Conditional adherence of Enterococcus faecalis to extracellular matrix proteins

A Novel PilR/PilS Two-Component System Regulates Necrotic Enteritis Pilus Production in Clostridium perfringens

Clostridium perfringens causes necrotic enteritis (NE) in poultry. A chromosomal locus (VR-10B) was previously identified in NE-causing C. perfringens strains that encodes an adhesive pilus (NE pilus), along with a two-component system (TCS) designated here as PilRS. While the NE pilus is important in pathogenesis, the role of PilRS remains to be determined. The current study investigated the function of PilRS, as well as the Agr-like quorum-sensing (QS) system and VirSR TCS in the regulation of pilin production. Isogenic pilR, agrB, and virR null mutants were generated from the parent strain CP1 by insertional inactivation using the ClosTron system, along with the respective complemented strains. Immunoblotting analyses showed no detectable pilus production in the CP1pilR mutant, while production in its complement (CP1pilR+) was greater than wild-type levels. In contrast, pilus production in the agrB and virR mutants was comparable or higher than the wild type but reduced in their respective complemented strains. When examined for collagen-binding activity, the pilR mutant showed significantly lower binding to most collagen types (types I to V) than parental CP1 (P ≤ 0.05), whereas this activity was restored in the complemented strain (P > 0.05). In contrast, binding of agrB and virR mutants to collagen showed no significant differences in collagen-binding activity compared to CP1 (P > 0.05), whereas the complemented strains exhibited significantly reduced binding (P ≤ 0.05). These data suggest the PilRS TCS positively regulates pilus production in C. perfringens, while the Agr-like QS system may serve as a negative regulator of this operon. IMPORTANCE Clostridium perfringens type G isolates cause necrotic enteritis (NE) in poultry, presenting a major challenge for poultry production in the postantibiotic era. Multiple factors in C. perfringens, including both virulent and nonvirulent, are involved in the development of the disease. We previously discovered a cluster of C. perfringens genes that encode a pilus involved in adherence and NE development, along with a predicted two-component regulatory system (TCS), designated PilRS. In the present study, we have demonstrated the role of PilRS in regulating pilus production and collagen binding of C. perfringens. In addition, the Agr-like quorum sensing signaling pathway was found to be involved in the regulation. These findings have identified additional targets for developing nonantibiotic strategies to control NE disease.

Genome sequence analysis reveals potential for virulence genes and multi-drug resistance in an Enterococcus faecalis 2A (XJ05) strain that causes lamb encephalitis

Background

Enterococcus is an important component of normal flora in human and animals, but in recent years, the pathogenicity of Enterococcus has been confirmed in clinical medicine. More and more animal infections have been reported in veterinary clinics. For the last decades, outbreaks of encephalitis in lambs have become much more common in Northern Xinjiang, China. Consequent studies have confirmed that these affected lambs had been commonly infected with E. faecalis. More than 60 E. faecalis were isolated from the brain of infected lambs, A highly virulent strain entitled E. faecalis 2A (XJ05) were selected, sequenced and analyzed.

Result

Using whole genome sequence and de novo assembly, 18 contigs with NGS and annotation were obtained. It is confirmed that the genome has a size of 2.9 Mb containing 2783 protein-coding genes, as well as 54 tRNA genes and 4 rRNA genes. Some key features of this strain were identified, which included 7 predicted antibiotic resistance genes and 18 candidate virulence factor genes.

Conclusion

The E. faecalis 2A (XJ05) genome is conspicuous smaller than E.faecalis V583, but not significantly different from other non-pathogenic E. faecalis. It carried 7 resistance genes including 4 kind of antibiotics which were consistent with the results of extensive drug resistance phenotypic, including aminoglycoside, macrolide, phenicol, and tetracycline. 2A (XJ05) also carried 18 new virulence factor genes related to virulence, hemolysin genes (cylA, cylB, cylM, cylL) may play an important role in lamb encephalitis by E. faecalis 2A (XJ05).

Identification of novel adhesins of M. tuberculosis H37Rv using integrated approach of multiple computational algorithms and experimental analysis

Pathogenic bacteria interacting with eukaryotic host express adhesins on their surface. These adhesins aid in bacterial attachment to the host cell receptors during colonization. A few adhesins such as Heparin binding hemagglutinin adhesin (HBHA), Apa, Malate Synthase of M. tuberculosis have been identified using specific experimental interaction models based on the biological knowledge of the pathogen. In the present work, we carried out computational screening for adhesins of M. tuberculosis. We used an integrated computational approach using SPAAN for predicting adhesins, PSORTb, SubLoc and LocTree for extracellular localization, and BLAST for verifying non-similarity to human proteins. These steps are among the first of reverse vaccinology. Multiple claims and attacks from different algorithms were processed through argumentative approach. Additional filtration criteria included selection for proteins with low molecular weights and absence of literature reports. We examined binding potential of the selected proteins using an image based ELISA. The protein Rv2599 (membrane protein) binds to human fibronectin, laminin and collagen. Rv3717 (N-acetylmuramoyl-L-alanine amidase) and Rv0309 (L,D-transpeptidase) bind to fibronectin and laminin. We report Rv2599 (membrane protein), Rv0309 and Rv3717 as novel adhesins of M. tuberculosis H37Rv. Our results expand the number of known adhesins of M. tuberculosis and suggest their regulated expression in different stages.

The PavA-like fibronectin-binding protein of Enterococcus faecalis, EfbA, is important for virulence in a mouse model of ascending urinary tract infection

Enterococcus faecalis is an established nosocomial pathogen, yet the pathogenesis of enterococcal infections, particularly of urinary tract infections (UTIs), remains to be fully elucidated. Fibronectin-binding proteins have been identified as potent adhesins in pathogenic Gram-positive cocci. Here, we characterized EfbA, which is encoded by the enterococcal orthologue of Streptococcus pneumoniae pavA. Similar to PavA, the anchorless EfbA protein was localized to the enterococcal cell outer surface and bound to immobilized human fibronectin. In addition to abrogated EfbA expression, deletion of the efbA gene eliminated EfbA from the cell surface and drastically reduced the enterococcal cell binding to immobilized fibronectin. The ΔefbA deletion mutant was highly attenuated vs wild-type in a murine ascending UTI model, consistent with an increased tropism for the kidney relative to the bladder. These results provide the first evidence that EfbA of E. faecalis plays a role in UTIs, probably contributing to the pathogenesis in this site.

Human pathogens utilize host extracellular matrix proteins laminin and collagen for adhesion and invasion of the host

Laminin (Ln) and collagen are multifunctional glycoproteins that play an important role in cellular morphogenesis, cell signalling, tissue repair and cell migration. These proteins are ubiquitously present in tissues as a part of the basement membrane (BM), constitute a protective layer around blood capillaries and are included in the extracellular matrix (ECM). As a component of BMs, both Lns and collagen(s), thus function as major mechanical containment molecules that protect tissues from pathogens. Invasive pathogens breach the basal lamina and degrade ECM proteins of interstitial spaces and connective tissues using various ECM-degrading proteases or surface-bound plasminogen and matrix metalloproteinases recruited from the host. Most pathogens associated with the respiratory, gastrointestinal, or urogenital tracts, as well as with the central nervous system or the skin, have the capacity to bind and degrade Lns and collagen(s) in order to adhere to and invade host tissues. In this review, we focus on the adaptability of various pathogens to utilize these ECM proteins as enhancers for adhesion to host tissues or as a targets for degradation in order to breach the cellular barriers. The major pathogens discussed are Streptococcus, Staphylococcus, Pseudomonas, Salmonella, Yersinia, Treponema, Mycobacterium, Clostridium, Listeria, Porphyromonas and Haemophilus; Candida, Aspergillus, Pneumocystis, Cryptococcus and Coccidioides; Acanthamoeba, Trypanosoma and Trichomonas; retrovirus and papilloma virus.

The Fsr quorum-sensing system of Enterococcus faecalis modulates surface display of the collagen-binding MSCRAMM Ace through regulation of gelE

Ace, a known virulence factor and the first identified microbial surface component recognizing adhesive matrix molecule (MSCRAMM) of Enterococcus faecalisis associated with host cell adherence and endocarditis. The Fsr quorum-sensing system of E. faecalis, a two-component signal transduction system, has also been repeatedly linked to virulence in E. faecalis, due in part to the transcriptional induction of an extracellular metalloprotease, gelatinase (GelE). In this study, we discovered that disruption of the Fsr pathway significantly increased the levels of Ace on the cell surface in the latter phases of growth. Furthermore, we observed that, in addition to fsrB mutants, other strains identified as deficient in GelE activity also demonstrated a similar phenotype. Additional experiments demonstrated the GelE-dependent cleavage of Ace from the surface of E. faecalis, confirming that GelE specifically reduces Ace cell surface display. In addition, disruption of the Fsr system or GelE expression significantly improved the ability of E. faecalis to adhere to collagen, which is consistent with higher levels of Ace on the E. faecalis surface. These results demonstrate that the display of Ace is mediated by quorum sensing through the action of GelE, providing insight into the complicated world of Gram-positive pathogen adhesion and colonization.

Adherence to host extracellular matrix and serum components by Enterococcus faecium isolates of diverse origin

Enterococcus faecium has emerged as an important cause of nosocomial infections over the last two decades. We recently demonstrated collagen type I (CI) as a common adherence target for some E. faecium isolates and a significant correlation was found to exist between acm-mediated CI adherence and clinical origin. Here, we evaluated 60 diverse E. faecium isolates for their adherence to up to 15 immobilized host extracellular matrix and serum components. Adherence phenotypes were most commonly observed to fibronectin (Fn) (20% of the 60 isolates), fibrinogen (17%) and laminin (Ln) (13%), while only one or two of the isolates adhered to collagen type V (CV), transferrin or lactoferrin and none to the other host components tested. Adherence to Fn and Ln was almost exclusively restricted to clinical isolates, especially the endocarditis-enriched nosocomial genogroup clonal complex 17 (CC17). Thus, the ability to adhere to Fn and Ln, in addition to CI, may have contributed to the emergence and adaptation of E. faecium, in particular CC17, as a nosocomial pathogen.

A family of fibrinogen-binding MSCRAMMs from Enterococcus faecalis

We report that three (EF0089, EF2505 and EF1896, renamed here Fss1, Fss2 and Fss3, respectively, for Enterococcus faecalis surface protein) of the recently predicted MSCRAMMs (microbial surface components recognizing adhesive matrix molecules) in E. faecalis strain V583 bind fibrinogen (Fg). Despite an absence of extensive primary sequence homology, the three proteins appear to be related structurally. Within the N-terminal regions of the three enterococcal proteins, we identified pairs of putative IgG-like modules with a high degree of predicted structural similarity to the Fg-binding N2 and N3 domains of the staphylococcal MSCRAMMs ClfA and SdrG. A second N2N3-like segment was predicted in Fss1. Far-UV circular dichroism spectroscopy revealed that all four predicted N2N3-like regions are composed mainly of beta-sheets with only a minor proportion of alpha-helices, which is characteristic of Ig-like folded domains. Three of the four identified enterococcal N2N3-like regions showed potent dose-dependent binding to Fg. However, the specificity of the Fg-binding MSCRAMMs differs, as indicated by far-Western blots, which showed that recombinant segments of the MSCRAMMs bound different Fg polypeptide chains. Enterococci grown in serum-supplemented broth adhere to Fg-coated surfaces, and inactivation in strain OG1RF of the gene encoding Fss2 resulted in reduced adherence, whilst complementation of the mutant restored full Fg adherence. Thus, E. faecalis contains a family of MSCRAMMs that structurally and functionally resemble the Fg-binding MSCRAMMs of staphylococci.

Dentinal tubule invasion and adherence by Enterococcus faecalis

AIM

To investigate dentinal tubule invasion and the predilection of Enterococcus faecalis for dentinal tubule walls.

METHODOLOGY

The invasion of dentinal tubules in extracted human teeth by E. faecalis was measured ex vivo after 8 weeks of incubation. The canal walls of 16 root sections were either intact or instrumented with or without smear layer present. Extent and maximum depth of tubule invasion were assessed histologically and compared between groups. In the adherence study, 44 vertically split root samples were prepared to expose longitudinally aligned dentinal tubules and fractured orthodentine (OD). Surfaces were exposed to E. faecalis (erythromycin resistant strain, JH2-2 carrying plasmid pGh9:ISS1) and incubated aerobically for 2 h. Samples were processed for analysis using scanning electron microscopy. Bacterial adhesion to tubule walls versus fractured OD was calculated as number of cells per 100 microm(2).

RESULTS

The strain of E. faecalis used in this study showed moderate to heavy tubule invasion after 8 weeks. In the adhesion studies, significantly more bacteria adhered to fractured OD than to dentinal tubule walls (ANOVA, P < 0.001). With respect to the tubule wall, adherence was greater in inner versus outer dentine (P = 0.02) and greater when bacterial adhesion was tested in chemically defined medium than in phosphate-buffered saline (ANOVA, P < 0.001).

CONCLUSIONS

Although E. faecalis readily invaded tubules, it did not adhere preferentially to tubule walls. Initial colonization of dentinal tubules by E. faecalis may depend primarily on other factors.

A functional collagen adhesin gene, acm, in clinical isolates of Enterococcus faecium correlates with the recent success of this emerging nosocomial pathogen

Enterococcus faecium recently evolved from a generally avirulent commensal into a multidrug-resistant health care-associated pathogen causing difficult-to-treat infections, but little is known about the factors responsible for this change. We previously showed that some E. faecium strains express a cell wall-anchored collagen adhesin, Acm. Here we analyzed 90 E. faecium isolates (99% acm(+)) and found that the Acm protein was detected predominantly in clinically derived isolates, while the acm gene was present as a transposon-interrupted pseudogene in 12 of 47 isolates of nonclinical origin. A highly significant association between clinical (versus fecal or food) origin and collagen adherence (P Collapse

Key Words Collapse

MESH Headings

• Adhesins, Bacterial/genetics
• Adhesins, Bacterial/metabolism
• Animals
• Antibodies, Bacterial/blood
• Bacterial Adhesion
• Bacterial Typing Techniques
• Cattle
• Chickens
• Cluster Analysis
• Collagen/metabolism
• Cross Infection/microbiology
• DNA Fingerprinting
• DNA Transposable Elements
• DNA, Bacterial/genetics
• Electrophoresis, Gel, Pulsed-Field
• Endocarditis, Bacterial/immunology
• Enterococcus faecium/classification
• Enterococcus faecium/genetics
• Enterococcus faecium/isolation & purification
• Enterococcus faecium/pathogenicity
• Feces/microbiology
• Food Microbiology
• Genes, Bacterial
• Genotype
• Gram-Positive Bacterial Infections/microbiology
• Humans
• Pseudogenes
• Sequence Analysis, DNA
• Swine
• Turkeys

Collapse

Grants

• R01 AI067861 NIAID NIH HHS
• UL1 RR024148 NCRR NIH HHS
• R01 AI 67861 NIAID NIH HHS

Collapse

Affiliation(s)

Sreedhar R Nallapareddy Department of Internal Medicine, Division of Infectious Diseases, Center for the Study of Emerging and Re-Emerging Pathogens, University of Texas Medical School, Houston, Texas 77030, USA
Kavindra V Singh
Pablo C Okhuysen
Barbara E Murray

Collapse

Role played by serum, a biological cue, in the adherence of Enterococcus faecalis to extracellular matrix proteins, collagen, fibrinogen, and fibronectin

BACKGROUND

Most previous studies have found that Enterococcus faecalis isolates do not show significant adherence to fibronectin and fibrinogen.

METHODS

The influence of various conditions on E. faecalis adherence to extracellular matrix (ECM) proteins was evaluated using a radiolabeled-cell adherence assay.

RESULTS

Among the conditions studied, growth in 40% horse serum (a biological cue with potential clinical relevance) elicited adherence of all 46 E. faecalis strains tested to fibronectin and fibrinogen but not to elastin; adherence levels were independent of strain source, and adherence was eliminated by treating cells with trypsin. As previously reported, serum also elicited adherence to collagen. Although prolonged exposure to serum during growth was needed for enhancement of adherence to fibrinogen, brief exposure (<5 min) to serum had an immediate, although partial, enhancing effect on adherence to fibronectin and, to a lesser extent, collagen; pretreatment of bacteria with chloramphenicol did not decrease this enhanced adherence to fibronectin and collagen, indicating that protein synthesis is not required for the latter effect.

CONCLUSION

Taken together, these data suggest that serum components may serve (1) as host environmental stimuli to induce the production of ECM protein-binding adhesin(s), as previously seen with collagen adherence, and also (2) as activators of adherence, perhaps by forming bridges between ECM proteins and adhesins.

Glycopeptide-resistant enterococci: deciphering virulence, resistance and epidemicity

PURPOSE OF REVIEW

Since their first discovery, glycopeptide-resistant enterococci have emerged as important nosocomial pathogens first in the US, followed by the rest of the world. In this review the most recent findings that relate to enterococcal epidemiology, virulence and glycopeptide-resistance maintenance will be discussed.

RECENT FINDINGS

Frequent horizontal gene transfer and recombination, resulting in high-level genome plasticity, facilitating rapid responsiveness of enterococci to changing environmental conditions may have contributed to the worldwide emergence. For Enterococcus faecium this has resulted in the development of a distinct genetic subspecies, clonal complex 17, responsible for the majority of glycopeptide-resistant enterococci-related hospital burden. Preliminary data also suggest that such high-risk enterococcal clonal complexes may exist within Enterococcus faecalis. The last 2 years have not only disclosed novel determinants implicated in enterococcal pathogenesis, but also showed that enterococci are able to sense their environment and regulate virulence gene expression accordingly. Linkage of glycopeptide resistance in enterococci to plasmid maintenance systems holds a doomed perspective for controlling antibiotic resistance emergence.

SUMMARY

Recent developments have improved our understanding of enterococcal population structure, pathogenesis and glycopeptide-resistance maintenance. This may contribute to the development of novel intervention strategies to prevent enterococcal infections and contain the spread of glycopeptide-resistant enterococci.

Monoclonal antibodies recognizing the Enterococcus faecalis collagen-binding MSCRAMM Ace: conditional expression and binding analysis

Enterococci are opportunistic pathogens known to cause numerous clinical infections and complications in humans. Adhesin-mediated binding to extracellular matrix (ECM) proteins of the host is thought to be a crucial step in the pathogenesis of these bacterial infections. Adhesin of collagen from Enterococcus faecalis (Ace) is a cell-wall anchored protein of E. faecalis that has been shown to be important for bacterial binding to the ECM. In this report, we characterize the conditions for Ace expression and demonstrate Ace binding to mammalian epithelial and endothelial cells as well as to collagens found in the ECM. To further characterize Ace expression and function, we report the generation of a panel of monoclonal antibodies (mAbs) directed against this important E. faecalis virulence factor. Through the use of multiple in vitro assays, surface plasmon resonance and flow cytometry, we have characterized this panel of mAbs which may prove to be not only beneficial in studies that address the precise biological role of adhesion of E. faecalis, but may also serve as beneficial therapeutic agents against E. faecalis infections.

Endocarditis and biofilm-associated pili of Enterococcus faecalis

Increasing multidrug resistance in Enterococcus faecalis, a nosocomial opportunist and common cause of bacterial endocarditis, emphasizes the need for alternative therapeutic approaches such as immunotherapy or immunoprophylaxis. In an earlier study, we demonstrated the presence of antibodies in E. faecalis endocarditis patient sera to recombinant forms of 9 E. faecalis cell wall-anchored proteins; of these, we have now characterized an in vivo-expressed locus of 3 genes and an associated sortase gene (encoding sortase C; SrtC). Here, using mutation analyses and complementation, we demonstrated that both the ebp (encoding endocarditis and biofilm-associated pili) operon and srtC are important for biofilm production of E. faecalis strain OG1RF. In addition, immunogold electron microscopy using antisera against EbpA-EbpC proteins as well as patient serum demonstrated that E. faecalis produces pleomorphic surface pili. Assembly of pili and their cell wall attachment appeared to occur via a mechanism of cross-linking of the Ebp proteins by the designated SrtC. Importantly, a nonpiliated, allelic replacement mutant was significantly attenuated in an endocarditis model. These biologically important surface pili, which are antigenic in humans during endocarditis and encoded by a ubiquitous E. faecalis operon, may be a useful immunotarget for studies aimed at prevention and/or treatment of this pathogen.

Ligand-signaled upregulation of Enterococcus faecalis ace transcription, a mechanism for modulating host-E. faecalis interaction

Enterococcus faecalis, the third most frequent cause of bacterial endocarditis, appears to be equipped with diverse surface-associated proteins showing structural-fold similarity to the immunoglobulin-fold family of staphylococcal adhesins. Among the putative E. faecalis surface proteins, the previously characterized adhesin Ace, which shows specific binding to collagen and laminin, was detectable in surface protein preparations only after growth at 46 degrees C, mirroring the finding that adherence was observed in 46 degrees C, but not 37 degrees C, grown E. faecalis cultures. To elucidate the influence of different growth and host parameters on ace expression, we investigated ace expression using E. faecalis OG1RF grown in routine laboratory media (brain heart infusion) and found that ace mRNA levels were low in all growth phases. However, quantitative reverse transcription-PCR showed 18-fold-higher ace mRNA amounts in cells grown in the presence of collagen type IV compared to the controls. Similarly, a marked increase was observed when cells were either grown in the presence of collagen type I or serum but not in the presence of fibrinogen or bovine serum albumin. The production of Ace after growth in the presence of collagen type IV was demonstrated by immunofluorescence microscopy, mirroring the increased ace mRNA levels. Furthermore, increased Ace expression correlated with increased collagen and laminin adhesion. Collagen-induced Ace expression was also seen in three of three other E. faecalis strains of diverse origins tested, and thus it appears to be a common phenomenon. The observation of host matrix signal-induced adherence of E. faecalis may have important implications on our understanding of this opportunistic pathogen.

Enterococcus faecalis Adhesin, Ace, Mediates Attachment to Particulate Dentin

An enzyme linked immunosorbent assay was developed to assess E. faecalis adhesion to particulate dentin. E. faecalis, OG1RF, which expresses the collagen binding protein (Ace+), and a derivative of OG1RF, TX5256, deficient in the collagen binding protein (Ace-) were grown at 46 degrees C, necessary for in vitro expression of Ace, and at 37 degrees C. E. faecalis binding to dentin was measured at 0, 15, 30, 60, 120, and 360 minutes. Compared to TX5256 and OG1RF grown at 37 degrees C, OG1RF grown at 46 degrees C adhered significantly better at all time points except 15 minutes (p < 0.001) exhibiting maximum binding at 120 minutes (17.4% of a positive control). Type I collagen at 100 microg/ml inhibited dentin binding by OG1RF grown at 46 degrees C in both competition (p < 0.005) and displacement assays (p < 0.046). Immunoaffinity purified anti-Ace IgG at 200 microg of protein inhibited adhesion of OG1RF grown at 46 degrees C to dentin.

Enterococcal prosthetic valve infective endocarditis: report of 45 episodes from the International Collaboration on Endocarditis-merged database

Enterococcal prosthetic valve infective endocarditis (PVE) is an incompletely understood disease. In the present study, patients with enterococcal PVE were compared to patients with enterococcal native valve endocarditis (NVE) and other types of PVE to determine differences in basic clinical characteristics and outcomes using a large multicenter, international database of patients with definite endocarditis. Forty-five of 159 (29%) cases of definite enterococcal endocarditis were PVE. Patients with enterococcal PVE were demographically similar to patients with enterococcal NVE but had more intracardiac abscesses (20% vs. 6%; p=0.009), fewer valve vegetations (51% vs. 79%; p<0.001), and fewer cases of new valvular regurgitation (12% vs. 45%; p=0.01). Patients with either enterococcal PVE or NVE were elderly (median age, 73 vs. 69; p=0.06). Rates of in-hospital mortality, surgical intervention, heart failure, peripheral embolization, and stroke were similar in both groups. Patients with enterococcal PVE were also demographically similar to patients with other types of PVE, but mortality may be lower (14% vs. 26%; p=0.08). Notably, 93% of patients with enterococcal PVE came from European centers, as compared with only 79% of patients with enterococcal NVE (p=0.03). Thus, patients with enterococcal PVE have higher rates of myocardial abscess formation and lower rates of new regurgitation compared to patients with enterococcal NVE, but there are no differences between the groups with regard to surgical or mortality rates. In contrast, though patients with enterococcal PVE and patients with other types of PVE share similar characteristics, mortality is higher in the latter group. Importantly, the prevalence of enterococcal PVE was higher in the European centers in this study.

Tissue-specific adherent Enterococcus faecalis strains that show highly efficient adhesion to human bladder carcinoma T24 cells also adhere to extracellular matrix proteins

The ability of Enterococcus faecalis clinical isolates to adhere to immobilized extracellular matrixes (ECMs) coating the walls of microtiter plates was examined by microscopy. The ECMs consisted of fibronectin, laminin, collagen types I, II, IV, and V, fibrinogen, and lactoferrin. With the exception of fibrinogen, each isolate showed a different level of adherence to each of the ECMs. No significant level of adherence to fibrinogen was observed for any isolate. The tissue-specific adhesive strains AS11, AS12, AS14, AS15, HT11, and HT12, which showed highly efficient adherence to human bladder carcinoma T24 cells and human bladder epithelial cells, showed strong adherence to fibronectin, laminin, and collagen type I, II, IV, and V ECMs, and the levels were greater than 10(4) cells/mm2 of well surface coated by ECM. None of the isolates that showed little adherence to human bladder carcinoma T24 cells showed efficient adherence to all the ECMs. The levels of adherence of gelatinase-producing isolates to the collagens were lower than the levels of adherence of gelatinase-negative isolates. When tissue-specific adhesive strains that adhered strongly to each ECM were preincubated with fibronectin, the adherence of the strains to fibronectin was inhibited, but the adherence of the strains to collagen type IV was not inhibited. Likewise, preincubation with collagen type IV inhibited adherence to collagen type IV but not adherence to fibronectin. All of the E. faecalis isolates were shown to carry the ace gene by PCR analysis performed with specific primers for collagen binding domain A of ace. The ace gene encodes Ace (adhesin of collagen from enterococci). The prtF gene of group A streptococci, which encodes the fibronectin binding protein of group A streptococci, was not detected in the tissue-specific adhesive strains by Southern analysis performed with the prtF probe of the Streptococcus pyogenes JRS4 strain. Mutants with altered collagen binding were isolated by insertion of Tn916 into the chromosome of tissue-specific adhesive strain AS14. The number of mutant adhesive bacterial cells that adhered to collagen and also to laminin was 1 or 2 orders lower than the number observed for the wild-type strain, but the level of adherence to fibronectin remained the same as that of the wild-type strain.

Virulence factors of Enterococcus faecalis: relationship to endodontic disease

Enterococcus faecalis is a micro-organism that can survive extreme challenges. Its pathogenicity ranges from life-threatening diseases in compromised individuals to less severe conditions, such as infection of obturated root canals with chronic apical periodontitis. In the latter situation, the infecting organisms are partly shielded from the defense mechanisms of the body. In this article, we review the virulence factors of E. faecalis that may be related to endodontic infection and the periradicular inflammatory response. The most-cited virulence factors are aggregation substance, surface adhesins, sex pheromones, lipoteichoic acid, extracellular superoxide production, the lytic enzymes gelatinase and hyaluronidase, and the toxin cytolysin. Each of them may be associated with various stages of an endodontic infection as well as with periapical inflammation. While some products of the bacterium may be directly linked to damage of the periradicular tissues, a large part of the tissue damage is probably mediated by the host response to the bacterium and its products.

A family of putative MSCRAMMs from Enterococcus faecalis

The recently published Enterococcus faecalis genome [Paulsen, I. T., Banerjei, L., Myers, G. S. & 29 other authors (2003). Science 299, 2071-2074)] was examined and 41 putative cell-wall-anchored proteins were identified. Seventeen of these proteins are predicted to contain tandemly repeated immunoglobulin-like folds characteristic of the structural organization of staphylococcal adhesins of the MSCRAMM (microbial surface component recognizing adhesive matrix molecules) type. Two of the nine proteins selected for further study appear to represent cell-wall-anchored enzymes. It is proposed that the remaining seven proteins constitute a family of structurally related proteins potentially interacting with proteins of the host. This family includes the previously identified collagen/laminin-binding MSCRAMM ACE [Rich, R. L., Kreikemeyer, B., Owens, R. T., LaBrenz, S., Narayana, S. V., Weinstock, G. M., Murray, B. E. & Hook, M. (1999). J Biol Chem 274, 26939-26945]. It is further demonstrated that genes encoding the seven putative MSCRAMMs are present in all E. faecalis strains tested and these proteins appear to be expressed during infection in humans, since sera from infected individuals contain antibodies reacting with recombinant versions of the enterococcal proteins.

An Enterococcus faecium secreted antigen, SagA, exhibits broad-spectrum binding to extracellular matrix proteins and appears essential for E. faecium growth

A gene encoding a major secreted antigen, SagA, was identified in Enterococcus faecium by screening an E. faecium genomic expression library with sera from patients with E. faecium-associated endocarditis. Recombinant SagA protein showed broad-spectrum binding to extracellular matrix (ECM) proteins, including fibrinogen, collagen type I, collagen type IV, fibronectin, and laminin. A fibrinogen-binding protein, purified from culture supernatants of an E. faecium clinical isolate, was found to match the N-terminal sequence of the predicted SagA protein and to react with the anti-SagA antibody, confirming that it was the SagA protein; this protein appeared as an 80- to 90-kDa smear on a Western blot that was sensitive to proteinase K and resistant to periodate treatment and glycoprotein staining. When overexpressed in E. faecium and Escherichia coli, the native and recombinant SagA proteins formed stable oligomers, apparently via their C-terminal domains. The SagA protein is composed of three domains: (i) a putative coiled-coil N-terminal domain that shows homology to the N-terminal domain of Streptococcus mutans SagA protein (42% similarity), previously shown to be involved in cell wall integrity and cell shape maintenance, and to the P45 protein of Listeria monocytogenes (41% similarity); (ii) a central domain containing direct repeats; and (iii) a C-terminal domain that is similar to that found in various proteins, including P45 (50% similarity) and P60 (52% similarity) of L. monocytogenes. The P45 and P60 proteins both have cell wall hydrolase activity, and the latter has also been shown to be involved in virulence, whereas cell wall hydrolase activity was not detected for SagA protein. The E. faecium sagA gene, like the S. mutans homologue, is located in a cluster of genes encoding proteins that appear to be involved in cell wall metabolism and could not be disrupted unless it was first transcomplemented, suggesting that the sagA gene is essential for E. faecium growth and may be involved in cell wall metabolism. In conclusion, the extracelluar E. faecium SagA protein is apparently essential for growth, shows broad-spectrum binding to ECM proteins, forms oligomers, and is antigenic during infection.

Identification of a Treponema pallidum laminin-binding protein

Host extracellular matrix (ECM) components represent ideal microbial adhesion targets that many pathogens use for colonization of tissues and initiation of infection. This study investigated the interaction of the spirochete Treponema pallidum with the ECM component laminin. To identify candidate laminin-binding adhesins, the T. pallidum genome was analyzed to predict open reading frames that encode putative outer membrane proteins, as these proteins interact directly with host ECM components. Subsequent recombinant expression of these proteins and analysis of their laminin-binding potential identified one protein, Tp0751, that demonstrated specific attachment to laminin. Tp0751 attached to laminin in a dose-dependent, saturable manner but did not attach to the ECM component collagen type I or IV or to the negative control proteins fetuin or bovine serum albumin. Sodium metaperiodate treatment of laminin reduced the Tp0751-laminin interaction in a concentration-dependent manner, suggesting that oligosaccharides play a role in this interaction. In addition, Tp0751-specific antibodies were detected in serum samples collected from both experimental and natural syphilis infections, indicating that Tp0751 is expressed in vivo during the course of infection. Collectively, these experiments identified Tp0751 as a laminin-binding protein that is expressed during infection and may be involved in attachment of T. pallidum to host tissues.

Clinical isolates of Enterococcus faecium exhibit strain-specific collagen binding mediated by Acm, a new member of the MSCRAMM family

A collagen-binding adhesin of Enterococcus faecium, Acm, was identified. Acm shows 62% similarity to the Staphylococcus aureus collagen adhesin Cna over the entire protein and is more similar to Cna (60% and 75% similarity with Cna A and B domains respectively) than to the Enterococcus faecalis collagen-binding adhesin, Ace, which shares homology with Acm only in the A domain. Despite the detection of acm in 32 out of 32 E. faecium isolates, only 11 of these (all clinical isolates, including four vancomycin-resistant endocarditis isolates and seven other isolates) exhibited binding to collagen type I (CI). Although acm from three CI-binding vancomycin-resistant E. faecium clinical isolates showed 100% identity, analysis of acm genes and their promoter regions from six non-CI-binding strains identified deletions or mutations that introduced stop codons and/or IS elements within the gene or the promoter region in five out of six strains, suggesting that the presence of an intact functional acm gene is necessary for binding of E. faecium strains to CI. Recombinant Acm A domain showed specific and concentration-dependent binding to collagen, and this protein competed with E. faecium binding to immobilized CI. Consistent with the adherence phenotype and sequence data, probing with Acm-specific IgGs purified from anti-recombinant Acm A polyclonal rabbit serum confirmed the surface expression of Acm in three out of three collagen-binding clinical isolates of E. faecium tested, but in none of the strains with a non-functional pseudo acm gene. Introduction of a functional acm gene into two non-CI-binding natural acm mutant strains conferred a CI-binding phenotype, further confirming that native Acm is sufficient for the binding of E. faecium to CI. These results demonstrate that acm, which encodes a potential virulence factor, is functional only in certain infection-derived clinical isolates of E. faecium, and suggest that Acm is the primary adhesin responsible for the ability of E. faecium to bind collagen.

Lectin-like binding and antibiotic sensitivity of enterococci from wild herbivores

Fifty eight enterococcal isolates from wild herbivores were tested for their antibiotic sensitivity pattern and lectin-like binding of extracellular matrix (ECM) and serum proteins. Kanamycin resistance was very frequent; many multiresistant strains were also isolated. All isolates were sensitive to rifampicin. Resistance to gentamicin, novobiocin, and tetracycline was widely distributed in the microflora of wild herbivores breeded in zoological garden in Kosice. No autoaggregating strains were detected among these 58 enterococcal isolates. Various degrees of binding of mucins, fetuin, heparin, fibrinogen, and fibronectin were observed in individual strains. However, bovine lactoferrin binding by enterococci from deers and chamoises was either negative (0) or strongly positive (3). With regard to influence of growth media, TH agar was found to be better for the expression of lectin-like binding than blood agar, TH broth and Nutrient broth. A significant effect (P < 0.001 or P < 0.05) of proteolytic treatment was observed in six selected strains. However, there is a difference between the effect of trypsin and pronase P. Pronase treatment more effectively decreased binding of some strains (1H, 6A, EF 1111, EC 1292), while trypsin treatment decreased more binding of other enterococcal strains (EF 953 and 1E). Significant (P < 0.001) influence of metaperiodate, which cleaves the C-C bond between vicinal groups of sugars, on collagen I binding by three selected strains (1E, 1H, 6A) and bovine lactoferrin binding (by EF 1111, EC 1292, EF 953) was also observed. However, its influence was very different. In two strains (1H and EC 1292), ECM binding was decreased, while in four other strains (1E, 6A, EF 1111, EF 953) it was increased.

Isolation of a putative laminin binding protein from Streptococcus anginosus

Viridans streptococci, including Streptococcus anginosus, are a common cause of infective endocarditis in humans. Adherence mechanisms involved in colonization of non-diseased native valves (present in 40% of native valve endocarditis) are unknown. We have previously shown that an endocarditis isolate of S. anginosus adheres to exposed basement membrane of human and porcine valve tissue in a laminin dependent manner. We now describe the partial purification of an 80 kDa putative laminin binding protein (PLBP) by biochemical methods. Amino acid sequence of PLBP peptides is similar to substrate binding proteins of ABC transporters in other Gram-positive cocci.

Streptococcus anginosus adheres to vascular endothelium basement membrane and purified extracellular matrix proteins

The mechanisms of bacterial adherence in the initial stages of native valve endocarditis are unclear, especially in patients without valve disease or the presence of a platelet-fibrin thrombus. Extracellular matrix may act as a ligand in areas of exposed basement membrane on the endothelial monolayer. In this study, adherence of 55 clinical blood and 21 oral viridans streptococcal isolates was examined using purified extracellular matrix compounds. The majority of blood and oral isolates exhibited adherence to purified laminin, fibronectin, and fibrinogen, with lesser adherence to type I and IV collagens. Adherence to laminin and fibronectin was concentration dependent, saturable, and competitively inhibited with soluble ligand. A Streptococcus anginosus isolate and other viridans strains exhibiting a strong laminin adherence phenotype bound extensively to the endothelial aspect of human and porcine valve tissue sections and were inhibited by soluble laminin and anti-laminin antibody fragments. Using a novel native porcine valve explant adherence model, we localized binding to areas of exposed basement membrane by confocal and scanning electron microscopy. These studies support the hypothesis that bacterial adherence to exposed basement membrane plays a role in the initial phase of native valve endocarditis.

Aggregation substance-mediated adherence of Enterococcus faecalis to immobilized extracellular matrix proteins

Aggregation substance (AS) of Enterococcus faecalis (E. faecalis), a sex pheromone plasmid encoded cell surface protein, mediates the formation of bacterial aggregates, thereby promoting plasmid transfer. The influence of pAD1-encoded AS, Asa1, on binding to immobilized extracellular matrix proteins was studied. The presence of AS increased enterococcal adherence to fibronectin more than eight-fold, to thrombospondin more than four-fold, to vitronectin more than three-fold, and to collagen type I more than two-fold (P<0.001). In contrast, binding to laminin and collagen type IV occurred independently of AS. Adherence of the constitutively AS expressing E. faecalis OG1X(pAM721) to immobilized fibronectin was found to be approximately five times higher than that of Staphylococcus aureus Cowan and approximately 30 times higher than that of Streptococcus bovis. Investigation of strains with various deletions within the structural gene of asa1 suggests that attachment to immobilized fibronectin is mainly mediated by amino acids within the variable region or by neighbouring residues. Thus, AS may promote adherence to injured epithelium and endothelium, where extracellular matrix proteins are exposed, thereby facilitating colonization and infection.

Monoclonal antibodies to CNA, a collagen-binding microbial surface component recognizing adhesive matrix molecules, detach Staphylococcus aureus from a collagen substrate

Previous studies showed that Staphylococcus aureus expresses a collagen-binding MSCRAMM (Microbial Surface Component Recognizing Adhesive Matrix Molecules), CNA, that is necessary and sufficient for S. aureus cells to adhere to cartilage and is a virulence factor in experimental septic arthritis. We have now used a monoclonal antibody (mAb) approach to further analyze the structure and function of CNA. 22 mAbs raised against the minimal ligand binding domain, CNA-(151-318), were shown to bind to the MSCRAMM with similar affinity. All mAbs appear to recognize conformation-dependent epitopes that were mapped throughout the CNA-(151-318) domain using a chimeric strategy where segments of CNA are grafted on ACE, a structurally related MSCRAMM from Enterococcus faecalis. These mAbs were able to inhibit (125)I-collagen binding to CNA-(151-318) as well as to intact S. aureus cells. They also interfered with the attachment of bacteria to collagen substrates. Furthermore, some of the mAbs could effectively displace (125)I-collagen bound to the bacteria. These displacing mAbs were also able to detach bacteria that had adhered to a collagen substrate in a preincubation, raising the possibility that some of the mAbs may be used as therapeutic agents.

Enterococcus faecalis adhesin, ace, mediates attachment to extracellular matrix proteins collagen type IV and laminin as well as collagen type I

Adhesin-mediated binding to extracellular matrix (ECM) proteins is thought to be a crucial step in the pathogenic process of many bacterial infections. We have previously reported conditional adherence of most Enterococcus faecalis isolates, after growth at 46 degrees C, to ECM proteins collagen types I and IV and laminin; identified an E. faecalis-specific gene, ace, whose encoded protein has characteristics of a bacterial adhesin; and implicated Ace in binding to collagen type I. In this study, we constructed an ace disruption mutant from E. faecalis strain OG1RF that showed marked reduction in adherence to collagen types I and IV and laminin when compared to the parental OG1RF strain after growth at 46 degrees C. Polyclonal immune serum raised against the OG1RF-derived recombinant Ace A domain reacted with a single approximately 105-kDa band of mutanolysin extracts from OG1RF grown at 46 degrees C, while no band was detected in extracts from OG1RF grown at 37 degrees C, nor from the OG1RF ace mutant grown at 37 or 46 degrees C. IgGs purified from the anti-Ace A immune serum inhibited adherence of 46 degrees C-grown E. faecalis OG1RF to immobilized collagen type IV and laminin as well as collagen type I, at a concentration as low as 1 microg/ml, and also inhibited the 46 degrees C-evoked adherence of two clinical isolates tested. We also showed in vitro interaction of collagen type IV with Ace from OG1RF mutanolysin extracts on a far-Western blot. Binding of recombinant Ace A to immobilized collagen types I and IV and laminin was demonstrated in an enzyme-linked immunosorbent assay and was shown to be concentration dependent. These results indicate that Ace A mediates the conditional binding of E. faecalis OG1RF to collagen type IV and laminin in addition to collagen type I.

Diversity of ace, a gene encoding a microbial surface component recognizing adhesive matrix molecules, from different strains of Enterococcus faecalis and evidence for production of ace during human infections

Our previous work reported that most Enterococcus faecalis strains adhered to the extracellular matrix proteins collagen types I and IV and laminin after growth at 46 degrees C, but not 37 degrees C, and we subsequently identified an E. faecalis sequence, ace, that encodes a bacterial adhesin similar to the collagen binding protein Cna of Staphylococcus aureus. In this study, we examined the diversity of E. faecalis-specific ace gene sequences among different isolates obtained from various geographic regions as well as from various clinical sources. A comparison of nucleotide and deduced amino acid sequences of Ace from nine E. faecalis strains identified a highly conserved N-terminal A domain, followed by a variable B domain which contains two to five repeats of 47 amino acids in tandem array, preceded by a 20-amino-acid partial repeat. Using 17 other strains collected worldwide, the 5' region of ace that encodes the A domain was sequenced, and these sequences showed > or =97.5% identity. Among the previously reported five amino acids critical for collagen binding by Cna of S. aureus, four were found to be identical in Ace from all strains tested. Polyclonal immune rabbit serum prepared against recombinant Ace A derived from E. faecalis strain OG1RF detected Ace in mutanolysin extracts of seven of nine E. faecalis strains after growth at 46 degrees C; Ace was detected in four different molecular sizes that correspond to the variation in the B repeat region. To determine if there was any evidence to indicate that Ace might be produced under physiological conditions, we quantitatively assayed sera collected from patients with enterococcal infections for the presence of anti-Ace A antibodies. Ninety percent of sera (19 of 21) from patients with E. faecalis endocarditis showed reactivity with titers from 1:32 to >1:1,024; the only 2 sera which lacked antibodies to Ace A had considerably lower titers of antibodies to other E. faecalis antigens as well. Human-derived, anti-Ace A immunoglobulins G purified from an E. faecalis endocarditis patient serum inhibited adherence of 46 degrees C-grown E. faecalis OG1RF to collagen types I and IV and laminin. In conclusion, these results show that ace is highly conserved among isolates of E. faecalis, with at least four variants related to the differences in the B domain, is expressed by different strains during infection in humans, and human-derived antibodies can block adherence to these extracellular matrix proteins.

Ace is a collagen-binding MSCRAMM from Enterococcus faecalis

A putative collagen-binding MSCRAMM, Ace, of Enterococcus faecalis was identified by searching bacterial genome data bases for proteins containing domains homologous to the ligand-binding region of Cna, the collagen-binding MSCRAMM from Staphylococcus aureus. Ace was predicted to have a molecular mass of 71 kDa and contains features characteristic of cell surface proteins on Gram-positive bacteria, including a LPXTG motif for cross-linking to the cell wall. The N-terminal region of Ace contained a region (residues 174-319) in which 56% of the residues are identical or similar when compared with the minimal ligand-binding region of Cna (Cna 151-318); the remainder of the Ace A domain has 46% similarity with the corresponding region of the Cna A domain. Antibodies raised against recombinant Ace A domain were used to verify the cell surface expression of Ace on E. faecalis. These antibodies also effectively inhibited the adhesion of enterococcal cells to a collagen substrate, suggesting that Ace is a functional collagen-binding MSCRAMM. Structural modeling of the conserved region in Ace (residues 174-319) suggested a structure very similar to that reported for residues 151-318 of the Cna collagen-binding domain in which the ligand-binding site was identified as a trench transversing a beta-sheet face (Symersky, J., Patti, J. M., Carson, M., House-Pompeo, K., Teale, M., Moore, D., Jin, L., DeLucas, L. J., Höök, M., and Narayana, S. V. L. (1997) Nat. Struct. Biol. 10, 833-838). Biochemical analyses of recombinant Ace and Cna A domains supported the modeling data in that the secondary structures were similar as determined by CD spectroscopy and both proteins bound at multiple sites in type I collagen with micromolar affinities, but with different apparent kinetics. We conclude that Ace is a collagen-binding MSCRAMM on enterococci and is structurally and functionally related to the staphylococcal Cna protein.