Cutaneous Legionella infections in allogeneic hematopoietic cell transplantation recipients.

To date, only twenty cases of cutaneous legionellosis have been reported. Cutaneous legionellosis has heterogeneous manifestations including abscesses, nodules, and cellulitis. The detection of most cutaneous Legionella species requires specific diagnostic cultures and assays. Herein, we report a case of cutaneous legionella in a hematopoietic cell transplantation recipient with culture-negative nodules unresponsive to empiric antibiotics. We also discuss the varied morphology of cutaneous legionellosis and important diagnostic considerations.

Legionella longbeachae Is Immunologically Silent and Highly Virulent In Vivo.

BACKGROUND: Legionella longbeachae (Llo) and Legionella pneumophila (Lpn) are the most common pneumonia-causing agents of the genus. Although both species can be lethal to humans and are highly prevalent, little is known about the molecular pathogenesis of Llo infections. In murine models of infection, Lpn infection is self-limited, whereas Llo infection is lethal. METHODS: We used mouse macrophages, human macrophages, human epithelial cells, and mouse infections in vivo to evaluate multiple parameters of the infection. RESULTS: We determined that the Llo Dot/Icm secretion system is critical for virulence. Different than Lpn, Llo disseminates and the animals develop a severe pulmonary failure, as demonstrated by lung mechanics and blood oxygenation assays. As compared to Lpn, Llo is immunologically silent and fails to trigger the production of cytokines in human pulmonary epithelial cells and in mouse and human macrophages. Infections in Tnfr1-/-, Ifng-/-, and Il12p40-/- mice supported the participation of cytokines for the resistance phenotype. CONCLUSIONS: Both Lpn and Llo require the Dot/Icm system for pathogenesis, but the infection outcome is strikingly different. Llo is immunologically silent, highly virulent, and lethal. The differences reported herein may reflect unappreciated clinical differences in patients infected with Lpn or Llo.

Comparative analysis of virulence traits between a Legionella feeleii strain implicated in Pontiac fever and a strain that caused Legionnaires' disease.

Legionella strains of the same species and serogroup are known to cause Legionnaires' disease (a potentially fatal atypical pneumonia) or Pontiac fever (a mild, flu-like disease), but the bacterial factors that define these dramatic differences in pathology have not been elucidated. To gain a better understanding of these factors, we compared the characteristics of Legionella feeleii strains that were isolated from either a sample of freshwater implicated in an outbreak of Pontiac fever (ATCC 35072, serogroup 1, LfPF), or a patient with Legionnaires' disease (ATCC 38549, serogroup 2, LfLD). Growth of LfPF and LfLD in BYE broth was slower than the positive control, Legionella pneumophila strain JR32. However, LfLD grew faster than LfPF at 42 °C. After in vitro infection to J774 murine or U937 human macrophage cell lines and A549 human lung epithelial cell line, LfLD showed a higher cell infection rate, stronger internalization by host cells, and greater cytotoxicity than that of LfPF. Large amounts of IL-6 and IL-8 were secreted by human host cells after infection with LfLD, but not with LfPF. LfLD possessed mono-polar flagellum while LfPF was unflagellated. When LfLD was cultured at 25, 30 and 37 °C, the bacteria had higher motility rate at lower temperatures. Based on our results, this is the first study that showed distinct characteristics between LfPF and LfLD, which may give important leads in elucidating differences in their virulence.

Microbiological and Clinical Studies of Legionellosis in 33 Patients with Cancer.

Legionella, a large group of environmental Gram-negative bacteria, represents an occasional cause of pneumonia. We analyzed the microbiological and clinical features of 33 consecutive cases of Legionella infections that occurred at the University of Texas MD Anderson Cancer Center, Houston, TX, from 2002 to 2014. The Legionella strains were isolated from bronchoscopy specimens (32 strains) and a blood culture (1 strain) and were identified by sequencing analysis of the full-length 16S rRNA gene. The 33 strains involved 12 Legionella species or subspecies: 15 strains of L. pneumophila subsp. pneumophila, 3 strains of L. pneumophila subsp. fraseri or L. pneumophila subsp. pascullei, 4 strains of "L. donaldsonii," 3 strains of L. micdadei, and one each of L. bozemanae, L. feeleii, L. gormanii, L. longbeachae, L. maceachernii, L. parisiensis, L. sainthelensi, and Legionella sp. strain D5382. All patients except one asymptomatic carrier showed pneumonia, including one with concurrent bacteremia. Nine patients died, with this infection being the immediate cause of death in six. Twenty-seven patients had underlying hematologic malignancies. Twenty-three patients were leukopenic. Six patients were recipients of allogeneic hematopoietic stem cell transplant, with their infections caused by five Legionella species. Together, these results suggest that diverse Legionella species infect patients with cancer in the Houston area and its vicinity. The five cases of pneumonia due to L. donaldsonii and Legionella sp. D5382 are likely the first reports of human infection with these organisms.

Different STAT Transcription Complexes Drive Early and Delayed Responses to Type I IFNs.

IFNs, which transduce pivotal signals through Stat1 and Stat2, effectively suppress the replication of Legionella pneumophila in primary murine macrophages. Although the ability of IFN-γ to impede L. pneumophila growth is fully dependent on Stat1, IFN-αß unexpectedly suppresses L. pneumophila growth in both Stat1- and Stat2-deficient macrophages. New studies demonstrating that the robust response to IFN-αß is lost in Stat1-Stat2 double-knockout macrophages suggest that Stat1 and Stat2 are functionally redundant in their ability to direct an innate response toward L. pneumophila. Because the ability of IFN-αß to signal through Stat1-dependent complexes (i.e., Stat1-Stat1 and Stat1-Stat2 dimers) has been well characterized, the current studies focus on how Stat2 is able to direct a potent response to IFN-αß in the absence of Stat1. These studies reveal that IFN-αß is able to drive the formation of a Stat2 and IFN regulatory factor 9 complex that drives the expression of a subset of IFN-stimulated genes, but with substantially delayed kinetics. These observations raise the possibility that this pathway evolved in response to microbes that have devised strategies to subvert Stat1-dependent responses.

An update on iron acquisition by Legionella pneumophila: new pathways for siderophore uptake and ferric iron reduction.

Iron acquisition is critical for the growth and pathogenesis of Legionella pneumophila, the causative agent of Legionnaires' disease. L. pneumophila utilizes two main modes of iron assimilation, namely ferrous iron uptake via the FeoB system and ferric iron acquisition through the action of the siderophore legiobactin. This review highlights recent studies concerning the mechanism of legiobactin assimilation, the impact of c-type cytochromes on siderophore production, the importance of legiobactin in lung infection and a newfound role for a bacterial pyomelanin in iron acquisition. These data demonstrate that key aspects of L. pneumophila iron acquisition are significantly distinct from those of long-studied, 'model' organisms. Indeed, L. pneumophila may represent a new paradigm for a variety of other intracellular parasites, pathogens and under-studied bacteria.

Osteomyelitis of the patella caused by Legionella anisa.

A 51-year-old man with a history of stage IV angioimmunoblastic T-cell lymphoma was diagnosed with osteomyelitis of the patella. Legionella anisa was identified by 16S rRNA gene sequencing and culture. The patient had pneumonia 2 months prior to this osteomyelitis episode. L. anisa was retrospectively detected in his lung tissue by 16S rRNA gene sequencing and was considered the source of the L. anisa that caused his patella osteomyelitis.

VipD of Legionella pneumophila targets activated Rab5 and Rab22 to interfere with endosomal trafficking in macrophages.

Upon phagocytosis, Legionella pneumophila translocates numerous effector proteins into host cells to perturb cellular metabolism and immunity, ultimately establishing intracellular survival and growth. VipD of L. pneumophila belongs to a family of bacterial effectors that contain the N-terminal lipase domain and the C-terminal domain with an unknown function. We report the crystal structure of VipD and show that its C-terminal domain robustly interferes with endosomal trafficking through tight and selective interactions with Rab5 and Rab22. This domain, which is not significantly similar to any known protein structure, potently interacts with the GTP-bound active form of the two Rabs by recognizing a hydrophobic triad conserved in Rabs. These interactions prevent Rab5 and Rab22 from binding to downstream effectors Rabaptin-5, Rabenosyn-5 and EEA1, consequently blocking endosomal trafficking and subsequent lysosomal degradation of endocytic materials in macrophage cells. Together, this work reveals endosomal trafficking as a target of L. pneumophila and delineates the underlying molecular mechanism.

Legionella jordanis in hematopoietic SCT patients radiographically mimicking invasive mold infection.

Opportunistic pulmonary infections are a major cause of post-transplant morbidity and mortality. Among these infections, Aspergillus is a common cause of fatal pneumonia. Owing to the precarious clinical condition of many patients who acquire invasive mold infections, clinicians often treat them on the basis of radiographic findings, such as the halo sign. However, in patients who do not respond to treatment or who have uncommon presentations, bronchoscopy or lung biopsy looking for other pathogens should be considered. This study describes two cases in which the radiographic halo signs characteristic of Aspergillus were in fact due to Legionella jordanis, a pathogen that has been culture proven only in two patients previously (both of whom had underlying lung pathology) and diagnosed by serologic evidence in several other patients. In immunocompromised patients, Legionella can present as a cavitary lesion. Thus, presumptive treatment for this organism should be considered in post-transplant patients who do not have a classic presentation for invasive fungal infection and/or who fail to respond to conventional treatment. These cases illustrate the importance of obtaining tissue cultures to differentiate among the wide variety of pathogens present in this patient population.

Pneumonia due to Legionella feeleii: case report and review of the literature.

Legionella feeleii is a rare cause of community-acquired pneumonia that occurs in immunocompromised hosts who are often receiving corticosteroid therapy. We report a 69-year-old man who underwent bone marrow transplantation and developed pneumonia due to L. feeleii, and review the clinical characteristics of 7 cases of L. feeleii infection reported in the literature.

V gamma 9V delta 2 T cells in human legionellosis.

In humans, expansion of circulating Vgamma9Vdelta2 T cells seems to be a pathophysiological denominator shared by protozoan and intracellular bacterial diseases. The assumption was tested here on legionellosis, a condition conforming to the category but not yet described with respect to gammadelta T cells. Levels of Vgamma9Vdelta2 T cells in peripheral blood were measured at various intervals in 14 subjects undergoing a Pontiac fever-like disease, shown by serological investigation to be caused by Legionella micdadei. In samples obtained 4 to 6 days after the onset of the disease, the mean percentage (+/- the standard deviation) of Vgamma9Vdelta2+ T cells among CD3+ cells was 1.0% +/- 0.5%, compared to 5.0% +/- 3.9% in healthy control subjects (P < 0.001). Thereafter, a pronounced increase occurred and at 2 to 7 weeks after onset, mean peak levels were as high as approximately equal to 15%. During the next 6 months, values slowly declined, although without reaching the normal range. Percentages of gammadelta+ T cells expressing tumor necrosis factor alpha or gamma interferon in response to phorbol myristate acetate were assayed in vitro. At 14 to 16 days after the onset of disease, the expression of both cytokines was increased (P < 0.01), whereas at 5 to 7 weeks, the expression of tumor necrosis factor alpha was decreased (P < 0.05), possibly reflecting modulation of an inflammatory response. In conclusion, Pontiac fever was found to be associated with a pronounced and long-lasting expansion of Vgamma9Vdelta2 T cells, implying that the subset may also be pathophysiologically important in a mild and transient form of intracellular bacterial diseases. Surprisingly, the expansion was preceded by a depletion of circulatory Vgamma9Vdelta2 T cells. Possibly, Vgamma9Vdelta2 T cells are initially recruited to a site of infection before they expand in response to antigen and occur in high numbers in blood.

Comparison of virulence of Legionella longbeachae strains in guinea pigs and U937 macrophage-like cells.

A guinea pig model of experimental legionellosis was established for assessment of virulence of isolates of Legionella longbeachae. The results showed that there were distinct virulence groupings of L. longbeachae serogroup 1 strains based on the severity of disease produced in this model. Statistical analysis of the animal model data suggests that Australian isolates of L. longbeachae may be inherently more virulent than non-Australian strains. Infection studies performed with U937 cells were consistent with the animal model studies and showed that isolates of this species were capable of multiplying within these phagocytic cells. Electron microscopy studies of infected lung tissue were also undertaken to determine the intracellular nature of L. longbeachae serogroup 1 infection. The data showed that phagosomes containing virulent L. longbeachae serogroup 1 appeared bloated, contained cellular debris and had an apparent rim of ribosomes while those containing avirulent L. longbeachae serogroup 1 were compact, clear and smooth.

Entry and intracellular growth of Legionella dumoffii in alveolar epithelial cells.

We have found that Legionella dumoffii strain Tex-KL (ATCC 33343) invades into and proliferates in the human lung alveolar epithelial-cell line A549 in vitro. The organism associated with the A549 cells at a 10-fold greater magnitude than L. pneumophila Philadelphia-1 during in vitro coculture for 1 h. Thereafter, L. dumoffii Tex-KL invaded the cells at a significantly higher rate (100- to 1,000-fold) than did L. pneumophila Philadelphia-1. After internalization, however, both bacteria proliferated at the same rate. This in vitro finding led us to examine the bacterial localization in lungs in a fatal case of L. dumoffii pneumonia. Double immunostaining revealed the bacteria in surfactant apoprotein A-positive cells (i.e., type II alveolar epithelial cells). Next, we infected guinea pigs intratracheally with L. dumoffii Tex-KL. The animals became sick with a fever from 24 h to 48 h after infection with 10(4) to 10(9) cfu of L. dumoffii Tex-KL. The lung tissues were examined through electron microscopy at definite intervals. Many bacteria were found not only inside phagocytic cells in the alveolar space, but also in type I and type II alveolar epithelial cells. These findings strongly suggest that L. dumoffii has an ability to invade into and proliferate in human alveolar epithelial cells, which may explain the rapid and fulminant progress of pneumonia caused by L. dumoffii.

Legionella pericarditis diagnosed by direct fluorescent antibody staining.

Legionella pericarditis is a rare and serious manifestation of Legionnaire's disease. A case is presented in which the diagnosis was established by direct fluorescent antibody staining on a pericardial tissue specimen. Video-assisted thoracoscopy was used safely and effectively in diagnosis and management in this case.