Dietary Fiber Drives IL-1ß-Dependent Peritonitis Induced by Bacteroides fragilis via Activation of the NLRP3 Inflammasome.

Intestinal barrier is essential for dietary products and microbiota compartmentalization and therefore gut homeostasis. When this barrier is broken, cecal content overflows into the peritoneal cavity, leading to local and systemic robust inflammatory response, characterizing peritonitis and sepsis. It has been shown that IL-1ß contributes with inflammatory storm during peritonitis and sepsis and its inhibition has beneficial effects to the host. Therefore, we investigated the mechanisms underlying IL-1ß secretion using a widely adopted murine model of experimental peritonitis. The combined injection of sterile cecal content (SCC) and the gut commensal bacteria Bacteroides fragilis leads to IL-1ß-dependent peritonitis, which was mitigated in mice deficient in NLRP3 (nucleotide-binding domain, leucine-rich-containing family, pyrin domain-containing-3) inflammasome components. Typically acting as a damage signal, SCC, but not B. fragilis, activates canonical pathway of NLRP3 promoting IL-1ß secretion in vitro and in vivo. Strikingly, absence of fiber in the SCC drastically reduces IL-1ß production, whereas high-fiber SCC conversely increases this response in an NLRP3-dependent manner. In addition, NLRP3 was also required for IL-1ß production induced by purified dietary fiber in primed macrophages. Extending to the in vivo context, IL-1ß-dependent peritonitis was worsened in mice injected with B. fragilis and high-fiber SCC, whereas zero-fiber SCC ameliorates the pathology. Corroborating with the proinflammatory role of dietary fiber, IL-1R-deficient mice were protected from peritonitis induced by B. fragilis and particulate bran. Overall, our study highlights a function, previously unknown, for dietary fibers in fueling peritonitis through NLRP3 activation and IL-1ß secretion outside the gut.

Characterization of the oxidative stress response regulatory network in Bacteroides fragilis: An interaction between BmoR and OxyR regulons promotes abscess formation in a model of intra-abdominal infection.

OBJECTIVES: Bacteroides fragilis is an anaerobic bacterium that is commonly found in the human gut microbiota and an opportunistic pathogen in extra-intestinal infections. B. fragilis displays a robust response to oxidative stress which allows for survival in oxygenated tissues such as the peritoneal cavity and lead to the formation of abscesses. In this study, we investigated the synergy of the oxidative stress response regulators OxyR and BmoR in the ability of B. fragilis to resist oxidative damage and to survive in extra-intestinal infection. METHODS: A ΔbmoR ΔoxyR double mutant B. fragilis strain was constructed, and its oxidative stress response was compared to parental and single mutant strains in phenotypical assays and gene expression analysis. The pathogenic potential in an in vivo mouse model of abscess formation was also evaluated. RESULTS: Expression analysis showed a coordinated control of thioredoxin C (trxC) gene expression by BmoR and OxyR during oxygen exposure, with upregulation of trxC in the bmoR mutant strain (4.9-fold increase), downregulation in the oxyR mutant (2.5-fold decrease), and an intermediate level of deregulation (2-fold increase) in the double mutant strain compared to the parent strain. Expression analysis during oxidative stress conditions also showed that BmoR is a major repressor of the CoA-disulfide reductase gene (upregulated 47-fold in the bmoR mutant) while OxyR plays a minor repression role in this gene (upregulated 2.5-fold in the oxyR mutant). Exposure to atmospheric oxygen for up to 72 h revealed that the deletion of bmoR alone had no significant effect in in vitro survival phenotype assays, though it partially abolishes the OxyR sensitivity phenotype in the bmoR/oxyR double mutant strain compared to oxyR mutant. In vivo assays showed that bmoR and oxyR mutants were significantly impaired in the formation and development of abscesses compared to the parent strain in an experimental intra-abdominal infection mouse model. CONCLUSION: Although the full extent of genes whose expression are modulated by BmoR and OxyR is yet to be defined, we present evidence that these regulators have overlapping functions in B. fragilis response to oxidative stress and ability to form abscess in extra-intestinal tissues.

Lactoferrin and lactoferricin B reduce adhesion and biofilm formation in the intestinal symbionts Bacteroides fragilis and Bacteroides thetaiotaomicron.

Several factors affect the composition of species that inhabit our intestinal tract, including mode of delivery, genetics and nutrition. Antimicrobial peptides and proteins secreted in the gastrointestinal tract are powerful tools against bacteria. Lactoferrin (LF) inhibits the growth of several bacterial species, such as Enterobacteriaceae, but may stimulate probiotic bacteria. Activity of LF against gut symbiotic species of the Bacteroides genus could give us insights on how these species colonize the gut. We investigated the effects of the antimicrobial protein lactoferrin and its derived peptide, lactoferricin B on two species of strict anaerobes, opportunistic pathogens that cause diseases in both adults and children, commonly found in the microbiota of the human gastrointestinal tract, Bacteroides fragilis and B. thetaiotaomicron., In vitro biofilm formation and binding to laminin were strongly inhibited by a low concentration of lactoferrin (12.5 µg/ml). Conversely, the growth of the strains in a micro-dilution assay in minimal media with different iron sources was not affected by physiological concentrations (2 mg/ml) of apo-lactoferrin or holo-lactoferrin. The combination of lactoferrin with antibiotics in synergism assays was also negative. The lactoferricin B fragment was also unable to inhibit growth in a similar test with concentrations of up to 32 µg/ml. Resistance to lactoferrin could confer an advantage to these species, even when high amount of this protein is present in the gastrointestinal tract. However, colonization is hampered by the binding and biofilm inhibitiory effect of lactoferrin, which may explain the low prevalence of Bacteroides in healthy babies. Resistance to this antimicrobial protein may help understand the success of these opportunistic pathogens during infection in the peritoneum.

Repression of Salmonella Host Cell Invasion by Aromatic Small Molecules from the Human Fecal Metabolome.

The human microbiome is a collection of microorganisms that inhabit every surface of the body that is exposed to the environment, generally coexisting peacefully with their host. These microbes have important functions, such as producing vitamins, aiding in maturation of the immune system, and protecting against pathogens. We have previously shown that a small-molecule extract from the human fecal microbiome has a strong repressive effect on Salmonella enterica serovar Typhimurium host cell invasion by modulating the expression of genes involved in this process. Here, we describe the characterization of this biological activity. Using a series of purification methods, we obtained fractions with biological activity and characterized them by mass spectrometry. These experiments revealed an abundance of aromatic compounds in the bioactive fraction. Selected compounds were obtained from commercial sources and tested with respect to their ability to repress the expression of hilA, the gene encoding the master regulator of invasion genes in Salmonella We found that the aromatic compound 3,4-dimethylbenzoic acid acts as a strong inhibitor of hilA expression and of invasion of cultured host cells by Salmonella Future studies should reveal the molecular details of this phenomenon, such as the signaling cascades involved in sensing this bioactive molecule.IMPORTANCE Microbes constantly sense and adapt to their environment. Often, this is achieved through the production and sensing of small extracellular molecules. The human body is colonized by complex communities of microbes, and, given their biological and chemical diversity, these ecosystems represent a platform where the production and sensing of molecules occur. In previous work, we showed that small molecules produced by microbes from the human gut can significantly impair the virulence of the enteric pathogen Salmonella enterica Here, we describe a specific compound from the human gut that produces this same effect. The results from this work not only shed light on an important biological phenomenon occurring in our bodies but also may represent an opportunity to develop drugs that can target these small-molecule interactions to protect us from enteric infections and other diseases.

Differential proteomic analysis of outer membrane enriched extracts of Bacteroides fragilis grown under bile salts stress.

Bacteroides fragilis is the most commonly isolated anaerobic bacteria from infectious processes. Several virulence traits contribute to the pathogenic nature of this bacterium, including the ability to tolerate the high concentrations of bile found in the gastrointestinal tract (GIT). The activity of bile salts is similar to detergents and may lead to membrane permeabilization and cell death. Modulation of outer membrane proteins (OMPs) is considered a crucial event to bile salts resistance. The primary objective of the current work was to identify B. fragilis proteins associated with the stress induced by high concentration of bile salts. The outer membrane of B. fragilis strain 638R was isolated after growth either in the presence of 2% conjugated bile salts or without bile salts. The membrane fractions were separated on SDS-PAGE and analyzed by ESI-Q/TOF tandem mass spectrometry. A total of 37 proteins were identified; among them nine were found to be expressed exclusively in the absence of bile salts whereas eight proteins were expressed only in the presence of bile salts. These proteins are related to cellular functions such as transport through membrane, nutrient uptake, and protein-protein interactions. This study demonstrates the alteration of OMPs composition in B. fragilis during bile salts stress resistance and adaptation to environmental changes. Proteomics of OMPs was also shown to be a useful approach in the identification of new targets for functional analyses.

The Bfp60 surface adhesin is an extracellular matrix and plasminogen protein interacting in Bacteroides fragilis.

Plasminogen (Plg) is a highly abundant protein found in the plasma component of blood and is necessary for the degradation of fibrin, collagen, and other structural components of tissues. This fibrinolytic system is utilized by several pathogenic species of bacteria to manipulate the host plasminogen system and facilitate invasion of tissues during infection by modifying the activation of this process through the binding of Plg at their surface. Bacteroides fragilis is the most commonly isolated Gram-negative obligate anaerobe from human clinical infections, such as intra-abdominal abscesses and anaerobic bacteraemia. The ability of B. fragilis to convert plasminogen (Plg) into plasmin has been associated with an outer membrane protein named Bfp60. In this study, we characterized the function of Bfp60 protein in B. fragilis 638R by constructing the bfp60 defective strain and comparing its with that of the wild type regarding binding to laminin-1 (LMN-1) and activation of Plg into plasmin. Although the results showed in this study indicate that Bfp60 surface protein of B. fragilis is important for the recognition of LMN-1 and Plg activation, a significant slow activation of Plg into plasmin was observed in the mutant strain. For that reason, the possibility of another unidentified mechanism activating Plg is also present in B. fragilis cannot be discarded. The results demonstrate that Bfp60 protein is responsible for the recognition of laminin and Plg-plasmin activation. Although the importance of this protein is still unclear in the pathogenicity of the species, it is accepted that since other pathogenic bacteria use this mechanism to disseminate through the extracellular matrix during the infection, it should also contribute to the virulence of B. fragilis.

Microbial diversity and anaerobic hydrocarbon degradation potential in an oil-contaminated mangrove sediment.

BACKGROUND: Mangrove forests are coastal wetlands that provide vital ecosystem services and serve as barriers against natural disasters like tsunamis, hurricanes and tropical storms. Mangroves harbour a large diversity of organisms, including microorganisms with important roles in nutrient cycling and availability. Due to tidal influence, mangroves are sites where crude oil from spills farther away can accumulate. The relationship between mangrove bacterial diversity and oil degradation in mangrove sediments remains poorly understood. RESULTS: Mangrove sediment was sampled from 0-5, 15-20 and 35-40 cm depth intervals from the Suruí River mangrove (Rio de Janeiro, Brazil), which has a history of oil contamination. DGGE fingerprinting for bamA, dsr and 16S rRNA encoding fragment genes, and qPCR analysis using dsr and 16S rRNA gene fragment revealed differences with sediment depth. CONCLUSIONS: Analysis of bacterial 16S rRNA gene diversity revealed changes with depth. DGGE for bamA and dsr genes shows that the anaerobic hydrocarbon-degrading community profile also changed between 5 and 15 cm depth, and is similar in the two deeper sediments, indicating that below 15 cm the anaerobic hydrocarbon-degrading community appears to be well established and homogeneous in this mangrove sediment. qPCR analysis revealed differences with sediment depth, with general bacterial abundance in the top layer (0-5 cm) being greater than in both deeper sediment layers (15-20 and 35-40 cm), which were similar to each other.

Detection of cross-infection associated to a Brazilian PCR-ribotype of Clostridium difficile in a university hospital in Rio de Janeiro, Brazil.

Clostridium difficile is an important nosocomial enteric pathogen and is the etiological agent of pseudomembranous colites. Recently, the rates of C. difficile infection (CDI) have increased worldwide, but in Brazil few data about this situation and the incidence of clonal types of C. difficile exist. This study aimed to isolate and characterize C. difficile strains from samples obtained of a university hospital (HUCFF) in Rio de Janeiro city, Brazil. CDI was identified by ELISA in 27.1% of HUCFF-in-patients enrolled in the study, and the bacterium was recovered from eight of these fecal samples. All strains, except one, presented tcdA and tcdB genes and presented neither the cdtA and cdtB genes nor any significant deletions in the tcdC gene. All strains were sensitive to metronidazole, vancomycin and moxifloxacin, and resistant to clindamycin, ciprofloxacin and levofloxacin. PCR-ribotyping and PFGE revealed four different clonal types among the isolates. The Brazilian PCR-ribotype 133 accounted for 50% of strains isolated, and PCR-ribotype 233 strains were obtained from 25% of the in-patients. The prevalence and resurgence of the Brazilian PCR-ribotype 133 among the hospitalized patients of HUCFF was established, and cross-infection of different patients associated to the same PCR-ribotypes was detected. Our results emphasize the importance of the diagnosis and control of CDI in order to prevent the emergence of specific clones that can lead to C. difficile-associated outbreaks in Brazilian hospitals.

Bioactive small molecules produced by the human gut microbiome modulate Vibrio cholerae sessile and planktonic lifestyles.

Humans live in symbiosis with a diverse community of microorganisms, which has evolved to carry out many specific tasks that benefit the host, including protection against invading pathogens. Within the chemical diversity of the gastrointestinal tract, small molecules likely constitute chemical cues for the communication between the microbiota and pathogens. Therefore, we sought to investigate if molecules produced by the human gut microbiota show biological activity against the human pathogen Vibrio cholerae. To probe the effects of the gut metabolome on V. cholerae, we investigated its response to small-molecule extracts from human feces, from a complex bacterial community cultivated in vitro, and from culture supernatants of Enterocloster citroniae, Bacteroides thetaiotaomicron, and Bacteroides vulgatus. Using RNA sequencing, we determined the impact of the human gut metabolome on V. cholerae global gene expression. Among the genes downregulated in the presence of the fecal extract, the most overrepresented functional category was cell motility, which accounted for 39% of repressed genes. Repression of V. cholerae motility by the fecal extract was confirmed phenotypically, and E. citroniae extracts reproduced this phenotype. A complex in vitro microbial community led to increased motility, as did extracts from B. vulgatus, a species present in this community. Accordingly, mucin penetration was also repressed by fecal and E. citroniae extracts, suggesting that the phenotypes observed may have implications for host colonization. Together with previous studies, this work shows that small molecules from the gut metabolome may have a widespread, significant impact on microbe-microbe interactions established in the gut environment.

Detection of resistance genes and susceptibility patterns in Bacteroides and Parabacteroides strains.

Susceptibility to five antimicrobials was determined for Bacteroides spp. (n = 52) and Parabacteroides distasonis (n = 8). All isolates were susceptible to metronidazole. The resistance rates to ampicillin, cefoxitin, tetracycline and clindamycin were 98%, 9.6%, 65.3% and 19.2% of the Bacteroides strains, respectively. The genes cepA, cfiA, cfxA, tetQ, ermF and nim were found in 69.2%, 17.3% 9.6%, 50%, 7.7% and 3.8% for these strains respectively. All P. distasonis strains were resistant to ampicilin. Cefoxitin, tetracycline and clindamycin resistance rates were 75%, 87.5% and 50%, respectively. The ermF and nim genes were absent and 37.5%, 12.5%, 12.5% and 87.5% of this strains possessed cepA, cfiA, cfxA and tetQ genes, respectively. Ten cfiA gene positive strains of Bacteroides and Parabacteroides were submitted to E-test with imipenem and amoxicillin-clavulanate. The resistance rate to imipenem was 4.1% and 8.3% to amoxicillin-clavulanate. This feature is for the first time described in Brazil.

Adhesion of anaerobic periodontal pathogens to extracellular matrix proteins.

Extracellular matrix (ECM) proteins are highly abundant in the human body and can be found in various tissues, most prominently in connective tissue and basement membrane. For invasive bacterial pathogens, these structures function as physical barriers that block access to underlying tissues. The ability to bind and degrade these barriers is important for the establishment of infections and migration to other body sites. In the oral cavity, the ECM and the basement membrane (BM) are important components of the Junctional epithelium (JE) that closes the gap between the teeth surface and the mucosa. In periodontitis, the JE is breached by invading pathogenic bacteria, particularly strict anaerobic species. In periodontitis, invading microorganisms induce an unregulated and destructive host response through polymicrobial synergism and dysbiosis that attracts immune cells and contributes to the destruction of connective tissue and bone in the periodontal pocket. Colonization of the periodontal pocket is the first step to establish this infection, and binding to ECM is a major advantage in this site. Several species of strict anaerobic bacteria are implicated in acute and chronic periodontitis, and although binding to ECM proteins was studied in these species, few adhesins were identified so far, and the mechanisms involved in adhesion are largely unidentified. This review summarizes the data available on the interaction of strict anaerobic bacteria and components of the ECM.

Characterization of Clostridium difficile strains isolated from immunosuppressed inpatients in a hospital in Rio de Janeiro, Brazil.

The aim of this work was to identify and characterize Clostridium difficile strains from fecal and hospital environmental samples. C. difficile toxins were detected by ELISA in 28.5% of the analyzed samples. Four strains were isolated from immunosuppressed inpatients presenting antibiotic-associated diarrhea. All strains possessed tcdA and tcdB genes and did not present neither the cdtA and cdtB genes nor any significant deletions in the tcdC gene. PFGE and PCR-ribotyping analysis showed that two strains belonged to the same clonal type (ribotype 014) and the other two were grouped into ribotype 106, in spite of presenting a similar, but not identical genetic fingerprint. This report shows that for the first time ribotype 106 was found outside the United Kingdom. All isolates were equally sensitive to metronidazole. The ribotype 014 isolates were highly resistant to clindamycin, while the ribotype 106 isolates were resistant to all fluoroquinolones tested. This work reveals the spread of C. difficile in the hospital unit studied and the presence of three genetically related types, two of them presenting resistance to fluoroquinolones.

Enterotoxigenic and nontoxigenic Bacteroides fragilis strains isolated in Brazil.

The presence of enterotoxigenic Bacteroides fragilis and nontoxigenic B. fragilis (NTBF) among 109 strains isolated from 1980-2008 in Brazil were investigated by PCR. One strain, representing 0.9% of the total analyzed strains, harbored the bft gene which was identified as bft-1 isoform based on PCR-RFLP and sequencing. Forty-nine strains (44.9%) exhibited the NTBF pattern III which possesses the flanking region required for pathogenicity island acquisition in which the bft gene is codified. These data reinforce the potential of B. fragilis as an emerging enteropathogen in our country.

Deletion of BmoR affects the expression of genes related to thiol/disulfide balance in Bacteroides fragilis.

Bacteroides fragilis, an opportunistic pathogen and commensal bacterium in the gut, is one the most aerotolerant species among strict anaerobes. However, the mechanisms that control gene regulation in response to oxidative stress are not completely understood. In this study, we show that the MarR type regulator, BmoR, regulates the expression of genes involved in the homeostasis of intracellular redox state. Transcriptome analysis showed that absence of BmoR leads to altered expression in total of 167 genes. Sixteen of these genes had a 2-fold or greater change in their expression. Most of these genes are related to LPS biosynthesis and carbohydrates metabolism, but there was a significant increase in the expression of genes related to the redox balance inside the cell. A pyridine nucleotide-disulfide oxidoreductase located directly upstream of bmoR was shown to be repressed by direct binding of BmoR to the promoter region. The expression of two other genes, coding for a thiosulphate:quinone-oxidoreductase and a thioredoxin, are indirectly affected by bmoR mutation during oxygen exposure. Phenotypic assays showed that BmoR is important to maintain the thiol/disulfide balance in the cell, confirming its relevance to B. fragilis response to oxidative stress.

Bacteremia after Endodontic Procedures in Patients with Heart Disease: Culture and Molecular Analyses.

INTRODUCTION: Infective endocarditis (IE) is still associated with high mortality, and antibiotic prophylaxis strategies are under intense debate. We evaluated the incidence of bacteremia after root canal preparation in teeth with necrotic pulps and apical periodontitis. METHODS: Blood samples were taken before and 5 and 30 minutes after endodontic treatment in teeth with apical periodontitis from individuals at high (n = 21) or no risk (n = 11) for IE. The former received prophylactic antibiotic therapy. Bacteriologic samples were taken from root canals before chemomechanical preparation to confirm pulp infection. Samples were subjected to aerobic and anaerobic culture and quantitative real-time polymerase chain reaction (qPCR), the latter to determine the total bacterial and streptococcal levels. RESULTS: Culture revealed no bacteremia in all individuals. Analysis by qPCR showed that bacterial DNA occurred in all root canal samples. qPCR showed a similar incidence of bacteremia between patients who received or did not receive prophylactic antibiotic therapy (P > .05). In blood samples taken 5 minutes after endodontic procedures, bacteria were detected in 2 of 11 (18%) individuals not taking antibiotics and in 4 of 21 (19%) patients under prophylaxis. After 30 minutes, the incidence of bacteremia decreased to 2 of 21 (10%) in patients taking antibiotics and was undetectable in patients at no risk of IE. The incidence of bacteremia by streptococci was identical as that for total bacteria. CONCLUSIONS: No detectable bacteremia was evident by culture after treatment of infected root canals. Molecular analysis revealed bacterial DNA and streptococci in blood from some patients without a significant difference between individuals receiving or not receiving antibiotic prophylaxis.

Non-toxigenic pattern II and III Bacteroides fragilis strains: coexistence in the same host.

Diarrhoeic stool samples from 334 0-5-year-old children were analysed with respect to the incidence of Bacteroides fragilis as well as other enteropathogens. B. fragilis was recovered in 9.3% (31/334) of the samples, and 79 strains were examined for the presence of the bft gene or the BfPAI flanking region using polymerase chain reaction assays. No enterotoxigenic B. fragilis strains were detected. In 29% (9/31) of the samples the coexistence of both II and III non-toxigenic B. fragilis (NTBF) patterns could be seen. In 51.6% (16/31) of the samples there existed a pattern II NTBF only, and in 19.4% (6/31) only pattern III could be detected. Strains from the same patient representing different patterns were submitted to pulsed-field gel electrophoresis assays. Fingerprints obtained by this technique showed that there was strong heterogeneity among strains from different individuals. However, different patterns from the same individual shared 100% similarity.

Incidence and importance of Clostridium difficile in paediatric diarrhoea in Brazil.

Clostridium difficile strains were detected in 14 of 210 (6.7 %) faecal samples from children in Rio de Janeiro, Brazil, by cultivating faeces on cycloserine/cefoxitin/fructose agar after alcohol-shock. Two main groups of children were studied: inpatients (n = 96) and outpatients (n = 114). The inpatient group consisted of children on antibiotics or immunosuppressors who presented with diarrhoea and other children who did not present with diarrhoea and were not under an antibiotic or chemotherapeutic regimen. Among the outpatients, two groups were examined: namely, a group that comprised children who presented with diarrhoea and were occasionally under an antibiotic regimen and another group that comprised patients who were not taking antibiotics. After cytotoxic assay, toxigenic C. difficile (Cd tox+) strains were detected in 4.2 % of inpatients and 3.5 % of outpatients. Exclusion of other infectious causes of diarrhoea indicated a typical case of C. difficile-associated paediatric diarrhoea in the community. Among Cd tox+ isolates, no variations were detected by PCR for toxin A that employed primers NK9 and NKVO11. No resistance was found to metronidazole or vancomycin among strains that were isolated from children who presented with diarrhoea, but the MIC(50) and MIC(90) values for clindamycin were 6-8 and 16 microg ml(-1), respectively. Resistance to clindamycin seems to be more disseminated in strains from outpatients than in those from inpatients (P < 0.05). In conclusion, these data suggest that investigation for C. difficile infection should be taken into account in paediatric diarrhoea in both inpatients and outpatients in developing countries.

The interaction of Bacteroides fragilis with components of the human fibrinolytic system.

Bacteroides fragilis is a minor component of the intestinal microbiota and the most frequently isolated from intra-abdominal infections and bacteremia. Previously, our group has shown that molecules involved in laminin-1 (LMN-1) recognition were present in outer membrane protein extracts of B. fragilis MC2 strain. One of these proteins was identified and showed 98% similarity to a putative B. fragilis plasminogen-binding protein precursor, deposited in the public database. Thus, the objective of this work was to overexpress and further characterize this novel adhesin. The ability of B. fragilis MC2 strain and purified protein to convert plasminogen into plasmin was tested. Our results showed that B. fragilis strain MC2 strain adhered to both LMN-1 and plasminogen and this adhesion was inhibited by either LMN-1 or plasminogen. Regarding the plasminogen activation activity, both the whole bacterial cell and the purified protein converted plasminogen into plasmin similar to streptokinase used as a positive control. Bacterial receptors that recognize plasminogen bind to it and enhance its activation, transforming a nonproteolytic bacterium into a proteolytic one. We present in vitro evidence for a pathogenic function of the plasminogen receptor in promoting adherence to laminin and also the formation of plasmin by B. fragilis.

Association between the cfxA gene and transposon Tn4555 in Bacteroides distasonis strains and other Bacteroides species.

The Bacteroides genus, the most prevalent anaerobic bacteria of the intestinal tract, carries a plethora of the mobile elements, such as plasmids and conjugative and mobilizable transposons, which are probably responsible for the spreading of resistance genes. Production of beta-lactamases is the most important resistance mechanism including cephalosporin resistance to beta-lactam agents in species of the Bacteroides fragilis group. In our previous study, the cfxA gene was detected in B. distasonis species, which encodes a clinically significant broad-spectrum beta-lactamase responsible for widespread resistance to cefoxitin and other beta-lactams. Such gene has been associated with the mobilizable transposon Tn4555. Therefore, the aim of this study was to detect the association between the cfxA gene and the presence of transposon Tn4555 in 53 Bacteroides strains isolated in Rio de Janeiro, Brazil, by PCR assay. The cfxA gene was detected in 11 strains and the Tn4555 in 15. The transposon sequence revealed similarities of approximately 96% with the B. vulgatus sequence which has been deposited in GenBank. Hybridization assay was performed in attempt to detect the cfxA gene in the transposon. It was possible to associate the cfxA gene in 11 of 15 strains that harbored Tn4555. Among such strains, 9 presented the cfxA gene as well as Tn4555, but in 2 strains the cfxA gene was not detected by PCR assay. Our results confirm the involvement of Tn4555 in spreading the cfxA gene in Bacteroides species.