Enhanced pathogenicity of Fusobacterium nucleatum adapted to oxidative stress

Antimicrobial activity and inhibition of biofilm formation in vitro and on human dentine by silver nanoparticles/carboxymethyl-cellulose composites

OBJECTIVE

To evaluate the antimicrobial activity of a silver nanoparticles/carboxymethyl-cellulose (AgNPs/CMC) composite on in vitro and dentine disc heterogeneous biofilms.

DESIGN

AgNPs/CMC composite effect on normal human gingival fibroblast cells (HGF) viability was determined by the MTT reduction assay. In addition, we evaluated the antimicrobial effect of AgNPs/CMC composite on Candida albicans, Enterococcus faecalis, and Fusobacterium nucleatum growth in vitro and heterogeneous biofilms, as well as dentine disc biofilms.

RESULTS

Quasi-spherical AgNPs/CMC composites, with a mean 22.3 nm particle-size were synthesized. They were not toxic to HGF cells at concentrations tested that were antimicrobial, however they caused significant cytotoxicity (89 %, p <  0.05) at concentrations > 15 μg/mL. In vitro, they inhibited up to 67 %, 66 %, and 96 % C. albicans, E. faecalis, and F. nucleatum growth at concentrations ranging from 1.2 μg/mL to 9.6 μg/mL, as compared with untreated control. We also demonstrated significant (p <  0.05) 58 % biofilm reduction by 4.8 μg/mL AgNPs/CMC composite on human dentine discs.

CONCLUSION

AgNPs/CMC composite showed anti biofilm activity on monocultures, heterogenous cultures, and dentine discs, resulting a potentially effective alternative to prevent and eliminate infections after endodontic treatment.

Fusobacterium nucleatum in the Colorectum and Its Association with Cancer Risk and Survival: A Systematic Review and Meta-analysis

BACKGROUND

The gut microbiome, in particular Fusobacterium nucleatum, has been reported to play a role in colorectal cancer development and in patient prognosis. We aimed to perform a systematic review and meta-analysis of published studies to assess the prevalence of F. nucleatum in colorectal tumors and evaluate the association between F. nucleatum and colorectal cancer development and prognosis.

METHODS

MEDLINE, EMBASE, and Web of Science databases were systematically searched for studies published until January 2019. Random effects meta-analyses were used to assess the prevalence of F. nucleatum in patients with colorectal cancer or tissues relative to controls and survival in F. nucleatum-positive versus -negative patients.

RESULTS

Forty-five relevant articles were identified. Meta-analyses indicated higher odds of F. nucleatum being present in colorectal tissue samples from patients with colorectal cancer [n = 6 studies, pooled OR = 10.06; 95% confidence intervals (CI), 4.48-22.58] and individuals with colorectal polyps (n = 5 studies, pooled OR = 1.83; 95% CI, 1.07-3.16) compared with healthy controls. Similar results were apparent in fecal samples, and when comparing tumor with adjacent normal tissue. Meta-analyses indicated poorer survival in patients with colorectal cancer with high versus low F. nucleatum abundance (n = 5 studies, pooled HR = 1.87; 95% CI, 1.12-3.11).

CONCLUSIONS

A consistent increase in the prevalence and/or abundance of F. nucleatum in colorectal cancer tissue and fecal samples compared with controls was apparent. High abundance of F. nucleatum in colorectal tumors was also associated with poorer overall survival.

IMPACT

F. nucleatum could be useful as a diagnostic and prognostic marker for colorectal cancer or as a treatment target.

Fusobacterium nucleatum stimulates monocyte adhesion to and transmigration through endothelial cells

OBJECTIVE

Fusobacterium nucleatum (F. nucleatum) is an important pathogen in periodontitis. Previous studies have demonstrated its ability to spread via haematogenesis and modulate host immune responses. However, little is known regarding its effect on endothelial cells (ECs) and leukocytes. The aim of this study was to assess the effect of F. nucleatum on monocyte attachment and transmigration through ECs.

DESIGN

Human umbilical vein endothelial cells (HUVECs) and human leukemic monocyte (THP-1) cells were infected with F. nucleatum and assessed for monocyte adhesion, transendothelial migration, and HUVEC proliferation/apoptosis. Real-time PCR, western blotting and ELISA were performed to assess the expression of proinflammatory cytokines, adhesion molecules and chemokines in both cells.

RESULTS

F. nucleatum challenge significantly induced THP-1 cell adhesion and transmigration and markedly impaired cell proliferation and apoptosis in HUVECs. A parallel increase in vascular cell adhesion molecule-1, intercellular adhesion molecule-1 and E-selectin expression in HUVECs and an upregulation of tumour necrosis factor-α, interleukin (IL)-1β, IL-6, IL-8, and monocyte chemoattractant protein-1 in both HUVECs and THP-1 cells were observed. The expression of nuclear factor-kappa B was also enhanced in HUVECs and THP-1 cells upon F. nucleatum infection.

CONCLUSIONS

F. nucleatum triggers an inflammatory response against infection in cells and promotes the recruitment and transmigration of monocytes through ECs.

The bacterial aetiology of pleural empyema. A descriptive and comparative metagenomic study

OBJECTIVES

The view of pleural empyema as a complication of bacterial pneumonia is changing because many patients lack evidence of underlying pneumonia. To further our understanding of pathophysiological mechanisms, we conducted in-depth microbiological characterization of empyemas in clinically well-characterized patients and investigated observed microbial parallels between pleural empyemas and brain abscesses.

METHODS

Culture-positive and/or 16S rRNA gene PCR-positive pleural fluids were analysed using massive parallel sequencing of the 16S rRNA and rpoB genes. Clinical details were evaluated by medical record review. Comparative analysis with brain abscesses was performed using metagenomic data from a national Norwegian study.

RESULTS

Sixty-four individuals with empyema were included. Thirty-seven had a well-defined microbial aetiology, while 27, all of whom had community-acquired infections, did not. In the latter subset, Fusobacterium nucleatum and/or Streptococcus intermedius was detected in 26 patients, of which 18 had additional facultative and/or anaerobic species in various combinations. For this group, there was 65.5% species overlap with brain abscesses; predisposing factors included dental infection, minor chest trauma, chronic obstructive pulmonary disease, drug abuse, alcoholism and diabetes mellitus. Altogether, massive parallel sequencing yielded 385 bacterial detections, whereas culture detected 38 (10%) and 16S rRNA gene PCR/Sanger-based sequencing detected 87 (23%).

CONCLUSIONS

A subgroup of pleural empyema appears to be caused by a set of bacteria not normally considered to be involved in pneumonia. Such empyemas appear to have a similar microbial profile to oral/sinus-derived brain abscesses, supporting spread from the oral cavity, potentially haematogenously. We suggest reserving the term 'primary empyema' for these infections.

Indoleamine 2,3-dioxygenase expression regulates the survival and proliferation of Fusobacterium nucleatum in THP-1-derived macrophages

Fusobacterium nucleatum (Fn) is a tumor-associated obligate anaerobic bacterium, which has a role in the progression of colorectal cancer (CRC). Fn can invade and promote colon epithelial cells proliferation. However, how Fn survives and proliferates in its host cells remains largely unknown. In this study, we aimed to determine the molecular mechanisms underlying the morphology, survival, and proliferation of Fn in THP-1-derived macrophages (dTHP1). For the first time, we found that Fn is a facultative intracellular bacterium that can survive and limited proliferate in dTHP1 cells up to 72 h, and a live Fn infection can inhibit apoptosis of dTHP1 cells by activating the PI3K and ERK pathways. Both Fn bacteria and dTHP1 cells exhibit obvious morphological changes during infection. In addition, Infection of Fn-induced indoleamine 2,3-dioxygenase (IDO) expression by TNF-α-dependent and LPS-dependent pathway in a time-dependent and dose-dependent manner, and the IDO-induced low tryptophan and high kynurenine environment inhibited the intracellular multiplication of Fn in dTHP1 cells. IDO expression further impaired the function of peripheral blood lymphocytes, permitting the escape of Fn-infected macrophages from cell death. IDO inhibition abrogated this effect caused by Fn and relieved immune suppression. In conclusion, we identified IDO as an important player mediating intracellular Fn proliferation in macrophages, and inhibition of IDO may aggravate infection in Fn-associated tumor immunotherapy.

Bacterially-Associated Transcriptional Remodelling in a Distinct Genomic Subtype of Colorectal Cancer Provides a Plausible Molecular Basis for Disease Development

The relevance of specific microbial colonisation to colorectal cancer (CRC) disease pathogenesis is increasingly recognised, but our understanding of possible underlying molecular mechanisms that may link colonisation to disease in vivo remains limited. Here, we investigate the relationships between the most commonly studied CRC-associated bacteria (Enterotoxigenic Bacteroides fragilis, pks+ Escherichia coli, Fusobacterium spp., afaC+ E. coli, Enterococcus faecalis & Enteropathogenic E. coli) and altered transcriptomic and methylation profiles of CRC patients, in order to gain insight into the potential contribution of these bacteria in the aetiopathogenesis of CRC. We show that colonisation by E. faecalis and high levels of Fusobacterium is associated with a specific transcriptomic subtype of CRC that is characterised by CpG island methylation, microsatellite instability and a significant increase in inflammatory and DNA damage pathways. Analysis of the significant, bacterially-associated changes in host gene expression, both at the level of individual genes as well as pathways, revealed a transcriptional remodeling that provides a plausible mechanistic link between specific bacterial colonisation and colorectal cancer disease development and progression in this subtype; these included upregulation of REG3A, REG1A and REG1P in the case of high-level colonization by Fusobacterium, and CXCL10 and BMI1 in the case of colonisation by E. faecalis. The enrichment of both E. faecalis and Fusobacterium in this CRC subtype suggests that polymicrobial colonisation of the colonic epithelium may well be an important aspect of colonic tumourigenesis.

Massive parallel sequencing provides new perspectives on bacterial brain abscesses

Rapid development within the field of massive parallel sequencing (MPS) is about to bring this technology within reach for diagnostic microbiology laboratories. We wanted to explore its potential for improving diagnosis and understanding of polymicrobial infections, using bacterial brain abscesses as an example. We conducted a prospective nationwide study on bacterial brain abscesses. Fifty-two surgical samples were included over a 2-year period. The samples were categorized as either spontaneous intracerebral, spontaneous subdural, or postoperative. Bacterial 16S rRNA genes were amplified directly from the specimens and sequenced using Ion Torrent technology, with an average of 500,000 reads per sample. The results were compared to those from culture- and Sanger sequencing-based diagnostics. Compared to culture, MPS allowed for triple the number of bacterial identifications. Aggregatibacter aphrophilus, Fusobacterium nucleatum, and Streptococcus intermedius or combinations of them were found in all spontaneous polymicrobial abscesses. F. nucleatum was systematically detected in samples with anaerobic flora. The increased detection rate for Actinomyces spp. and facultative Gram-negative rods further revealed several species associations. We suggest that A. aphrophilus, F. nucleatum, and S. intermedius are key pathogens for the establishment of spontaneous polymicrobial brain abscesses. In addition, F. nucleatum seems to be important for the development of anaerobic flora. MPS can accurately describe polymicrobial specimens when a sufficient number of reads is used to compensate for unequal species concentrations and principles are defined to discard contaminant bacterial DNA in the subsequent data analysis. This will contribute to our understanding of how different types of polymicrobial infections develop.

Environmental stimuli shape biofilm formation and the virulence of periodontal pathogens

Periodontitis is a common inflammatory disease affecting the tooth-supporting structures. It is initiated by bacteria growing as a biofilm at the gingival margin, and communication of the biofilms differs in health and disease. The bacterial composition of periodontitis-associated biofilms has been well documented and is under continual investigation. However, the roles of several host response and inflammation driven environmental stimuli on biofilm formation is not well understood. This review article addresses the effects of environmental factors such as pH, temperature, cytokines, hormones, and oxidative stress on periodontal biofilm formation and bacterial virulence.

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.

Oxidative stress response in the opportunistic oral pathogen Fusobacterium nucleatum

The anaerobic, Gram-negative bacillus Fusobacterium nucleatum plays a vital role in oral biofilm formation and the development of periodontal disease. The organism plays a central bridging role between early and late colonizers within dental plaque and plays a protective role against reactive oxygen species. Using a two-dimensional gel electrophoresis and mass spectrometry approach, we have annotated 78 proteins within the proteome of F. nucleatum subsp. nucleatum and identified those proteins whose apparent intracellular concentrations change in response to either O(2)- or H(2)O(2)-induced oxidative stress. Three major protein systems were altered in response to oxidative stress: (i) proteins of the alkyl hydroperoxide reductase/thioredoxin reductase system were increased in intracellular concentration; (ii) glycolytic enzymes were modified by oxidation (i.e. D-glyceraldehyde 3-phosphate dehydrogenase, and fructose 6-phosphate aldolase) or increased in intracellular concentration, with an accompanying decrease in ATP production; and (iii) the intracellular concentrations of molecular chaperone proteins and related proteins (i.e. ClpB, DnaK, HtpG, and HrcA) were increased.

Biofilm formation enhances the oxygen tolerance and invasiveness of Fusobacterium nucleatum in an oral mucosa culture model

BACKGROUND

The present study evaluates the survival capability of Fusobacterium nucleatum strains in an aerobic environment and compares the invasive capability of F. nucleatum in biofilm and planktonic forms in an organotypic cell culture (OCC) model.

METHODS

Biofilms of F. nucleatum American Type Culture Collection (ATCC) 25586 or Anaerobe Helsinki Negative (AHN) 9508 were produced by culturing on semipermeable membranes on brucella agar plates. The oxygen tolerance of the F. nucleatum strains was examined by incubating 3-day-old anaerobically grown biofilms in an aerobic environment (CO(2) [5% in air] incubator) for an additional 48 hours. The OCC model was constructed by seeding keratinocytes on a fibroblast-containing collagen gel. In invasion assays, a 3-day-old anaerobically grown biofilm (and planktonic bacteria in solution as the control) was placed upside down on the top of OCC and incubated under 5% CO(2) for 24 hours. Invasion of the bacteria and morphologic changes in OCC were assessed using hematoxylin and eosin, Ki-67, and periodic acid-Schiff stainings.

RESULTS

In biofilms, both F. nucleatum strains continuously increased their cell numbers in an aerobic environment for 48 hours. After incubating the bacterial biofilm in contact with the OCC model, F. nucleatum AHN 9508 was able to pass through the epithelial/basement membrane barrier and invade the collagen matrix. The invasiveness of biofilm F. nucleatum ATCC 25586 was limited to the epithelium. Cytotoxic effects and invasiveness of F. nucleatum on the OCC were much stronger when the bacteria were in biofilms than in the planktonic form.

CONCLUSION

Biofilm formation regulates the survival and invasiveness of F. nucleatum in an aerobic environment.

Use of 2-D electrophoresis and ESI mass spectrometry techniques to characterize Fusobacterium nucleatum proteins up-regulated after oxidative stress

The genus Fusobacterium belongs to the Fusobacteriaceae family and is a Gram-negative obligate anaerobic bacterium found in the human oral microbiota. Even that Fusobacterium nucleatum cannot grow under aerobic conditions, they may exhibit aerotolerance as an adaptive response which could figure as an important virulence factor, during the stages of infection, when these anaerobes are shifted to aerobic conditions. In this regard, little is known about bacterial oxidative stress adaptive response and the influence of this adaptation on the host-bacteria relationship. We aimed to use both techniques 2-DE and Electrospray Ionization Mass Spectrometry (ESI-MS) to characterize proteins in F. nucleatum, after oxidative stress. We related three different proteins which were up-regulated by oxidative stress. As its genome is already sequenced, these proteins were found in data base search, by homology. Thus, by using techniques as ESI-Q/TOF-MS, in addition to 2-DE, the opportunity exists to gain a more holistic view of the bacterial proteome of human pathogens, to achieve a better understanding of species diversity and to elucidate the role of specific proteins in disease. This work represents one of the first studies using genetic and physiological approaches to understand the phenomenon of oxidative stress in F. nucleatum.

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.

The influence of molecular oxygen exposure on the biology ofPrevotella intermedia, with emphasis on its antibiotic susceptibility

AIM

This study focuses on investigating the molecular and physiological characteristics of Prevotella intermedia after molecular oxygen exposure (MOE) and the effect on drug susceptibility patterns.

METHODS AND RESULTS

Samples of P. intermedia were used as parent strains: ATCC25611 and four clinical isolates. Strains adapted to oxidative stress by MOS were obtained by the enrichment technique. Drug susceptibility was evaluated by minimal inhibitory concentrations (MIC) using agar dilution. Arbitrarily primed-polymerase chain reaction (AP-PCR) was used to evaluate the genetic diversity of all strains and physiological analyses were made by sodiumdodecylsulfate-polyacrylamide gel electrophoresis and two-dimensional electrophoresis of crude, cell-free extracts. The genetic profile showed that lineages with altered MIC values were selected after MOE. Overall, we found significant decrease in drug susceptibility for the aero-strains against all tested antimicrobials (amoxicillin, amoxicillin+clavulanic acid, clindamycin, chloramphenicol, ertapenen and metronidazole). We also observed markedly different protein expression patterns between the parent and selected aero-strains.

CONCLUSIONS

MOE induces changes in the genetic profile and protein expression patterns of P. intermedia that may also be linked to its drug resistance mechanisms.

SIGNIFICANCE AND IMPACT OF THE STUDY

The effects of MOE on anaerobic bacterial physiology and behaviour may influence antimicrobial susceptibility patterns with potential consequences to antimicrobial chemotherapy.

Effects of oxidative stress on the virulence profile of Prevotella intermedia during experimental infection in gnotobiotic mice

Prevotella intermedia is a component of the indigenous microbiota but is also responsible for anaerobic infections of the gastrointestinal tract and oral cavity. The aim of the present study was to investigate the influence of oxidative stress on the in vivo pathogenicity of P. intermedia. Germ-free mice were challenged intraperitoneally with parental (wt) or oxidative stress adapted (aero) strains. Bacterial virulence was evaluated by histopathology, hyperaemia and blood analysis [C-reactive protein (CRP), serum albumin and white blood cells (WBCs)], 3 and 10 days after challenge. CRP levels and WBC count were higher in animals challenged with the aero strain, and the albumin level was lower in this group, only 10 days after infection (P<0.05). Body weight gain was significantly reduced whereas hyperaemia and ratios of spleen/organ weight were increased in animals challenged with the aero strain (P<0.05). The liver of animals challenged with the aero strain showed hyperaemia, vasodilatation as well as an increase in the number of inflammatory cells and liver/organ weight ratio (P<0.05). Similar, but more discrete, alterations were observed in the small intestine of animals challenged with the aero strain. Studies on stress responses of this putative pathogen may help to better understand the aggressive potential and virulence markers of anaerobic bacteria.