[Legionella pneumonia in a patient with positive culture results of Legionella pneumophila serotype 1 from bronchoalveolar lavage fluid but negative urinary antigen test results]

A 39-year-old man presented to a local physician complaining of fever, headache without cough or sputum. Abnormal shadows were found on chest X-ray films. Pneumonia was diagnosed and he was referred to our hospital, where chest computed tomography showed bilateral, multifocal, and patchy ground-glass opacities. Neither the urinary antigen test for Streptococcus pneumoniae nor that for Legionella was positive. Because he had visited a public spa several days before developing the fever and headache, and because hypophosphatemia was identified, we then suspected Legionella pneumonia. Bronchoalveolar lavage fluid yielded positive culture of Legionella pneumophila serotype 1. The Legionella urinary antigen is known to detect Legionella pneumophila serotype 1 infection; however, sensitivity and specificity of the test are 60-95% and > 99%, but care should be taken when urinary antigen test results are negative in suspected cases of Legionella pneumophila serotype 1 pneumonia. In the present case, bronchoalveolar lavage fluid was a useful method for diagnosing Legionella pneumonia.

Multifaceted effects of synthetic TLR2 ligand and Legionella pneumophilia on Treg-mediated suppression of T cell activation

BACKGROUND

Regulatory T cells (Treg) play a crucial role in maintaining immune homeostasis and self-tolerance. The immune suppressive effects of Tregs should however be limited in case effective immunity is required against pathogens or cancer cells. We previously found that the Toll-like receptor 2 (TLR2) agonist, Pam3CysSK4, directly stimulated Tregs to expand and temporarily abrogate their suppressive capabilities. In this study, we evaluate the effect of Pam3CysSK4 and Legionella pneumophila, a natural TLR2 containing infectious agent, on effector T (Teff) cells and dendritic cells (DCs) individually and in co-cultures with Tregs.

RESULTS

TLR2 agonists can directly provide a co-stimulatory signal inducing enhanced proliferation and cytokine production of naive CD4+ Teff cells. With respect to cytokine production, DCs appear to be most sensitive to low amounts of TLR agonists. Using wild type and TLR2-deficient cells in Treg suppression assays, we accordingly show that all cells (e.g. Treg, Teff cells and DCs) contributed to overcome Treg-mediated suppression of Teff cell proliferation. Furthermore, while TLR2-stimulated Tregs readily lost their ability to suppress Teff cell proliferation, cytokine production by Teff cells was still suppressed. Similar results were obtained upon stimulation with TLR2 ligand containing bacteria, Legionella pneumophila.

CONCLUSIONS

These findings indicate that both synthetic and natural TLR2 agonists affect DCs, Teff cells and Treg directly, resulting in multi-modal modulation of Treg-mediated suppression of Teff cells. Moreover, Treg-mediated suppression of Teff cell proliferation is functionally distinct from suppression of cytokine secretion.

Secreted bacterial effectors that inhibit host protein synthesis are critical for induction of the innate immune response to virulent Legionella pneumophila

The intracellular bacterial pathogen Legionella pneumophila causes an inflammatory pneumonia called Legionnaires' Disease. For virulence, L. pneumophila requires a Dot/Icm type IV secretion system that translocates bacterial effectors to the host cytosol. L. pneumophila lacking the Dot/Icm system is recognized by Toll-like receptors (TLRs), leading to a canonical NF-κB-dependent transcriptional response. In addition, L. pneumophila expressing a functional Dot/Icm system potently induces unique transcriptional targets, including proinflammatory genes such as Il23a and Csf2. Here we demonstrate that this Dot/Icm-dependent response, which we term the effector-triggered response (ETR), requires five translocated bacterial effectors that inhibit host protein synthesis. Upon infection of macrophages with virulent L. pneumophila, these five effectors caused a global decrease in host translation, thereby preventing synthesis of IκB, an inhibitor of the NF-κB transcription factor. Thus, macrophages infected with wildtype L. pneumophila exhibited prolonged activation of NF-κB, which was associated with transcription of ETR target genes such as Il23a and Csf2. L. pneumophila mutants lacking the five effectors still activated TLRs and NF-κB, but because the mutants permitted normal IκB synthesis, NF-κB activation was more transient and was not sufficient to fully induce the ETR. L. pneumophila mutants expressing enzymatically inactive effectors were also unable to fully induce the ETR, whereas multiple compounds or bacterial toxins that inhibit host protein synthesis via distinct mechanisms recapitulated the ETR when administered with TLR ligands. Previous studies have demonstrated that the host response to bacterial infection is induced primarily by specific microbial molecules that activate TLRs or cytosolic pattern recognition receptors. Our results add to this model by providing a striking illustration of how the host immune response to a virulent pathogen can also be shaped by pathogen-encoded activities, such as inhibition of host protein synthesis.

[Comparison and evaluation of the Binax EIA and Biotest EIA urinary antigen kits for detection of Legionella pneumophila antigen in urine samples]

The Binax and the Biotest urinary antigen kits for detection of L. pneumophila antigen were compared by testing of selected 67 urine samples obtained from EWGLI as reference samples in External Quality Assessment Scheme. Thirty nine were positive with the Binax kit (100% of sensitivity), and 33 were positive with the Biotest (84.6% of sensitivity). The test specificities were 100% for the both kits. It was concluded that the Binax kit was more suitable for the routine diagnosis of Legionella infections than the Biotest kit.

Isolation and identification of Legionella pneumophila from material reclamation facilities

Sampling points at a material reclamation facility (MRF) were monitored over three months for the presence of Legionella spp. A number of different Legionellae were isolated and typed to identify L. pneumophila serogroup 1, the serotype which is the most common human pathogen. Phenotypic methods resulted in a total of 61 presumptive isolates of Legionella spp. Using latex agglutination, 26 out of the 61 were identified as L. pneumophila serogroup 1, 23 as L. pneumophila serogroups 2-14, and the remaining 12 were Legionella spp. However, on typing using pulse field gel electrophoresis, the 26 L. pneumophila serotype 1 isolates were a diverse group of 25 PFGE types with none persisting in the environment over time. This diversity suggests that there are a number of contamination sources for this important human pathogen in the MRF environment which constitute a risk to health for operatives in these facilities.

Sero diagnosis of Legionella infection in community acquired pneumonia

BACKGROUND & OBJECTIVES

Legionella pneumophila has been increasingly recognized as an emerging pathogen responsible for community acquired pneumonia (CAP) worldwide. In India, the actual burden is not known. The present study was thus undertaken to see the presence of Legionella infection in patients with community acquired pneumonia admitted in a tertiary care centre in north India.

METHODS

Both children and adults (n=113) with symptoms of pneumonia were included in the study. Clinical samples (blood, urine, nasopharyngeal aspirates, bronchoalveolar lavage, sputum, etc.) were collected and subjected to culture and other tests. Enzyme linked immunosorbent assay (ELISA) was done by commercial kits for all the three classes of immunoglobulins (IgG, IgM & IgA). Urinary antigen was also detected using commercial kits. Culture was performed on 51 respiratory tract fluid samples. Serum samples of 44 healthy controls were also screened for the presence of anti-legionella antibodies (IgG, IgM & IgA).

RESULTS

Thirty one of the 113 cases (27.43%) were serologically positive. Anti-legionella IgG, IgM and IgA antibodies were positive in 7.96, 15.92 and 11.50 per cent patients respectively. In controls, seropositivity was 9.09 (4/44). IgA was positive in 3 and IgM, IgG combined in one. Antigenuria detection by Microwell ELISA kit showed 17.69 per cent positivity. Four antigenuria positive patients were also serologically positive; of these two patients were positive for IgM, hence considered as confirmed cases of Legionella infection. None of the sample was culture positive.

INTERPRETATION & CONCLUSIONS

Combination of serology and antigenuria detection may be a valuable tool for the diagnosis of Legionella infection in absence of culture positivity. In order to evaluate the actual burden of Legionella in community acquired pneumonia, further studies with larger samples need to be done.

Rapid diagnostic testing for community-acquired pneumonia: can innovative technology for clinical microbiology be exploited?

Two nonsynchronous events have affected the management of community-acquired pneumonia (CAP): spiraling empiricism for CAP and the "golden era" of clinical microbiology. The development of broad-spectrum antibiotics has led to widespread empiric use without ascertaining the etiology of the infecting microbe. Unfortunately, this approach clashes with the second event, which is the advent of molecular-based microbiology that can identify the causative pathogen rapidly at the point of care. The urinary antigen is a most effective rapid test that has allowed targeted therapy for Legionnaire disease at the point of care. The high specificity (> 90%) allows the clinician to administer appropriate anti-Legionella therapy based on a single rapid test; however, its low sensitivity (76%) means that a notable number of cases of Legionnaire disease will go undiagnosed if other tests, especially culture, are not performed. Further, culture for Legionella is not readily available. If a culture is not performed, epidemiologic identification of the source of the bacterium cannot be ascertained by molecular fingerprinting of the patient and the putative source strain. We recommend resurrection of the basic principles of infectious disease, which are to identify the microbial etiology of the infection and to use narrow, targeted antimicrobial therapy. To reduce antimicrobial overuse with subsequent antimicrobial resistance, these basic principles must be applied in concert with traditional and newer tests in the clinical microbiology laboratory.

Caspase-7 activation by the Nlrc4/Ipaf inflammasome restricts Legionella pneumophila infection

Legionella pneumophila (L. pneumophila), the causative agent of a severe form of pneumonia called Legionnaires' disease, replicates in human monocytes and macrophages. Most inbred mouse strains are restrictive to L. pneumophila infection except for the A/J, Nlrc4^−/− (Ipaf^−/−), and caspase-1^−/− derived macrophages. Particularly, caspase-1 activation is detected during L. pneumophila infection of murine macrophages while absent in human cells. Recent in vitro experiments demonstrate that caspase-7 is cleaved by caspase-1. However, the biological role for caspase-7 activation downstream of caspase-1 is not known. Furthermore, whether this reaction is pertinent to the apoptosis or to the inflammation pathway or whether it mediates a yet unidentified effect is unclear. Using the intracellular pathogen L. pneumophila, we show that, upon infection of murine macrophages, caspase-7 was activated downstream of the Nlrc4 inflammasome and required caspase-1 activation. Such activation of caspase-7 was mediated by flagellin and required a functional Naip5. Remarkably, mice lacking caspase-7 and its macrophages allowed substantial L. pneumophila replication. Permissiveness of caspase-7^−/− macrophages to the intracellular pathogen was due to defective delivery of the organism to the lysosome and to delayed cell death during early stages of infection. These results reveal a new mechanism for caspase-7 activation downstream of the Nlrc4 inflammasome and present a novel biological role for caspase-7 in host defense against an intracellular bacterium.

Legionella pneumophila causes a severe form of pneumonia called Legionnaires' disease. In human macrophages, L. pneumophila establishes special vacuoles that do not fuse with the lysosome and grows intracellularly. However, in mouse macrophages, the bacteria are efficiently delivered to the lysosome for degradation. Importantly, caspase-1 is activated when L. pneumophila infects mouse macrophages, but not when it infects human cells. Caspase-1 activation promotes the fusion of the L. pneumophila vacuole with the lysosome and macrophage death. However, the caspase-1 substrate mediating such effects is unknown. Experiments performed in vitro demonstrate that caspase-7 is a substrate of caspase-1. Yet, it is not known if the reaction takes place within the macrophage, and it is unclear if it has any biological effect. In this study we show that, in mouse macrophages, caspase-7 is activated by L. pneumophila downstream of caspase-1 and requires the host receptors Nlrc4 and Naip5. Remarkably, caspase-7 activation during L. pneumophila infection restricts growth by promoting early macrophage death and efficient delivery of the organism to the lysosome. Consequently, L. pneumophila grows in the macrophages and the lungs of caspase-7^−/− mice. Therefore, we demonstrate a novel caspase-7 activation pathway that contributes to the restriction of L. pneumophila infection.

Seroepidemiological study after a long-distance industrial outbreak of legionnaires' disease

Following a long-distance outbreak of Legionnaires' disease from an industrial air scrubber in Norway in 2005, a seroepidemiological study measuring levels of immunoglobulin G (IgG) and IgM antibodies to Legionella pneumophila was performed with a polyvalent enzyme-linked immunosorbent assay. One year after the outbreak, IgG levels in employees (n = 213) at the industrial plant harboring the scrubber and in blood donors (n = 398) from the outbreak county were low but significantly higher (P < or = 0.002) than those in blood donors (n = 406) from a nonexposed county. No differences in IgM levels among the three groups were found after adjustment for gender and age. Home addresses of the seroresponders in the exposed county clustered to the city of the outbreak, in contrast to the scattering of addresses of the seroresponding donors in the nonexposed county. Factory employees who operated at an open biological treatment plant had significantly higher IgG and IgM levels (P < or = 0.034) than those working >200 m away. Most of the healthy seroresponders among the factory employees worked near this exposure source. Immunoblotting showed that IgG and IgM antibodies in 82.1% of all seroresponders were directed to the lipopolysaccharide of the L. pneumophila serogroup 1 outbreak strain. In conclusion, 1 year after the long-distance industrial outbreak a small increase in IgG levels of the exposed population was observed. The open biological treatment plant within the industrial premises, however, constituted a short-distance exposure source of L. pneumophila for factory employees working nearby.

[Inspection on Legionella pollution and the health impact of workers in public places of central air conditioning systems in Dalian City]

OBJECTIVE

To inspect the conditions of Legionella pollution in cooling towers of central air conditioning systems and the state of Legionella potential infection of workers in public places in Dalian City in order to study the impact factors related witb Legiondlla organism infection.

METHODS

From August to September 2005, water sample of 32 cooling towers were randomly collected. Legionella organism in water samples were detected. The blood samples were randomly collected from workers in public places of central air conditioning systems. The micro agglutination test was used for detecting the Legionella antibodies in blood samples.

RESULTS

53.13% of the cooling towers were positive with Legionella pneumophila (Up) serogroup 7, 8, 9 and 10, of which, Lp9 isolates were predominant by 77.78% (N=28). The testing results of Legionella 'antibodies showed that the antibody levels of Legionella were the highest. The results implied there were potential infection of workers in public places of central air conditioning systems.

CONCLUSION

Legionella pollution exist in cooling towers and the Legionella potential infection were found in workers in public places of central air conditioning systems in Dalian City.

Type IV secretion-dependent activation of host MAP kinases induces an increased proinflammatory cytokine response to Legionella pneumophila

The immune system must discriminate between pathogenic and nonpathogenic microbes in order to initiate an appropriate response. Toll-like receptors (TLRs) detect microbial components common to both pathogenic and nonpathogenic bacteria, whereas Nod-like receptors (NLRs) sense microbial components introduced into the host cytosol by the specialized secretion systems or pore-forming toxins of bacterial pathogens. The host signaling pathways that respond to bacterial secretion systems remain poorly understood. Infection with the pathogen Legionella pneumophila, which utilizes a type IV secretion system (T4SS), induced an increased proinflammatory cytokine response compared to avirulent bacteria in which the T4SS was inactivated. This enhanced response involved NF-κB activation by TLR signaling as well as Nod1 and Nod2 detection of type IV secretion. Furthermore, a TLR- and RIP2-independent pathway leading to p38 and SAPK/JNK MAPK activation was found to play an equally important role in the host response to virulent L. pneumophila. Activation of this MAPK pathway was T4SS-dependent and coordinated with TLR signaling to mount a robust proinflammatory cytokine response to virulent L. pneumophila. These findings define a previously uncharacterized host response to bacterial type IV secretion that activates MAPK signaling and demonstrate that coincident detection of multiple bacterial components enables immune discrimination between virulent and avirulent bacteria.

The host immune system senses bacterial infection by recognizing conserved bacterial components. The host can differentiate between virulent and avirulent bacteria by detecting the activity of bacterial secretion systems that inject effector proteins into cells. How the host responds to such bacterial secretion systems is not fully understood. Using the bacterial pathogen Legionella pneumophila and isogenic mutants that differ in defined virulence properties, a robust immune response to L. pneumophila and its type IV secretion system was identified. Using macrophages lacking various aspects of the innate immune system, it was found that this host response is comprised of signaling by extracellular and intracellular immune receptors, as well as host signaling triggered by the type IV secretion system. Through genomic and biochemical analyses of L. pneumophila–infected macrophages, type IV secretion was found to activate additional host signaling pathways distinct from known immune pathways. Our data indicate that coincident detection of multiple bacterial components is required for a robust immune response to bacterial infection and highlights a key host pathway triggered by bacterial type IV secretion that contributes to this immune response.

Non-opsonic phagocytosis of Legionella pneumophila by macrophages is mediated by phosphatidylinositol 3-kinase

Background

Legionella pneumophila, is an intracellular pathogen that causes Legionnaires' disease in humans, a potentially lethal pneumonia. L. pneumophila has the ability to enter and replicate in the host and is essential for pathogenesis.

Methodology/Principal Findings

Phagocytosis was measured by cell invasion assays. Construction of PI3K mutant by PCR cloning and expression of dominant negative mutant was detected by Western blot. PI3K activity was measured by ³²P labeling and detection of phospholipids products by thin layer chromatography. Infection of macrophages with virulent L. pneumophila stimulated the formation of phosphatidylinositol 3-phosphate (PIP3), a phosphorylated lipid product of PI3K whereas two structurally distinct phosphatidylinositol 3 kinase (PI3K) inhibitors, wortmannin and LY294002, reduced L. pneumophila entry into macrophages in a dose-dependent fashion. Furthermore, PI3K activation led to Akt stimulation, a serine/threonine kinase, which was also inhibited by wortmannin and LY294002. In contrast, PI3K and protein kinase B (PKB/Akt) activities were lower in macrophages infected with an avirulent bacterial strain. Only virulent L. pneumophila increased lipid kinase activity present in immunoprecipitates of the p85α subunit of class I PI3K and tyrosine phosphorylated proteins. In addition, macrophages expressing a specific dominant negative mutant of PI3K reduced L. pneumophila entry into these cells.

Conclusion/Significance

Entry of L. pneumophila is mediated by PI3K/Akt signaling pathway. These results suggest an important role for PI3K and Akt in the L. pneumophila infection process. They point to possible novel strategies for undermining L. pneumophila host uptake and reducing pathogenesis of Legionnaires' disease.

[Experience of microbiologic diagnostics of acute pneumonia cases arose in town Verkhnyaya Pyshma in July-August 2007]

Bacteriologic, serologic, and PCR tests of blood, sputum, serum and autopsy samples from 91 patients were performed during outbreak of pneumonia in town Verkhnyaya Pyshma in July-August 2007. Streptococcus pneumoniae was isolated from 20% of diagnostically meaningful samples of sputum and from 50% of autopsy samples. Diagnosis of Legionnaires' disease was confirmed in 48% of cases. It was shown that association of Streptococcus pneumoniae and Legionella pneumophila determined the affect during such pneumonia. Need for establishment of diagnostic procedure for patients with pneumonia including those caused by atypical agents was revealed.

[Standards for laboratory diagnostics of legionellosis and their application during epidemic outbreak of pneumonia in town Verkhnyaya Pyshma]

High effectiveness of application of international standards for legionellosis laboratory diagnostics was confirmed during investigation of pneumonia outbreak in town Verkhnyaya Pyshma. Use of immunochromatographic method and enzyme immunoassay for detection of Legionella antigen in urine of patients allows to confirm diagnosis of Legionella infection during several hours, promptly begin etiologic antibacterial treatment and reveal possible sources of infection in potentially dangerous environmental objects.

Clinical features of two cases of Legionnaires' disease with persistence of Legionella urinary antigen excretion

The advantages of diagnosing legionellosis by urinary antigen detection are widely recognized, and include early detection, rapidity of testing, and ease of specimen collection. However, the persistence of Legionella urinary antigen excretion has been suggested in some selected patients, although the clinical features of these patients have not yet been clearly described. Here, we describe the clinical features of two patients with Legionnaires' disease with persistence of Legionella urinary antigen excretion (117 days and 247 days). One patient had an underlying disease, adult T-cell leukemia, and the other patient had ulcerative colitis and was receiving oral corticosteroids. Unusual clinical and radiological findings as well as a review of the literature are presented.

Mechanisms of Legionella pneumophila-induced interleukin-8 expression in human lung epithelial cells

BACKGROUND

Legionella pneumophila is a facultative intracellular bacterium, capable of replicating within the phagosomes of macrophages and monocytes, but little is known about its interaction with human lung epithelial cells. We investigated the effect of L. pneumophila on the expression of interleukin-8 (IL-8) in human A549 alveolar and NCI-H292 tracheal epithelial cell lines.

RESULTS

Infection of L. pneumophila strain, but not heat-killed strain, resulted in upregulation of IL-8. IL-8 mRNA expression was induced immediately after the infection and its signal became gradually stronger until 24 h after infection. On the other hand, IL-8 expression in A549 cells infected with L. pneumophila lacking a functional type IV secretion system was transient. The IL-8 expression was slightly induced at 16 h and increased at 24 h after infection with flagellin-deficient Legionella. Activation of the IL-8 promoter by L. pneumophila infection occurred through the action of nuclear factor-kappaB (NF-kappaB). Transfection of dominant negative mutants of NF-kappaB-inducing kinase, IkappaB kinase and IkappaB inhibited L. pneumophila-mediated activation of IL-8 promoter. Treatment with hsp90 inhibitor suppressed L. pneumophila-induced IL-8 mRNA due to deactivation of NF-kappaB.

CONCLUSION

Collectively, these results suggest that L. pneumophila induces activation of NF-kappaB through an intracellular signaling pathway that involves NF-kappaB-inducing kinase and IkappaB kinase, leading to IL-8 gene transcription, and that hsp90 acts as a crucial regulator in L. pneumophila-induced IL-8 expression, presumably contributing to immune response in L. pneumophila. The presence of flagellin and a type IV secretion system are critical for Legionella to induce IL-8 expression in lung epithelial cells.

Immune-like phagocyte activity in the social amoeba

Social amoebae feed on bacteria in the soil but aggregate when starved to form a migrating slug. We describe a previously unknown cell type in the social amoeba, which appears to provide detoxification and immune-like functions and which we term sentinel (S) cells. S cells were observed to engulf bacteria and sequester toxins while circulating within the slug, eventually being sloughed off. A Toll/interleukin-1 receptor (TIR) domain protein, TirA, was also required for some S cell functions and for vegetative amoebae to feed on live bacteria. This apparent innate immune function in social amoebae, and the use of TirA for bacterial feeding, suggest an ancient cellular foraging mechanism that may have been adapted to defense functions well before the diversification of the animals.

Increased sensitivity of a direct fluorescent antibody test for Legionella pneumophila in bronchoalveolar lavage samples by immunomagnetic separation based on BioMags

In the present study, immunomagnetic separation of Legionella pneumophila from mock bronchoalveolar lavage (BAL) fluid samples, which were artificially spiked with L. pneumophila, and culture positive patient BAL fluid samples, was achieved using BioMags (superparamagnetic particles) loaded with purified rabbit immunoglobulin G specific for L. pneumophila. Bacteria binding onto BioMag-immunomatrix were directly stained with a L. pneumophila species-specific DFA reagent and examined under a fluorescence microscope. BioMag-based immunomagnetic separation (BIMS) followed by DFA staining (BIMS-DFA) could correctly identify all the 20 (100%) BAL samples which were spiked with low numbers (2x10(2) CFU) of L. pneumophila. Cultures could be recovered from 15 (75%) of these 20 spiked BAL samples, 5 (25%) of the samples failed to yield positive cultures. Both culture and BIMS-DFA methods showed 100% positive results when spiked BAL samples containing high bacterial load (10(4) CFU) were tested. The findings with true patient culture positive BAL specimens which were examined retrospectively indicated that BIMS-DFA is significantly more sensitive for detecting L. pneumophila than conventional cytospin method of DFA staining (cytospin-DFA). Out of the 25 culture positive BAL specimens tested, 7 (28%) proved negative by cytospin-DFA whereas BIMS-DFA correctly detected all the 25 (100%) specimens. It is suggested that the BIMS-DFA procedure increases the sensitivity of DFA testing for L. pneumophila in large volume samples such as BAL fluids.