A murine model for infection with Burkholderia cepacia with sustained persistence in the spleen

Unique Presentations of Burkholderia gladioli Infections in Several Strains of Immunocompromised Mice

Four strains of experimentally naïve mice (NOD. Cg-Prkdc scid Il2rg tm1Wjl /SzJ [NSG], NOD. Cg- Rag1 tm1Mom Il2rg tm1Wjl /SzJ [NRG], B6.129S(Cg)-Stat1 tm1Dlv/J [STAT1 -/-], and B6.129S7- Ifngr1 tm1Agt/J[IFNγR -/-] housed in a barrier facility developed unusual and seemingly unrelated clinical signs. Young NSG/NRG mice (n = 49, mean age = 4 ± 0.4 mo) exhibited nonspecific clinical signs of moderate-to-severe lethargy, hunched posture, decreased body condition, and pallor. In contrast to the NSG/NRG mice, the STAT1-/- and IFNγ R-/- mice (n = 5) developed large subcutaneous abscesses on the head and neck. These mice were euthanized, and samples were collected for culture. NSG/NRG mice had moderate-markedly enlarged livers (20 of 49, 40%) and spleens (17 of 49, 35%). The livers contained multiple, variably-sized, tan regions throughout all lobes. Histology revealed necrotizing hepatitis (13 of 17, 77%), splenic and hepatic extramedullary hematopoiesis (17 of 17, 100%), glomerular histiocytosis (6 of 17, 35%), and metritis (6 of 11, 55%) with perivascular inflammation, suggesting hematogenous spread Differentials for these lesions included mouse hepatitis virus, ectromelia virus, Pseudomonas aeruginosa, Salmonella spp., and Clostridium piliforme. Burkholderia gladioli was cultured from liver lesions and subcutaneous abscesses and confirmed with 16S ribosomal RNA sequencing. After completing systematic testing of the environment, failure of the water autoclave cycle was suspected as the cause of the outbreak. To address the situation, individually ventilated racks were sanitized and new breeders were purchased; these actions dramatically reduced B. gladioli infections. The current literature contains few reports of B. gladioli infections in immunocompromised mice, and its typical presentation is torticollis and rolling. B. gladioli infection is a potential differential for subcutaneous abscesses, hepatitis, and splenomegaly in immunocompromised mice. Careful monitoring of sterilization techniques is essential to prevent such infections in a barrier facility.

Characterization of the Burkholderia cenocepacia TonB Mutant as a Potential Live Attenuated Vaccine

Burkholderia cenocepacia is an opportunistic pathogen prevalent in cystic fibrosis patients, which is particularly difficult to treat, causing chronic and eventually fatal infections. The lack of effective treatment options makes evident the need to develop alternative therapeutic or prophylactic approaches. Vaccines, and live attenuated vaccines, are an unexplored avenue to treat B. cenocepacia infections. Here we constructed and characterized a B. cenocepacia tonB mutant strain, which was unable to actively transport iron, to test whether this single gene deletion mutant (strain renamed GAP001) protected against an acute respiratory B. cenocepacia lethal infection. Here we show that the mutant strain GAP001 is attenuated, and effective at protecting against B. cenocepacia challenge. Intranasal administration of GAP001 to BALB/c mice resulted in almost complete survival with high degree of bacterial clearance.

The art of persistence-the secrets to Burkholderia chronic infections

The Gram-negative proteobacteria genus Burkholderia encompasses multiple bacterial species that are pathogenic to humans and other vertebrates. Two pathogenic species of interest within this genus are Burkholderia pseudomallei (Bpm) and the B. cepacia complex (Bcc); the former is the causative agent of melioidosis in humans and other mammals, and the latter is associated with pneumonia in immunocompromised patients. One understudied and shared characteristic of these two pathogenic groups is their ability to persist and establish chronic infection within the host. In this review, we will explore the depth of knowledge about chronic infections caused by persistent Bpm and Bcc. We examine the host risk factors and immune responses associated with more severe chronic infections. We also discuss host adaptation and phenotypes associated with persistent Burkholderia species. Lastly, we survey how other intracellular bacteria associated with chronic infections are combatted and explore possible future applications to target Burkholderia Our goal is to highlight understudied areas that should be addressed for a more thorough understanding of chronic Burkholderia infections and how to combat them.

Burkholderia cepacia Complex Vaccines: Where Do We Go from here?

Burkholderia comprises a wide variety of environmental Gram-negative bacteria. Burkholderia cepacia complex (Bcc) includes several Burkholderia species that pose a health hazard as they are able to cause respiratory infections in patients with chronic granulomatous disease and cystic fibrosis. Due to the intrinsic resistance to a wide array of antibiotics and naturally occurring immune evasion strategies, treatment of Bcc infections often proves to be unsuccessful. To date, limited work related to vaccine development has been performed for Bcc pathogens. In this review, we have gathered key aspects of Bcc research that have been reported in recent years related to vaccine efforts, virulence, immune responses, and animal models, and use this information to inform the research community of areas of opportunity toward development of a viable Bcc vaccine.

Burkholderia cenocepacia creates an intramacrophage replication niche in zebrafish embryos, followed by bacterial dissemination and establishment of systemic infection

Bacteria belonging to the "Burkholderia cepacia complex" (Bcc) often cause fatal pulmonary infections in cystic fibrosis patients, yet little is know about the underlying molecular mechanisms. These Gram-negative bacteria can adopt an intracellular lifestyle, although their ability to replicate intracellularly has been difficult to demonstrate. Here we show that Bcc bacteria survive and multiply in macrophages of zebrafish embryos. Local dissemination by nonlytic release from infected cells was followed by bacteremia and extracellular replication. Burkholderia cenocepacia isolates belonging to the epidemic electrophoretic type 12 (ET12) lineage were highly virulent for the embryos; intravenous injection of <10 bacteria of strain K56-2 killed embryos within 3 days. However, small but significant differences between the clonal ET12 isolates K56-2, J2315, and BC7 were evident. In addition, the innate immune response in young embryos was sufficiently developed to control infection with other less virulent Bcc strains, such as Burkholderia vietnamiensis FC441 and Burkholderia stabilis LMG14294. A K56-2 cepR quorum-sensing regulator mutant was highly attenuated, and its ability to replicate and spread to neighboring cells was greatly reduced. Our data indicate that the zebrafish embryo is an excellent vertebrate model to dissect the molecular basis of intracellular replication and the early innate immune responses in this intricate host-pathogen interaction.

Role of excessive inflammatory response to Stenotrophomonas maltophilia lung infection in DBA/2 mice and implications for cystic fibrosis

Stenotrophomonas maltophilia is a pathogen that causes infections mainly in immunocompromised patients. Despite increased S. maltophilia isolation from respiratory specimens of patients with cystic fibrosis (CF), the real contribution of the microorganism to CF pathogenesis still needs to be clarified. The aim of the present study was to evaluate the pathogenic role of S. maltophilia in CF patients by using a model of acute respiratory infection in DBA/2 mice following a single exposure to aerosolized bacteria. The pulmonary bacterial load was stable until day 3 and then decreased significantly from day 3 through day 14, when the bacterial load became undetectable in all infected mice. Infection disseminated in most mice, although at a very low level. Severe effects (swollen lungs, large atelectasis, pleural adhesion, and hemorrhages) of lung pathology were observed on days 3, 7, and 14. The clearance of S. maltophilia observed in DBA/2 mouse lungs was clearly associated with an early and intense bronchial and alveolar inflammatory response, which is mediated primarily by neutrophils. Significantly higher levels of interleukin-1beta (IL-1beta), IL-6, IL-12, gamma interferon (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), GROalpha/KC, MCP-1/JE, MCP-5, macrophage inflammatory protein 1alpha (MIP-1alpha), MIP-2, and TARC were observed in infected mice on day 1 with respect to controls. Excessive pulmonary infection and inflammation caused systemic effects, manifested by weight loss, and finally caused a high mortality rate. Taken together, our results show that S. maltophilia is not just a bystander in CF patients but has the potential to contribute to the inflammatory process that compromises respiratory function.

Differential modulation of Burkholderia cenocepacia virulence and energy metabolism by the quorum-sensing signal BDSF and its synthase

Burkholderia cenocepacia produces the molecule cis-2-dodecenoic acid (BDSF), which was previously shown to play a role in antagonism against the fungal pathogen Candida albicans by interfering with its morphological transition. In this study, we show that production of BDSF is under stringent transcriptional control and the molecule accumulates in a cell density-dependent manner, typically found with quorum-sensing (QS) signals. B. cenocepacia mutant strain J2315 with a deleted Bcam0581 gene, which encodes an enzyme essential for BDSF production, exhibited a growth defect in minimal medium but not in rich medium, decreased virulence gene expression, and attenuated virulence in a zebrafish infection model. Exogenous addition of BDSF to the mutant rescues virulence gene expression but fails to restore its growth defect in minimal medium. We show that Bcam0581, but not BDSF, is associated with B. cenocepacia ATP biogenesis. We also provide evidence that some of the BDSF-regulated genes are also controlled by the acyl-homoserine-lactone-dependent QS system and are thus coregulated by two cell-to-cell signaling systems. These data demonstrate that in addition to the role in cross-kingdom signal interference, BDSF and its synthase are also important for the virulence and physiology of B. cenocepacia.

Identification of an RTX determinant of Burkholderia cenocepacia J2315 by subtractive hybridization

This study utilized suppressive subtractive hybridization between the clinical isolate Burkholderia cenocepacia J2315 and the closely related environmental isolate Burkholderia cepacia ATCC 25416T to isolate DNA fragments specific to B. cenocepacia J2315. Analysis of the resulting pools of B. cenocepacia-specific DNAs identified several fragments that may be part of putative virulence factors. Further in silico analysis of a single fragment indicated that it was internal to a gene of which the predicted product had characteristics of repeat in toxin (RTX)-like proteins and high similarity to proteins in other human or plant pathogens. In conjunction with this finding, phenotypic traits associated with known RTX proteins were assessed. A haemagglutinating activity of B. cenocepacia J2315 was identified that was absent in B. cepacia ATCC 25416T. The expression of this activity appeared to be growth phase-dependent. Analysis of the gene presence and haemagglutinating activity across the species of the B. cepacia complex showed that both were common to the ET12 lineage of B. cenocepacia, but were absent in the other species examined. Haemagglutinating activity was limited to isolates with the RTX-like gene. Expression studies utilizing quantitative PCR demonstrated an association between onset of haemagglutinating activity and increased expression of the gene, which suggests that the putative RTX determinant encodes a haemagglutinating activity.

Spontaneous septic arthritis caused by Burkholderia cepacia

We describe the first reported case of a spontaneous septic arthritis caused by Burkholderia cepacia, the organism responsible for onion skin rot. The source of infection was most likely from hematogenous spread, as the patient's blood cultures were positive for B. cepacia. Treatment involved arthroscopic irrigation and drainage of the affected shoulder. Despite post-operative resolution of this immunocompromised patient's shoulder symptoms, he was unable to survive the B. cepacia bacteremia. Our report not only describes the case but also reviews the difficulty in treating B. cepacia infections.

The multifarious, multireplicon Burkholderia cepacia complex

The Burkholderia cepacia complex (Bcc) is a collection of genetically distinct but phenotypically similar bacteria that are divided into at least nine species. Bcc bacteria are found throughout the environment, where they can have both beneficial and detrimental effects on plants and some members can also degrade natural and man-made pollutants. Bcc bacteria are now recognized as important opportunistic pathogens that can cause variable lung infections in cystic fibrosis patients, which result in asymptomatic carriage, chronic infection or 'cepacia syndrome', which is characterized by a rapid decline in lung function that can include invasive disease. Here we highlight the unique characteristics of the Bcc, focusing on the factors that determine virulence.

Colonial morphology of Burkholderia cepacia complex genomovar III: implications in exopolysaccharide production, pilus expression, and persistence in the mouse

The purpose of this study was to determine the role of colonial morphology of Burkholderia cepacia complex (BCC) organisms in pathogenicity in a mouse model of pulmonary infection. BCC strain C1394 was rapidly cleared by leukopenic mice after intranasal challenge, whereas a spontaneous variant (C1394mp2) that was indistinguishable from the parent strain by genetic typing persisted in the lungs and differed in colonial morphology. The parent strain had a matte colonial phenotype, made scant exopolysaccharide (EPS), and was lightly piliated. The variant had a shiny phenotype, produced abundant EPS, and was heavily piliated. Matte to shiny colonial transformation was induced by growth at 42 degrees C. Colonial morphology in the BCC strain variant was associated with persistence after pulmonary challenge and appeared to be correlated with the elaboration of putative virulence determinants.

Differential persistence among genomovars of the Burkholderia cepacia complex in a murine model of pulmonary infection

Cystic fibrosis patients infected with strains from different genomovars of the Burkholderia cepacia complex can experience diverse clinical outcomes. To identify genomovar-specific determinants that might be responsible for these differences, we developed a pulmonary model of infection in BALB/c mice. Mice were rendered leukopenic by administration of cyclophosphamide prior to intranasal challenge with 1.6 x 10(4) bacteria. Five of six genomovar II strains persisted at stable numbers in the lungs until day 16 with minimal toxicity, whereas zero of seven genomovar III strains persisted but resulted in variable toxicity. We have developed a chronic pulmonary model of B. cepacia infection which reveals differences among genomovars in terms of clinical infection outcome.

Correlation between an in vitro invasion assay and a murine model of Burkholderia cepacia lung infection

Our understanding of the virulence of Burkholderia cepacia complex lung infections in cystic fibrosis patients is incomplete. There is a great deal of variability in the clinical course, from simple colonization to severe and often fatal necrotizing pneumonia, termed cepacia syndrome. Multiple subspecies (called genomovars) have been identified, and these genomovars may hold the key to understanding the variable pathogenicity. Thirty-one B. cepacia complex isolates belonging to five of the seven genomovars were examined by using a gentamicin protection assay of invasion with A549 cells. The level of epithelial cell invasion by B. cepacia in the A549 model was relatively low compared with the data obtained for other pathogens and was often variable from assay to assay. Thus, a statistical approach was used to determine invasiveness. When this model was used, one of four genomovar I strains (25%), three of eight genomovar II strains (37.5%), seven of nine genomovar III strains (77.8%), one of four genomovar IV strains (25%), and none of the four genomovar V strains examined were defined as invasive. All other strains were categorized as either noninvasive or indeterminate. Invasive, noninvasive, and indeterminate isolates belonging to genomovars II and III were subsequently tested for splenic invasion with the mouse agar bead model. Correlation between the models for six strains was demonstrated. Our results indicate that a statistical model used to determine invasiveness in an in vitro invasion assay can be used to predict in vivo invasiveness.

Enhanced susceptibility to pulmonary infection with Burkholderia cepacia in Cftr(-/-) mice

Progressive pulmonary infection is the dominant clinical feature of cystic fibrosis (CF), but the molecular basis for this susceptibility remains incompletely understood. To study this problem, we developed a model of chronic pneumonia by repeated instillation of a clinical isolate of Burkholderia cepacia (genomovar III, ET12 strain), an opportunistic gram-negative bacterium, from a case of CF into the lungs of Cftr (m1unc-/-) (Cftr(-/-)) and congenic Cftr(+/+) controls. Nine days after the last instillation, the CF transmembrane regulator knockout mice showed persistence of viable bacteria with chronic severe bronchopneumonia while wild-type mice remained healthy. The histopathological changes in the lungs of the susceptible Cftr(-/-) mice were characterized by infiltration of a mixed inflammatory-cell population into the peribronchiolar and perivascular spaces, Clara cell hyperplasia, mucus hypersecretion in airways, and exudation into alveolar airspaces by a mixed population of macrophages and neutrophils. An increased proportion of neutrophils was observed in bronchoalveolar lavage fluid from the Cftr(-/-) mice, which, despite an increased bacterial load, demonstrated minimal evidence of activation. Alveolar macrophages from Cftr(-/-) mice also demonstrated suboptimal activation. These observations suggest that the pulmonary host defenses are compromised in lungs from animals with CF, as manifested by increased susceptibility to bacterial infection and lung injury. This murine model of chronic pneumonia thus reflects, in part, the situation in human patients and may help elucidate the mechanisms leading to defective host defense in CF.

Cellular aspects of Burkholderia cepacia infection

The Gram-negative bacterium Burkholderia cepacia has recently emerged as an important opportunistic pathogen in humans. This review focuses on the cellular aspects of B. cepacia infection and the dynamics of the B. cepacia-host cell interaction, including recent advances in our understanding of the ability of B. cepacia to adhere to, enter, and survive intracellularly within human cells.

Outbreak of subclinical mastitis in a flock of dairy sheep associated with Burkholderia cepacia complex infection

An outbreak of subclinical mastitis in a flock of 620 milking sheep was investigated. Microbiological and epidemiological analyses identified the causative agent as belonging to the Burkholderia cepacia complex (formerly Pseudomonas cepacia). Every ewe in the milking flock was individually tested for subclinical mastitis on two separate occasions, 6 weeks apart, by the California (rapid) mastitis test (CMT). The proportion of CMT-positive ewes was 69 of 393 (17.6%) on the first sampling and 27 of 490 (5.5%) on the second sampling. Pure B. cepacia cultures identified with the API 20 NE system were grown from 64 of 96 (66.7%) CMT-positive ewes and from 1 of 33 (3.0%) CMT-negative ewes. Statistical analysis confirmed the significant association between a positive CMT result and a positive culture result for B. cepacia complex. Additional polyphasic taxonomic analyses of eight isolates showed that seven belonged to B. cepacia genomovar III; the remaining isolate was identified as Burkholderia vietnamiensis (formerly B. cepacia genomovar V). Bacteriological investigation of samples from milking equipment and other environmental sites failed to identify "B. cepacia" in any of the samples taken. To our knowledge, this is the first report of an outbreak of natural infection in animals caused by B. cepacia complex and the first description of B. cepacia complex infection in sheep.