Update on the taxonomy and clinical aspects of the genus fusobacterium

Fusobacterium nucleatum and Tannerella forsythia induce synergistic alveolar bone loss in a mouse periodontitis model

Tannerella forsythia is strongly associated with chronic periodontitis, an inflammatory disease of the tooth-supporting tissues, leading to tooth loss. Fusobacterium nucleatum, an opportunistic pathogen, is thought to promote dental plaque formation by serving as a bridge bacterium between early- and late-colonizing species of the oral cavity. Previous studies have shown that F. nucleatum species synergize with T. forsythia during biofilm formation and pathogenesis. In the present study, we showed that coinfection of F. nucleatum and T. forsythia is more potent than infection with either species alone in inducing NF-κB activity and proinflammatory cytokine secretion in monocytic cells and primary murine macrophages. Moreover, in a murine model of periodontitis, mixed infection with the two species induces synergistic alveolar bone loss, characterized by bone loss which is greater than the additive alveolar bone losses induced by each species alone. Further, in comparison to the single-species infection, mixed infection caused significantly increased inflammatory cell infiltration in the gingivae and osteoclastic activity in the jaw bones. These data show that F. nucleatum subspecies and T. forsythia synergistically stimulate the host immune response and induce alveolar bone loss in a murine experimental periodontitis model.

Adherence to streptococci facilitates Fusobacterium nucleatum integration into an oral microbial community

The development of multispecies oral microbial communities involves complex intra- and interspecies interactions at various levels. The ability to adhere to the resident bacteria or the biofilm matrix and overcome community resistance are among the key factors that determine whether a bacterium can integrate into a community. Fusobacterium nucleatum is a prevalent Gram-negative oral bacterial species that is able to adhere to a variety of oral microbes and has been implicated in playing an important role in the establishment of multispecies oral microbial community. However, the majority of experiments thus far has focused on the physical adherence between two species as measured by in vitro co-aggregation assays, while the community-based effects on the integration of F. nucleatum into multispecies microbial community remains to be investigated. In this study, we focus on community integration of F. nucleatum. We demonstrated using an established in vitro mice oral microbiota (O-mix) that the viability of F. nucleatum was significantly reduced upon addition to the O-mix due to cell contact-dependent induction of hydrogen peroxide (H(2)O(2)) production by oral community. Interestingly, this inhibitory effect was significantly alleviated when F. nucleatum was allowed to adhere to its known interacting partner species (such as Streptococcus sanguinis) prior to addition. Furthermore, this aggregate formation-dependent protection was absent in the F. nucleatum mutant strain ΔFn1526 that is unable to bind to a number of Gram-positive species. More importantly, this protective effect was also observed during integration of F. nucleatum into a human salivary microbial community (S-mix). These results suggest that by adhering to other oral microbes, F. nucleatum is able to mask the surface components that are recognized by H(2)O(2) producing oral community members. This evasion strategy prevents detection by antagonistic oral bacteria and allows integration into the developing oral microbial community.

Investigation of the aetiology of udder-thigh dermatitis in French dairy cattle

Udder-thigh dermatitis (UTD) is a common disease in dairy cattle. The aim of this study was to define UTD incidence, its risk factors and the involved pathogens. Of 74 respondents, 72 (97%) reported having had the disease. On those farms the incidence was 5.3 cases per 100 cow years. The odds ratio (OR) of UTD in primiparous compared to multiparous cows was 23.4 (95% CI 17.3-33.8). Compared to tied stalls, the ORs of UTD were 0.65 (95% CI 0.45-0.92) and 0.43 (95% CI 0.24-0.71) for free stalls and straw yards, respectively. Udder oedema was reported in 98.3% of cows with UTD. The most common bacteria isolated from affected skin were Fusobacterium spp. (12/14 cases). This study suggests that UTD management should focus on local treatment, reducing udder oedema and increasing exercise.

Invasive potential of gut mucosa-derived Fusobacterium nucleatum positively correlates with IBD status of the host

BACKGROUND

Fusobacterium nucleatum is a heterogeneous oral pathogen that is also a common resident of the human gut mucosa. Given that some strains of F. nucleatum are known to be invasive and proinflammatory in the oral mucosa, we compared strains isolated from patients with inflammatory bowel disease (IBD) with strains isolated from healthy controls to determine 1) whether this species was more commonly associated with IBD patients; and 2) whether gut-derived F. nucleatum strains from IBD patients showed an increased capacity for invasion.

METHODS

Biopsy material was obtained from 56 adult patients undergoing colonoscopy for colon cancer screening purposes or assessment of irritable bowel syndrome status (34 patients), or to assess for presence of gastrointestinal disease (i.e., IBD or indeterminate colitis, 22 patients). We enumerated Fusobacterium spp. strains isolated from human gut biopsy material in a blinded fashion, and then compared the virulence potential of a subset of F. nucleatum strains using an invasion assay in a Caco-2 model system.

RESULTS

Fusobacterium spp. were isolated from 63.6% of patients with gastrointestinal disease compared to 26.5% of healthy controls (P = 0.01). In total, 69% of all Fusobacterium spp. recovered from patients were identified as F. nucleatum. F. nucleatum strains originating from inflamed biopsy tissue from IBD patients were significantly more invasive in a Caco-2 cell invasion assay than strains that were isolated from healthy tissue from either IBD patients or control patients (P < 0.05 to 0.001).

CONCLUSIONS

This study indicates that colonization of the intestinal mucosa by highly invasive strains of F. nucleatum may be a useful biomarker for gastrointestinal disease.

Fusobacterium nucleatum: an emerging gut pathogen?

The Gram-negative, non-sporulating, obligately anaerobic species, Fusobacterium nucleatum, is rapidly gaining notoriety as a pathogen with a surprising number of associated diseases. Recently, we have found that F. nucleatum is a more common resident of the GI tract than originally thought, and thus, through several studies, we have attempted to determine its gut-relevant potential for virulence. We have found that F. nucleatum possesses a number of pathogenic traits with relevance to gut diseases such as inflammatory bowel disease (IBD), however, we have also documented strain-associated differences in virulence. An intriguing picture emerges that paints F. nucleatum as both conferring beneficial as well as detrimental effects on host cells; and we suggest that the ultimate effects of F. nucleatum infection in the gut are a consequence of the microbes with which this species aggregates.

Fusobacterium nucleatum infection of colonic cells stimulates MUC2 mucin and tumor necrosis factor alpha

The etiology of inflammatory bowel disease is not completely known, but it is influenced by the presence of normal gut microflora as well as yet-unrecognized pathogens. The anaerobic, Gram-negative bacterial species Fusobacterium nucleatum is a common resident of the human mouth and gut and varies in its pathogenic potential. In this study, we demonstrate that highly invasive F. nucleatum isolates derived from the inflamed guts of Crohn's disease patients evoked significantly greater MUC2 and tumor necrosis factor alpha (TNF-α) gene expression than minimally invasive strains isolated from the noninflamed gut in human colonic epithelial cells and in a rat ligated colonic loop model of infection. Only live F. nucleatum induced mucin secretion and TNF-α expression in direct contact with and/or during invasion of colonic cells. In rat colons, mucin secretion was augmented in response to a highly invasive F. nucleatum isolate but was unaffected by treatment with a minimally invasive strain. Taken together, these studies reveal that F. nucleatum may represent a challenging pathogen in the etiology of gut inflammatory diseases and highlight the importance of different pathotypes of candidate bacterial species in disease pathogenesis.

Bloodstream infections due to Trichosporon spp.: species distribution, Trichosporon asahii genotypes determined on the basis of ribosomal DNA intergenic spacer 1 sequencing, and antifungal susceptibility testing

The reevaluation of the genus Trichosporon has led to the replacement of the old taxon Trichosporon beigelii by six new species. Sequencing of the ribosomal DNA (rDNA) intergenic spacer 1 (IGS1) is currently mandatory for accurate Trichosporon identification, but it is not usually performed in routine laboratories. Here we describe Trichosporon species distribution and prevalence of Trichosporon asahii genotypes based on rDNA IGS1 sequencing as well as antifungal susceptibility profiles of 22 isolates recovered from blood cultures. The clinical isolates were identified as follows: 15 T. asahii isolates, five Trichosporon asteroides isolates, one Trichosporon coremiiforme isolate, and one Trichosporon dermatis isolate. We found a great diversity of different species causing trichosporonemia, including a high frequency of isolation of T. asteroides from blood cultures that is lower than that of T. asahii only. Regarding T. asahii genotyping, we found that the majority of our isolates belonged to genotype 1 (86.7%). We report the first T. asahii isolate belonging to genotype 4 in South America. Almost 50% of all T. asahii isolates exhibited amphotericin B MICs of >or=2 microg/ml. Caspofungin MICs obtained for all the Trichosporon sp. isolates tested were consistently high (MICs >or= 2 microg/ml). Most isolates (87%) had high MICs for 5-flucytosine, but all of them were susceptible to triazoles, markedly to voriconazole (all MICs <or= 0.06 microg/ml).

Phenotypic and genotypic analyses of clinical Fusobacterium nucleatum and Fusobacterium periodonticum isolates from the human gut

Fusobacterium nucleatum is a Gram-negative anaerobic rod that is part of the normal human microflora, and has also been associated with various infections. Bacterial strains belonging to the species are typically heterogeneous in both phenotype and genotype, which can hinder their identification in a clinical setting. The majority of F. nucleatum isolates originate from oral sites, however the species is also a resident of the human gastrointestinal tract. The aim of this study was to compare F. nucleatum isolates from human intestinal biopsy samples to try and determine whether isolates from this site are divergent from oral isolates. We used a variety of phenotypic and genotypic markers to compare 21 F. nucleatum and Fusobacterium periodonticum isolates from the GI tract to oral isolates and recognized type strains in order to study heterogeneity within this set. 16S rDNA and rpoB gene sequence analysis allowed us to build phylogenetic trees that consistently placed isolates into distinct clusters. 16S rDNA copy number analyses using Denaturing Gradient Gel Electrophoresis (DGGE) demonstrated potential for use as a method to examine clonality amongst species. Phenotypic analyses gave variable results that were generally unhelpful in distinguishing between phylogenetic clusters. Our results suggest that a) F. periodonticum isolates are not restricted to the oral niche; b) phenotypic classification is not sufficient to subspeciate isolates; c) heterogeneity within the species is extensive but constrained; and d) F. nucleatum isolates from the gut tend to identify with the animalis subspecies.

Fusobacterial infections: clinical spectrum and incidence of invasive disease

OBJECTIVES

Clinically significant infections caused by members of the genus Fusobacterium are rare. We sought to describe the spectrum of clinical disease and epidemiology of these conditions presenting to an acute hospital over a five year period.

METHODS

Clinical records relating to consecutive laboratory isolates of Fusobacterium species were reviewed and cases classified according to pre-specified definitions of primary site and invasive infection.

RESULTS

78 Fusobacterium isolates were identified, 25 of which were associated with invasive disease, most commonly in men (76% of cases). Invasive Fusobacterium necrophorum infection of the head and neck was not observed in patients over 50. Invasive intra-abdominal disease was not observed amongst those under 60. 2 cases of Fusobacterium nucleatum bacteraemia were identified in neutropenic children. One retroperitoneal abscess may have represented secondary infection due to periodontitis. Obstetric infections were the most common clinical syndromes associated with isolates from the female genital tract. The incidence of invasive head and neck disease in the population aged 15-50 was 6.7 per million/year. There were no deaths.

CONCLUSIONS

Invasive fusobacterial infections are rare, affect distinct patient groups and are associated with good clinical outcomes in the majority of cases.

Fusobacterium equinum possesses a leukotoxin gene and exhibits leukotoxin activity

Fusobacterium equinum, a gram negative, rod-shaped and an obligate anaerobic bacterium is a newly described species. The organism is associated with necrotic infections of the respiratory tract in horses that include necrotizing pneumonia, pleuritis and paraoral infections. The species is closely related to F. necrophorum that causes liver abscesses in cattle and sheep, calf-diphtheria in cattle, and foot-rot in sheep and cattle. Leukotoxin, an exotoxin, is an important virulence factor in bovine strains of F. necrophorum. Our objective was to examine strains (n=10) of F. equinum for leukotoxin (lktA) gene and its toxic effects on equine leukocytes. Southern hybridization and partial DNA sequencing revealed that all the 10 strains had the lktA gene with greater similarities to F. necrophorum subsp. necrophorum. The secreted leukotoxin was detected in the culture supernatant and its biological activity was determined by viability assays with equine polymorphonuclear cells (PMNs) using flow cytometry. While culture supernatants of four strains (E1, E7, E9, and E10) were highly toxic to equine PMNs; strain E5 was moderately toxic and the remaining strains (E2, E3, E4, E6, and E8) were only mildly toxic. Our data indicated that F. equinum isolates had lktA gene and its product was toxic to equine leukocytes. Therefore, leukotoxin may be an important virulence factor in F. equinum infections.

Physiological alterations of a Fusobacterium nucleatum strain exposed to oxidative stress

AIM

The purpose of this study was to investigate the effect of oxidative stress on physiological and genetic characteristics of Fusobacterium nucleatum and its interference on this microbial identification methods.

METHODS AND RESULTS

Fus. nucleatum ssp. nucleatum ATCC 25586 (wt-strain) and an oxidative-stress-adapted strain derived from the wt-strain (aero-strain) were employed in the study. Cell-free crude protein extracts were obtained from both strains and differentially expressed proteins were identified by two-dimensional electrophoresis. Bacterium identification was performed by conventional biochemical tests, automated Rapid ID 32A system and specific PCR analysis. Genetic diversity between wt- and aero-strain was assessed by arbitrarily-primed (AP)-PCR. There were significant changes in the protein profile of aero-strain. The identification of the wt-strain was confirmed by all methods employed. Similar results were obtained for aero-strain when conventional biochemical tests and PCR were used. However, aero-strain was identified as Fusobacterium varium when submitted to Rapid ID 32A system. According to AP-PCR analysis, no significant genetic alteration was detected in aero-strain.

CONCLUSIONS

The adaptive response of Fus. nucleatum to oxidative stress is associated with changes on its biology, which may lead to misidentification of the organism, according to the conventional identification methods.

SIGNIFICANCE AND IMPACT OF THE STUDY

Oxidative stress may act as a cause of adaptive response in Fus. nucleatum with consequences to its biology, such as alterations on biochemical and physiological profile.

Human infection with Fusobacterium necrophorum (Necrobacillosis), with a focus on Lemierre's syndrome

Human infection with Fusobacterium necrophorum usually involves F. necrophorum subsp. funduliforme rather than F. necrophorum subsp. necrophorum, which is a common pathogen in animals. Lemierre's syndrome, or postanginal sepsis, is the most common life-threatening manifestation. Tonsillitis is followed by septic thrombophlebitis of the internal jugular vein and then a septicemia with septic emboli in lungs and other sites. Recent evidence suggests that F. necrophorum can be limited to the throat and cause persistent or recurrent tonsillitis. F. necrophorum is unique among non-spore-forming anaerobes, first for its virulence and association with Lemierre's syndrome as a monomicrobial infection and second because it seems probable that it is an exogenously acquired infection. The source of infection is unclear; suggestions include acquisition from animals or human-to-human transmission. Approximately 10% of published cases are associated with infectious mononucleosis, which may facilitate invasion. Recent work suggests that underlying thrombophilia may predispose to internal jugular vein thrombophlebitis. Lemierre's syndrome was relatively common in the preantibiotic era but seemed to virtually disappear with widespread use of antibiotics for upper respiratory tract infection. In the last 15 years there has been a rise in incidence, possibly related to restriction in antibiotic use for sore throat.

Proteomic investigation of glucose metabolism in the butyrate-producing gut anaerobeFusobacterium varium

A proteome survey and MS analysis were conducted to investigate glucose metabolism in Fusobacterium varium, a butyrate-producing constituent of the indigenous human gut microflora. The bacterium was capable of catabolizing glucose as the main energy source via the Embden-Meyerhof-Parnas pathway. 2-DE analyses revealed that the apparent concentrations of the six identified glycolytic enzymes (pyruvate kinase, enolase, glucose-6-phosphate isomerase, phosphoglycerate kinase, triosephosphate isomerase, and glyceraldehyde-3-phosphate dehydrogenase) were specifically increased in response to the presence of glucose in the chemically defined minimal growth medium, and did not diminish when the medium was additionally supplemented with L-glutamate, an amino acid readily fermented by members of the Fusobacterium genus. A substrate pool depletion study revealed that the sugar, and not the amino acid, is the more efficient growth substrate. Both proteomics and substrate pool depletion studies revealed that F. varium can simultaneously utilize both glucose and L-glutamate as energy sources. Enzymes involved in L-glutamate metabolism were also identified, including an NAD-dependent glutamate dehydrogenase and two enzymes of the methylaspartate pathway of L-glutamate catabolism (glutamate mutase and methylaspartate ammonia-lyase). Their apparent intracellular concentrations were elevated when the bacterium was cultured in media supplemented with excess L-glutamate. Our observation that the apparent concentrations of specific proteins were elevated in response to a particular growth substrate supplied as an energy source provides the first evidence for the presence of a nutrient-responsive mechanism governing intracellular protein concentration in F. varium.

Microarchitecture and Spatial Relationship Between Bacteria and Ileal, Cecal, and Colonic Epithelium in Chicks Fed a Direct-Fed Microbial, PrimaLac, and Salinomycin

Direct-fed microbials (DFM) could serve as a potential alternative to the feeding of antibiotics in poultry production. In this study, the effects of providing a DFM were compared with the feeding of salinomycin on intestinal histomorphometrics, and microarchitecture was examined. Broiler chicks (n=18 per treatment; trials 1 and 2) were fed a standard starter diet (control), control+PrimaLac (DFM; 0.3% wt/wt), and control+salinomycin (SAL; 50 ppm) from hatch to 21d. The birds were euthanized on d 21, and the ileal, jejunal, cecal, and colon tissues were dissected. Samples were examined by light microscopy (jejunum and ileum; trial 1) and scanning electron microscopy (ileum, cecum, and colon; trial 2). Feeding of the DFM increased intestinal muscle thickness (P<0.05) up to 33% compared with the control treatment. The DFM group also had increased villus height and perimeter (P=0.009 and 0.003, respectively) in jejunum. Segmented filamentous-like bacteria were less numerous in DFM-treated chicks than in the control chicks. Very few segmented filamentous-like bacteria were found near other microbes in the ileum. The DFM chicks had a larger number of bacteria positioned over or near goblet cells and in intervilli spaces. Bacteria in the colon were observed to be attached primarily around and within the crypts. Mucous thickness was less, and the density of bacteria embedded in the mucous blanket appeared to be lower in DFM-treated animals than in the control in all intestinal segments. The birds fed SAL had fewer bacteria and enterocytes in the ileum than in the control-and DFM-treated birds, and they had thicker and fewer microvilli. Because gastrointestinal track colonization by the DFM organisms can prevent the attachment of pathogens to the epithelium, spatial relationships, in this study, demonstrate the functionality of DFM and probiotics in preventing disease. It also supports previous observations that the feeding of salinomycin may alter intestinal function.

Rapid identification of Fusobacterium nucleatum and Fusobacterium necrophorum by fluorescence in situ hybridization

Identification of clinically relevant Fusobacterium spp. is hampered by their slow growth, their frequent occurrence in polymicrobial culture, and the low reliability of biochemical differentiation methods. A newly developed fluorescence in situ hybridization (FISH) assay allowed reliable and rapid identification of Fusobacterium necrophorum and Fusobacterium nucleatum from culture. Preliminary results show that the method offers the perspective for direct detection of these pathogens in blood cultures and abscess aspirates.

Lemierre's syndrome and genetic polymorphisms: a case report

Background

Lemierre's syndrome presents a classic clinical picture, the pathophysiology of which remains obscure. Attempts have been made to trace genetic predispositions that modify the host detection of pathogen or the resultant systemic reaction.

Case presentation

A 17-year old female, with no previous medical history, was admitted to the intensive care unit for septic shock, acute respiratory distress syndrome and Lemierre's syndrome. Her DNA was assayed for single nucleotide polymorphisms previously incriminated in the detection of the pathogen, the inflammatory response and the coagulation cascade. We observed functional variations in her Toll like 5 receptor (TLR 5) gene and two coagulation variations (Tissue Factor (TF) 603 and Plasminogen-Activator-Inhibitor-1 (PAI-1) 4G-4G homozygosity) associated with thrombotic events.

Conclusion

The innate immune response and the prothrombogenic mutations could explain, at least in part, the symptoms of Lemierre's syndrome. Genomic study of several patients with Lemierre's syndrome may reveal its pathophysiology.

The changing pattern of Fusobacterium infections in humans: recent experience with Fusobacterium bacteraemia

A retrospective study was conducted of 26 adult cases of fusobacterium bacteraemia that occurred between 1998 and 2003 at Center Hospitalier Universitaire de Grenoble, France. Most patients presented with pre-existing adverse medical conditions, including evolving malignant diseases (eight patients), recent surgery (four patients), and chronic organ failure (six patients). Only one patient presented with a classic Lemierre's syndrome. These results suggest an opportunistic pattern of modern fusobacterium infections.

Genotypic and phenotypic characterization of fusobacteria from Chinese and European patients with inflammatory periodontal diseases

Phylogenetic and antigenic studies were performed on 48 human oral Fusobacterium strains from Chinese patients with either necrotizing ulcerative gingivitis (NUG) or gingivitis and on 23 Fusobacterium nucleatum or Fusobacterium periodonticum strains from European periodontitis patients. Alignment of partial 16S rRNA gene sequences resulted in a phylogenetic tree that corresponded well with the current classification of oral fusobacteria into F. periodonticum and several subspecies of F. nucleatum, in spite of much minor genetic variability. F. periodonticum, F. nucleatum subsp. animalis and a previously undescribed phylogenetic cluster (C4), that may represent an additional F. nucleatum subspecies, constituted discrete clusters distinct from the remainder of F. nucleatum with high bootstrap values. Chinese and European strains differed markedly with regard to their respective classification patterns, suggesting a predominance of F. peridonticum and F. nucleatum susp. animalis over F. nucleatum subsp. nucleatum and F. nucleatum subsp. fusiforme/vincentii in samples from China. Antigenic typing enabled the association of many previously described serovars with distinct phylogenetic clusters and when applied directly to uncultured clinical samples confirmed the differential distribution of oral Fusobacterium taxa in Chinese and European samples. Bacteria from cluster C4 and F. nucleatum subsp. animalis were significantly more prevalent and accounted for higher cell numbers in NUG than in gingivitis samples, suggesting a possible association of these rarely observed taxa with NUG in Chinese patients.

Thyroid abscess due to a mixed anaerobic infection with Fusobacterium mortiferum

A rare case of a thyroid abscess due to mixed anaerobic flora containing Fusobacterium mortiferum in an immunocompetent patient is described. The patient was successfully treated with immediate surgical intervention and appropriate antimicrobial agents.

Enhanced pathogenicity of Fusobacterium nucleatum adapted to oxidative stress

Fusobacterium nucleatum is an obligate anaerobic bacterium found in the indigenous human microbiota but also recovered from several anaerobic infections. Considering the biological and medical relevance of F. nucleatum, the characterization of its response to oxidative stress is needed in order to understand how this anaerobic bacterium survives during an invasive process of oxygenated tissues. Influence of oxidative stress by atmospheric oxygen exposure on cellular morphology and pathogenicity of F. nucleatum were investigated. The wild-type F. nucleatum ATCC 25586 (wt-strain) was exposed to oxidative stress to select an adapted strain (aero-strain). Conventional NIH Swiss mice were split in two experimental groups which were challenged intraperitoneally with wt-strain and aero-strain, respectively, and a control group, unchallenged. Histopathological and hyperemia analysis were performed by day 30 after infection. Gram stain of aero-strain showed drastic changes in cellular morphology when compared to wt-strain. A significant increase of liver weight/body weight ratio (P < 0.05) as well as a tendency (P = 0.16) to higher spleen weight/body weight ratio were observed for the mice challenged with aero-strain when compared to the two other animal groups. Additionally, these animals also showed hyperemia in the spleen and liver as well as an increased number of inflammatory cells and steatosis in the liver. The results showed that, in addition to extensive changes in cell morphology, the adaptation to oxidative stress might also influence the pathogenicity of F. nucleatum. These findings have clinical implications since in the host tissues this indigenous putative pathogen is exposed to more or less oxygenated environments found on the different anatomic sites invaded by the bacterium.

Clindamycin-resistant Fusobacterium varium bacteremia and decubitus ulcer infection

Bacteremia due to Fusobacterium spp. is unusual (<10% of cases of anaerobic bacteremia), and the isolation of Fusobacterium varium is especially uncommon. The most probable sources of Fusobacterium bacteremia are the respiratory, the gastrointestinal, and the genitourinary tracts. A.-M. Bourgault et al. (Clin. Infect. Dis. 25[Suppl. 2]:181-183) described 40 patients with Fusobacterium bacteremia; only 3 had Fusobacterium varium, and no one had decubitus scars as the portal of entry. In another published series (S. Henry, A. De Maria, and W. R. McCabe, Am. J. Med. 75:225-231, 1983) of 26 cases, two patients had concomitant pulmonary lesions and decubitus ulcers but there was no identification to the species level mentioned. We report a case of Fusobacterium varium bacteremia and infected sacral decubitus ulcer in an elderly patient.

Fusobacterium necrophorum infections in animals: Pathogenesis and pathogenic mechanisms

Fusobacterium necrophorum, a Gram-negative, non-spore-forming anaerobe, is a normal inhabitant of the alimentary tract of animals and humans. Two subspecies of F. necrophorum, subsp. necrophorum (biotype A) and subsp. funduliforme (biotype B), have been recognized, that differ morphologically, biochemically, and biologically. The subsp. necrophorum is more virulent and is isolated more frequently from infections than the subsp. funduliforme. The organism is an opportunistic pathogen that causes numerous necrotic conditions (necrobacillosis), either specific or non-specific infections, in a variety of animals. Of these, bovine liver abscesses and foot rot are of significant concern to the cattle industry. Liver abscesses arise with the organisms that inhabit the rumen gaining entry into the portal circulation, and are often secondary to ruminal acidosis and rumenitis complex in grain-fed cattle. Foot rot is the major cause of lameness in dairy and beef cattle. The pathogenic mechanism of F. necrophorum is complex and not well defined. Several toxins or secreted products, such as leukotoxin, endotoxin, hemolysin, hemagglutinin, proteases, and adhesin, etc., have been implicated as virulence factors. The major virulence factor appears to be leukotoxin, a secreted protein of high molecular weight, active specifically against leukocytes from ruminants. The complete nucleotide sequence of the leukotoxin operon of F. necrophorum has been determined. The operon consists of three genes (lktBAC) of which the second gene (lktA) is the leukotoxin structural gene. The leukotoxin appears to be a novel protein and does not share sequence similarity with any other leukotoxin. F. necrophorum is also a human pathogen and the human strains appear to be different from the strains involved in animal infections.

Invasive infections caused by Trichosporon species and Geotrichum capitatum in patients with hematological malignancies: a retrospective multicenter study from Italy and review of the literature

Trichosporonosis is an uncommon but frequently fatal mycosis in immunocompromised patients. A multicenter retrospective study was conducted to characterize cases of proven or probable invasive trichosporonosis diagnosed over the past 20 years in Italian patients with hematological diseases. Of the 52 cases identified, 17 were classified as Trichosporon sp. infections and 35 were attributed to Geotrichum capitatum. Acute myeloid leukemia accounted for 65.4% of the cases. The incidence rates of Trichosporon sp. and G. capitatum infections in acute leukemia patients were 0.4 and 0.5%, respectively. Overall, 76.9% of cases had positive blood cultures. Pulmonary involvement was documented in 26.9% of cases. Death was reported for 57.1% of G. capitatum infections and for 64.7% of Trichosporon sp. infections. A literature review on trichosporonosis in patients with any underlying disease or condition reveals G. capitatum as a predominantly European pathogen, particularly in certain Mediterranean areas, while Trichosporon sp. infections are seen with similar frequencies on all continents. The majority of published Trichosporon sp. and G. capitatum infections occurred in patients with hematological diseases (62.8 and 91.7%, respectively). Well over half of these were suffering from acute leukemia (68 and 84% of patients with Trichosporon sp. and G. capitatum infections, respectively). Crude mortality rates were 77% for Trichosporon spp. and 55.7% for G. capitatum. The optimal therapy for trichosporonosis has yet to be identified; however, in vitro experiences are providing encouraging evidence of the potential role of the new triazoles, in particular, voriconazole.

Evolutionary relationships of Fusobacterium nucleatum based on phylogenetic analysis and comparative genomics

Background

The phylogenetic position and evolutionary relationships of Fusobacteria remain uncertain. Especially intriguing is their relatedness to low G+C Gram positive bacteria (Firmicutes) by ribosomal molecular phylogenies, but their possession of a typical gram negative outer membrane. Taking advantage of the recent completion of the Fusobacterium nucleatum genome sequence we have examined the evolutionary relationships of Fusobacterium genes by phylogenetic analysis and comparative genomics tools.

Results

The data indicate that Fusobacterium has a core genome of a very different nature to other bacterial lineages, and branches out at the base of Firmicutes. However, depending on the method used, 35–56% of Fusobacterium genes appear to have a xenologous origin from bacteroidetes, proteobacteria, spirochaetes and the Firmicutes themselves. A high number of hypothetical ORFs with unusual codon usage and short lengths were found and hypothesized to be remnants of transferred genes that were discarded. Some proteins and operons are also hypothesized to be of mixed ancestry. A large portion of the Gram-negative cell wall-related genes seems to have been transferred from proteobacteria.

Conclusions

Many instances of similarity to other inhabitants of the dental plaque that have been sequenced were found. This suggests that the close physical contact found in this environment might facilitate horizontal gene transfer, supporting the idea of niche-specific gene pools. We hypothesize that at a point in time, probably associated to the rise of mammals, a strong selective pressure might have existed for a cell with a Clostridia-like metabolic apparatus but with the adhesive and immune camouflage features of Proteobacteria.

Taxonomic changes of bacteria associated with endodontic infections

There have been major recent reorganizations among bacterial taxa as a result of phylogenetic taxonomic approaches. As a consequence, old species have been renamed and novel species have been proposed. The introduction of molecular technology for microbial identification has also allowed the detection of microbial taxa never previously found in endodontic infections. Therefore, the list of putative endodontic pathogens is frequently changing and expanding. The purpose of this review is twofold: to cover the taxonomic changes that the major putative endodontic pathogens have undergone in the recent years and to compile data from studies regarding the detection of known or novel bacterial species that had been only recently reported to occur in endodontic infections.

Disseminated trichosporonosis caused by Trichosporon loubieri

Trichosporonosis is an emerging invasive fungal infection in immunosuppressed patients; a case of disseminated infection caused by Trichosporon loubieri presented confirms its role as a human pathogen.