal, human and plant pathogens, such as Agrobacterium tumefaciens, Bartonella tribocorum, Bordetella pertussis, Brucella suis, Helicobacter pylori, Legionella pneumophila and Rickettsia prowazekii, into eukaryotic cells. Bacterial conjugation is also classified as a TFSS-like process mediating the spread of broad-host-range plasmids between Gram-negative bacteria such as RP4 and R388, which carry antibiotic resistance genes. Genetic, biochemical, cell biological and structural biology experiments led to significant progress in the understanding of several aspects of TFSS processes. X-ray crystallography revealed that homologues of the A. tumefaciens inner membrane-associated proteins VirB11 and VirD4 from H. pylori and R388, respectively, may form channels for substrate translocation or assembly of the transmembrane TFSS machinery. Biochemical and cell biological experiments revealed interactions between components of the periplasmic core components VirB8, VirB9 and VirB10, which may form the translocation channel. Analysis of A. tumefaciens virulence proteins VirE2 and VirF suggested that the periplasmic translocation route of the pertussis toxin from B. pertussis may be more generally valid than previously anticipated. Secretion and modification of toxins from H. pylori and L. pneumophila profoundly affect host cell metabolism, thus entering the discipline of cellular microbiology. Finally, results from genome sequencing projects revealed the presence of up to three TFSS in a single organism, and the analysis of their interplay and adaptation to different functions will be a future challenge. TFSS-carrying plasmids were discovered in different ecosystems, suggesting that genetic exchange may speed up their evolution and adaptation to different cell-cell interactions.
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PMID:Bacterial secrets of secretion: EuroConference on the biology of type IV secretion processes. 1191 19

Lipopolysaccharide (LPS) derived from enterobacteria elicit in several cell types cellular responses that are restricted in the use of Toll-like receptor 4 (TLR4) as the principal signal-transducing molecule. A tendency to consider enterobacterial LPS as a prototypic LPS led some authors to present this mechanism as a paradigm accounting for all LPSs in all cell types. However, the structural diversity of LPS does not allow such a general statement. By using LPSs from bacteria that do not belong to the Enterobacteriaceae, we show that in bone marrow cells (BMCs) the LPS of Rhizobium species Sin-1 and of three strains of Legionella pneumophila require TLR2 rather than TLR4 to elicit the expression of CD14. In addition, exposure of BMCs from TLR4-deficient (C3H/HeJ) mice to the lipid A fragment of the Bordetella pertussis LPS inhibits their activation by the Legionella lipid A. The data show selective action of different LPSs via different TLRs, and suggest that TLR2 can interact with many lipid A structures, leading to either agonistic or specific antagonistic effects.
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PMID:Lipopolysaccharides from Legionella and Rhizobium stimulate mouse bone marrow granulocytes via Toll-like receptor 2. 1248 15

Type IV transporters are produced by several bacterial pathogens such as Agrobacterium tumefaciens, Bordetella pertussis, Brucella spp., Bartonella henselae, Helicobacter pylori and Legionella pneumophila. These transporters are critical for the pathogenic process in that they export important virulence factors across the membranes of the bacteria. Although the virulence factors that are exported by these transporters can be either nucleic acid or protein, the general mechanism of transport appears to be similar for members of this family. Recent findings have shed light on the architecture of type IV transporters and the roles that these transporters play in pathogenesis.
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PMID:Type IV transporters of pathogenic bacteria. 1261 16

Type IV secretion systems (T4SSs) are bacterial multiprotein organelles specialised in the transfer of (nucleo)protein complexes across cell membranes. They are essential for conjugation, bacterial-induced tumour formation in plant cells, as observed in Agrobacterium, toxin secretion, like in Bordetella and Helicobacter, cell-to-cell translocation of virulence factors, and intracellular activity of mammalian pathogens like Legionella. By enabling conjugative DNA delivery, these systems contribute to the spread of antibiotic resistance genes among bacteria. These translocons are made up by 10-15 proteins that are analogous to Vir proteins of Agrobacterium and traverse both membranes and the periplasmic space in between in Gram-negative bacteria. Their secretion substrates range from single-stranded DNA/protein complexes to multicomponent toxins and they are assisted by integral inner-membrane coupling factors, the multimeric type-IV coupling proteins (T4CPs), to connect the macromolecular complexes to be transferred with the secretory conduit. To do so, these T4CPs may be required to localise close to the secretion machinery within the donor cell. The T4CP structural prototype is the hexameric protein TrwB of Escherichia coli conjugative plasmid R388, closely related to Agrobacterium VirD4 protein. It is responsible for coupling the relaxosome with the DNA transport apparatus during cell mating. T4CP family members are related to SpoIIIE/FtsK proteins, essential for DNA pumping during sporulation and cell division. These features suggest possible mechanisms for conjugal T4CP function: as a simple coupler between two molecular machines, as a rotating device to pump DNA through the type-IV transport pore, or as a DNA injector, whereby its central channel would function as part of the transport pore.
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PMID:Coupling factors in macromolecular type-IV secretion machineries. 1513 75

The Legionella pneumophila Dot/Icm system is a type IV secretion apparatus that transfers bacterial proteins into eukaryotic host cells. The RalF protein is a substrate engaged and translocated into host cells by the Dot/Icm system. In this study, the mechanism of Dot/Icm-mediated translocation of RalF has been investigated. It was determined that RalF translocation into host cells occurs before bacterial internalization. Sequences essential for RalF translocation were located at the C terminus of the RalF protein. A fusion protein consisting of a 20-aa C-terminal RalF peptide appended to the calmodulin-dependent adenylate cyclase domain of the Bordetella pertussis adenylate cyclase protein was translocated into host cells by the Dot/Icm system. A leucine (L372) residue at the -3 position in relation to the RalF C terminus was critical for translocation. Consistent with RalF L372 playing an important role in substrate recognition by the Dot/Icm system, most other Dot/Icm substrates were found to have amino acid residues with similar physical properties at their -3 or -4 C-terminal positions. These data demonstrate that the Dot/Icm system can transfer bacterial proteins that modulate host cellular functions before uptake and indicate that substrate recognition involves a C-terminal translocation signal. Thus, Legionella has the ability to engage synthesized substrate proteins and transfer them into host cells on contact, enabling Legionella to rapidly alter transport of the vacuole in which it resides.
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PMID:A C-terminal translocation signal required for Dot/Icm-dependent delivery of the Legionella RalF protein to host cells. 1561 86

Respiratory disease caused by atypical bacteria remains an important cause of morbidity and mortality for adults and children, despite the widespread use of effective antimicrobials agents. Culture remains the "gold standard" for the detection of these agents. However, culture is labor-intensive, takes several days to weeks for growth, and can be very insensitive for the detection of some of these organisms. Newer singleplex PCR diagnostic tests are sensitive and specific, but multiple assays would be needed to detect all of the common pathogens. Therefore, we developed the Pneumoplex assays, a multiplex PCR-enzyme hybridization assay (the standard assay) and a multiplex real-time assay to detect the most common atypical pathogens in a single test. Primer and probe sequences were designed from conserved regions of specific genes for each of these organisms. The limits of detection were as follows: for Bordetella pertussis, 2 CFU/ml; for Legionella pneumophila (serotypes 1 to 15) and Legionella micdadei, 9 and 80 CFU/ml, respectively; for Mycoplasma pneumoniae, 5 CFU/ml; and for Chlamydia (Chlamydophila) pneumoniae, 0.01 50% tissue culture infective doses. Recombinant DNA controls for each of these organisms were constructed, and the number of copies for each DNA control was calculated. The Pneumoplex could detect each DNA control down to 10 copies/ml. The analytical specificity demonstrated no cross-reactivity between 23 common respiratory pathogens. One hundred twenty-five clinical bronchoalveolar lavage fluid samples tested by the standard assay demonstrated that the Pneumoplex yielded a sensitivity and a specificity of 100 and 98.5%, respectively. This test has the potential to assist clinicians in establishing a specific etiologic diagnosis before initiating therapy, to decrease hospital costs, and to prevent inappropriate antimicrobial therapy.
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PMID:The pneumoplex assays, a multiplex PCR-enzyme hybridization assay that allows simultaneous detection of five organisms, Mycoplasma pneumoniae, Chlamydia (Chlamydophila) pneumoniae, Legionella pneumophila, Legionella micdadei, and Bordetella pertussis, and its real-time counterpart. 1569 46


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