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

Insights into ecology, pathogenesis, and biofilm formation of Enterococcus faecalis from functional genomics

SUMMARYEnterococcus faecalis is a significant resident of the gastrointestinal tract of most animals, including humans. Although generally non-pathogenic in healthy hosts, this microbe is adept at the exploitation of compromises in host immune functions, resulting in life-threatening opportunistic infections whose treatments are complicated by a high degree of intrinsic and acquired resistance to antimicrobial chemotherapy. Historically, progress in enterococcal research was limited by a lack of experimental models that replicate natural infection pathways and the relevance of in vitro studies to the natural biology of the organism. In this review, we summarize the history of enterococcal research during the 20th and early 21st centuries and describe more recent genetic and genomic tools and screens developed to address challenges in the field. We also describe how the results of recent studies reveal the importance of previously uncharacterized enterococcal genes, and we provide examples of interesting determinants that have emerged as important contributors to enterococcal biology. These factors may also serve as targets for future vaccines and chemotherapeutic agents to combat life-threatening hospital infections.

Antibacterial biofilm efficacy of calcium hydroxide loaded on Gum Arabic nanocarrier: an in-vitro study

BACKGROUND

An innovative intracanal medication formulation was introduced in the current study to improve the calcium hydroxide (Ca(OH)2) therapeutic capability against resistant Enterococcus faecalis (E. faecalis) biofilm. This in-vitro study aimed to prepare, characterize, and evaluate the antibacterial efficiency of Ca(OH)2 loaded on Gum Arabic (GA) nanocarrier (Ca(OH)2-GA NPs) and to compare this efficiency with conventional Ca(OH)2, Ca(OH)2 nanoparticles (NPs), GA, and GA NPs.

MATERIALS AND METHODS

The prepared nanoparticle formulations for the tested medications were characterized using Transmission Electron Microscope (TEM) and Fourier-Transform Infrared Spectroscopy (FTIR). 141 human mandibular premolars were selected, and their root canals were prepared. Twenty-one roots were then sectioned into 42 tooth slices. All prepared root canals (n = 120) and teeth slices (n = 42) were divided into six groups according to the intracanal medication used. E. faecalis was inoculated in the samples for 21 days to form biofilms, and then the corresponding medications were applied for 7 days. After medication application, the residual E. faecalis bacteria were assessed using CFU, Q-PCR, and SEM. Additionally, the effect of Ca(OH)2-GA NPs on E. faecalis biofilm genes (agg, ace, and efaA) was investigated using RT-PCR. Data were statistically analyzed at a 0.05 level of significance.

RESULTS

The synthesis of NPs was confirmed using TEM. The results of the FTIR proved that the Ca(OH)2 was successfully encapsulated in the GA NPs. Ca(OH)2-GA NPs caused a significant reduction in the E. faecalis biofilm gene expression when compared to the control (p < 0.001). There were significant differences in the E. faecalis CFU mean count and CT mean values between the tested groups (p < 0.001) except between the Ca(OH)2 and GA CFU mean count. Ca(OH)2-GA NPs showed the least statistical E. faecalis mean count among other groups. SEM observation showed that E. faecalis biofilm was diminished in all treatment groups, especially in the Ca(OH)2-GA NPS group when compared to the control group.

CONCLUSIONS

Ca(OH)2 and GA nanoparticles demonstrate superior anti-E. faecalis activity when compared to their conventional counterparts. Ca(OH)2-GA NPs showed the best antibacterial efficacy in treating E. faecalis biofilm. The tested NP formulations could be considered as promising intracanal medications.

Evaluation of Enterococcal Probiotic Usage and Review of Potential Health Benefits, Safety, and Risk of Antibiotic-Resistant Strain Emergence

Enterococci are often used in probiotics but can also cause nosocomial infections. As such, enterococcal consumption may have beneficial health effects, but a thorough evaluation of virulence absence and risk of antibiotic resistance spread is needed at the strain level. This article reviewed ten online health product shopping websites in the US. On these websites, 23 probiotic products using enterococci were found across 12 companies. In addition, this article reviewed studies that demonstrated the probiotic potential of enterococcal consumption (e.g., gastrointestinal and respiratory disease, hyperlipidemia alleviation, as well as infection prevention). To investigate the safety aspects of enterococci, the present work examined studies evaluating virulence factors and antibiotic resistance. Furthermore, this article assessed research that explored these virulent factors, specifically in probiotics containing enterococci, as well as the potential transfer mechanism of their antibiotic resistance. Based on reviewed data, enterococcal probiotic consumption has been proven beneficial for conditions or symptoms of multiple diseases without any apparent adverse effects. However, due to the plasmid- or transposon-mediated gene transfer ability of enterococci, surveillance monitoring and further studies regarding enterococcal consumption are warranted. Future studies that identify enterococcal strains safe to use in probiotics without virulence factors and antibiotic resistance are imperative for evidence-based decisions by health organizations and government agencies.

Current Trends of Enterococci in Dairy Products: A Comprehensive Review of Their Multiple Roles

As a genus that has evolved for resistance against adverse environmental factors and that readily exchanges genetic elements, enterococci are well adapted to the cheese environment and may reach high numbers in artisanal cheeses. Their metabolites impact cheese flavor, texture, and rheological properties, thus contributing to the development of its typical sensorial properties. Due to their antimicrobial activity, enterococci modulate the cheese microbiota, stimulate autolysis of other lactic acid bacteria (LAB), control pathogens and deterioration microorganisms, and may offer beneficial effects to the health of their hosts. They could in principle be employed as adjunct/protective/probiotic cultures; however, due to their propensity to acquire genetic determinants of virulence and antibiotic resistance, together with the opportunistic character of some of its members, this genus does not possess Qualified Presumption of Safety (QPS) status. It is, however, noteworthy that some putative virulence factors described in foodborne enterococci may simply reflect adaptation to the food environment and to the human host as commensal. Further research is needed to help distinguish friend from foe among enterococci, eventually enabling exploitation of the beneficial aspects of specific cheese-associated strains. This review aims at discussing both beneficial and deleterious roles played by enterococci in artisanal cheeses, while highlighting the need for further research on such a remarkably hardy genus.

Involvement of Chromosomally Encoded Homologs of the RRNPP Protein Family in Enterococcus faecalis Biofilm Formation and Urinary Tract Infection Pathogenesis

Enterococcus faecalis is an opportunistic pathogen capable of causing infections, including endocarditis and urinary tract infections (UTI). One of the well-characterized quorum-sensing pathways in E. faecalis involves coordination of the conjugal transfer of pheromone-responsive plasmids by PrgX, a member of the RRNPP protein family. Members of this protein family in various Firmicutes have also been shown to contribute to numerous cellular processes, including sporulation, competence, conjugation, nutrient sensing, biofilm formation, and virulence. As PrgX is a plasmid-encoded RRNPP family member, we surveyed the genome of the multidrug-resistant strain V583 for additional RRNPP homologs using computational searches and refined those identified hits for predicted structural similarities to known RRNPP family members. This led us to investigate the contribution of the chromosomally encoded RRNPP homologs to biofilm processes and pathogenesis in a catheter-associated urinary tract infection (CAUTI) model. In this study, we identified five such homologs and report that 3 of the 5 homologs, EF0073, EF1599, and EF1316, affect biofilm formation as well as outcomes in the CAUTI model.IMPORTANCE Enterococcus faecalis causes health care-associated infections and displays resistance to a variety of broad-spectrum antibiotics by acquisition of resistance traits as well as the ability to form biofilms. Even though a growing number of factors related to biofilm formation have been identified, mechanisms that contribute to biofilm formation are still largely unknown. Members of the RRNPP protein family regulate a diverse set of biological reactions in low-G+C Gram-positive bacteria (Firmicutes). Here, we identify three predicted structural homologs of the RRNPP family, EF0073, EF1599, and EF1316, which affect biofilm formation and CAUTI pathogenesis.

Pathogenicity of Enterococci

Enterococci are unusually well adapted for survival and persistence in a variety of adverse environments, including on inanimate surfaces in the hospital environment and at sites of infection. This intrinsic ruggedness undoubtedly played a role in providing opportunities for enterococci to interact with other overtly drug-resistant microbes and acquire additional resistances on mobile elements. The rapid rise of antimicrobial resistance among hospital-adapted enterococci has rendered hospital-acquired infections a leading therapeutic challenge. With about a quarter of a genome of additional DNA conveyed by mobile elements, there are undoubtedly many more properties that have been acquired that help enterococci persist and spread in the hospital setting and cause diseases that have yet to be defined. Much remains to be learned about these ancient and rugged microbes, particularly in the area of pathogenic mechanisms involved with human diseases.

Evaluation of Phage Therapy in the Context of Enterococcus faecalis and Its Associated Diseases

Bacteriophages (phages) or bacterial viruses have been proposed as natural antimicrobial agents to fight against antibiotic-resistant bacteria associated with human infections. Enterococcus faecalis is a gut commensal, which is occasionally found in the mouth and vaginal tract, and does not usually cause clinical problems. However, it can spread to other areas of the body and cause life-threatening infections, such as septicemia, endocarditis, or meningitis, in immunocompromised hosts. Although E. faecalis phage cocktails are not commercially available within the EU or USA, there is an accumulated evidence from in vitro and in vivo studies that have shown phage efficacy, which supports the idea of applying phage therapy to overcome infections associated with E. faecalis. In this review, we discuss the potency of bacteriophages in controlling E. faecalis, in both in vitro and in vivo scenarios. E. faecalis associated bacteriophages were compared at the genome level and an attempt was made to categorize phages with respect to their suitability for therapeutic application, using orthocluster analysis. In addition, E. faecalis phages have been examined for the presence of antibiotic-resistant genes, to ensure their safe use in clinical conditions. Finally, the domain architecture of E. faecalis phage-encoded endolysins are discussed.

Anti-Ace monoclonal antibody reduces Enterococcus faecalis aortic valve infection in a rat infective endocarditis model

Ace (Adhesin to collagen from Enterococcus faecalis) is a cell-wall anchored protein that is expressed conditionally and is important for virulence in a rat infective endocarditis (IE) model. Previously, we showed that rats immunized with the collagen binding domain of Ace (domain A), or administered anti-Ace domain A polyclonal antibody, were less susceptible to E. faecalis endocarditis than sham-immunized controls. In this work, we demonstrated that a sub nanomolar monoclonal antibody (mAb), anti-Ace mAb70, significantly diminished E. faecalis binding to ECM collagen IV in in vitro adherence assays and that, in the endocarditis model, anti-Ace mAb70 pre-treatment significantly reduced E. faecalis infection of aortic valves. The effectiveness of anti-Ace mAb against IE in the rat model suggests it might serve as a beneficial agent for passive protection against E. faecalis infections.

Expression of Adhesive Pili and the Collagen-Binding Adhesin Ace Is Activated by ArgR Family Transcription Factors in Enterococcus faecalis

It was shown previously that the disruption of the ahrC gene encoding a predicted ArgR family transcription factor results in a severe defect in biofilm formation in vitro, as well as a significant attenuation of virulence of Enterococcus faecalis strain OG1RF in multiple experimental infection models. Using transcriptome sequencing (RNA-seq), we observed ahrC-dependent changes in the expression of more than 20 genes. AhrC-repressed genes included predicted determinants of arginine catabolism and several other metabolic genes and predicted transporters, while AhrC-activated genes included determinants involved in the production of surface protein adhesins. Most notably, the structural and regulatory genes of the ebp locus encoding adhesive pili were positively regulated, as well as the ace gene, encoding a collagen-binding adhesin. Using lacZ transcription reporter fusions, we determined that ahrC and a second argR transcription factor gene, argR2, both function to activate the expression of ebpR, which directly activates the transcription of the pilus structural genes. Our data suggest that in the wild-type E. faecalis, the low levels of EbpR limit the expression of pili and that biofilm biomass is also limited by the amount of pili expressed by the bacteria. The expression of ace is similarly enhanced by AhrC and ArgR2, but ace expression is not dependent on EbpR. Our results demonstrate the existence of novel regulatory cascades controlled by a pair of ArgR family transcription factors that might function as a heteromeric protein complex.IMPORTANCE Cell surface adhesins play critical roles in the formation of biofilms, host colonization, and the pathogenesis of opportunistic infections by Enterococcus faecalis Here, we present new results showing that the expression of two major enterococcal surface adhesins, ebp pili, and the collagen-binding protein Ace is positively regulated at the transcription level by two argR family transcription factors, AhrC and ArgR2. In the case of pili, the direct target of regulation is the ebpR gene, previously shown to activate the transcription of the pilus structural genes, while the activation of ace transcription appears to be directly impacted by the two ArgR proteins. These transcription factors may represent new targets for blocking enterococcal infections.

Root Canal Microflora

Modern day endodontics is undergoing a massive change with the introduction of new molecular based techniques for microbial identification. This review focuses on the microbiota in untreated and root-filled canals. It will also describe briefly the recent developments in microbial identification and the mechanisms by which certain species of microbes are able to invade and establish themselves in the root canal.

The Enterococcus faecalis virulence factor ElrA interacts with the human Four-and-a-Half LIM Domains Protein 2

The commensal bacterium Enterococcus faecalis is a common cause of nosocomial infections worldwide. The increasing prevalence of multi-antibiotic resistant E. faecalis strains reinforces this public health concern. Despite numerous studies highlighting several pathology-related genetic traits, the molecular mechanisms of E. faecalis virulence remain poorly understood. In this work, we studied 23 bacterial proteins that could be considered as virulence factors or involved in the Enterococcus interaction with the host. We systematically tested their interactions with human proteins using the Human ORFeome library, a set of 12,212 human ORFs, in yeast. Among the thousands of tested interactions, one involving the E. faecalis virulence factor ElrA and the human protein FHL2 was evidenced by yeast two-hybrid and biochemically confirmed. Further molecular characterizations allowed defining an FHL2-interacting domain (FID) of ElrA. Deletion of the FID led to an attenuated in vivo phenotype of the mutated strain clearly indicating that this interaction is likely to contribute to the multifactorial virulence of this opportunistic pathogen. Altogether, our results show that FHL2 is the first host cellular protein directly targeted by an E. faecalis virulence factor and that this interaction is involved in Enterococcus pathogenicity.

[Pathogenicity of Enterococci]

Enterococci belong to the group of lactic acid bacteria (LAB), and inhabit the gastrointestinal tracts of a wide variety of animals from insects and to human, and the commensal organism in humans and animals. The commensal/probiotic role of enterococci has evolved through thousands of years in mutual coexistence. Enterococcus have many favorable traits that have been appreciated in food fermentation and preservation, and many serve as probiotics to promote health. While lactobacillus have been shown to confer numerous benefits on and often regarded as health bringing organisms, enterococci have become more recognized as emerging human pathogens in recent years. Mac Callum and Hastings characterized an organism, now known to be Enterococcal faecalis, which was isolated from a lethal case of endocarditis on 1899. The report was the first detailed description of its pathogenic capabilities. Over the past few decades, multi-drug resistance enterococci have become as important health-care associated pathogen, and leading causes of drug resistance infection. The modern life style including the broad use of antibiotics in medical practice and animal husbandry have selected for the convergence of potential virulence factors to the specific enterococcus species such as E. faecium and E. faecalis. The development of modern medical care of intensive and invasive medical therapies and treatments for human disease, and existence of severe compromised patients in hospitals has contributed to the increased prevalence of these opportunistic organisms. The virulence factors converged in E. faecalis and E. faecium which have been isolated in nosocomial infections, include antibiotic resistance, extracellular proteins (toxins), extrachromosome and mobile genetic elements, cell wall components, biofilm formation, adherence factors, and colonization factor such as bacteriocin, etc. In these potential virulence factors, I presented characteristics of enterococcal conjugative plasmid, cytolysin, collagen binding protein of adhesion, bacteriocins, and drug resistances. I made reference to our original reports, and review books for this review. The review books are "Enterococci: from Commensals to Leading Causes of Drug Resistant Infection, NCBI Bookshelf. A service of the National Library of Medicine, National Institute of Health. Ed. by Michael S Gilmore, Don B Clewell, Yasuyoshi Ike, and Nathan Shankar", and "The Enterococci: Pathogenesis, Molecular Biology, and Antibiotic Resistance, Gilmore M., Clewell D., Courvadin P., Dunny G., Murray B., Rice L., (ed) 2002. ASM Press".

Indomethacin injury to the rat small intestine is dependent upon biliary secretion and is associated with overgrowth of enterococci

NSAIDuse is limited due to the drugs' toxicity to the gastrointestinal mucosa, an action incompletely understood. Lower gut injury induced byNSAIDs is dependent on bile secretion and is reported to increase the growth of a number of bacterial species, including an enterococcal species,Enterococcus faecalis This study examined the relationships between indomethacin (INDO)-induced intestinal injury/bleeding, small bowel overgrowth (SBO) and dissemination of enterococci, and the contribution of bile secretion to these pathological responses. Rats received either a sham operation (SO) or bile duct ligation (BDL) prior to administration of two daily subcutaneous doses of saline orINDO, and 24 h later, biopsies of ileum and liver were collected for plating on selective bacterial media. Fecal hemoglobin (Hb) and blood hematocrit (Hct) were measured to assess intestinal bleeding. Of the four treatment groups, onlySO/INDOrats experienced a significant 10- to 30-fold increase in fecal Hb and reduction in Hct, indicating thatBDLattenuatedINDO-induced intestinal injury/bleeding. Ileal enterococcal colony-forming units were significantly increased (500- to 1000-fold) inSO/INDOrats. Of all groups, only theSO/INDOrats demonstrated gut injury, and this was associated with enterococcal overgrowth of the gut and dissemination to the liver. We also demonstrated thatINDO-induced intestinal injury andE. faecalisovergrowth was independent of the route of administration of the drug, as similar findings were observed in rats orally dosed with theNSAID Bile secretion plays an important role inINDO-induced gut injury and appears to support enterococcal overgrowth of the intestine.NSAID-induced enterococcalSBOmay be involved either as a compensatory response to gut injury or with the pathogenic process itself and the subsequent development of sepsis.

Genome-based characterization of hospital-adapted Enterococcus faecalis lineages

Vancomycin-resistant Enterococcus faecalis (VREfs) is an important nosocomial pathogen1,2. We undertook whole genome sequencing of E. faecalis associated with bloodstream infection in the UK and Ireland over more than a decade to determine the population structure and genetic associations with hospital adaptation. Three lineages predominated in the population, two of which (L1 and L2) were nationally distributed, and one (L3) geographically restricted. Genome comparison with a global collection identified that L1 and L3 were also present in the USA, but were genetically distinct. Over 90% of VREfs belonged to L1-L3, with resistance acquired and lost multiple times in L1 and L2, but only once followed by clonal expansion in L3. Putative virulence and antibiotic resistance genes were over-represented in L1, L2 and L3 isolates combined, versus the remainder. Each of the three main lineages contained a mixture of vancomycin-resistant and -susceptible E. faecalis (VSEfs), which has important implications for infection control and antibiotic stewardship.

The fibronectin-binding protein EfbA contributes to pathogenesis and protects against infective endocarditis caused by Enterococcus faecalis

EfbA is a PavA-like fibronectin adhesin of Enterococcus faecalis previously shown to be important in experimental urinary tract infection. Here, we expressed and purified the E. faecalis OG1RF EfbA and confirmed that this protein binds with high affinity to immobilized fibronectin, collagen I, and collagen V. We constructed an efbA deletion mutant and demonstrated that its virulence was significantly attenuated (P < 0.0006) versus the wild type in a mixed inoculum rat endocarditis model. Furthermore, efbA deletion resulted in diminished ability to bind fibronectin (P < 0.0001) and reduced biofilm (P < 0.001). Reintroduction of efbA into the original chromosomal location restored virulence, adherence to fibronectin, and biofilm formation to wild-type levels. Finally, vaccination of rats with purified recombinant EfbA protein protected against OG1RF endocarditis (P = 0.008 versus control). Taken together, our results demonstrate that EfbA is an important factor involved in E. faecalis endocarditis and that rEfbA immunization is effective in preventing such infection, likely by interfering with bacterial adherence.

The two-component system GrvRS (EtaRS) regulates ace expression in Enterococcus faecalis OG1RF

Expression of ace (adhesin to collagen of Enterococcus faecalis), encoding a virulence factor in endocarditis and urinary tract infection models, has been shown to increase under certain conditions, such as in the presence of serum, bile salts, urine, and collagen and at 46 °C. However, the mechanism of ace/Ace regulation under different conditions is still unknown. In this study, we identified a two-component regulatory system GrvRS as the main regulator of ace expression under these stress conditions. Using Northern hybridization and β-galactosidase assays of an ace promoter-lacZ fusion, we found transcription of ace to be virtually absent in a grvR deletion mutant under the conditions that increase ace expression in wild-type OG1RF and in the complemented strain. Moreover, a grvR mutant revealed decreased collagen binding and biofilm formation as well as attenuation in a murine urinary tract infection model. Here we show that GrvR plays a major role in control of ace expression and E. faecalis virulence.

Friend turned foe: evolution of enterococcal virulence and antibiotic resistance

The enterococci are an ancient genus that evolved along with the tree of life. These intrinsically rugged bacteria are highly adapted members of the intestinal consortia of a range of hosts that spans the animal kingdom. Enterococci are also leading opportunistic hospital pathogens, causing infections that are often resistant to treatment with most antibiotics. Despite the importance of enterococci as hospital pathogens, the vast majority live outside of humans, and nearly all of their evolutionary history took place before the appearance of modern humans. Because hospital infections represent evolutionary end points, traits that exacerbate human infection are unlikely to have evolved for that purpose. However, clusters of traits have converged in specific lineages that are well adapted to colonize the antibiotic-perturbed gastrointestinal tracts of patients and that thrive in the hospital environment. Here we discuss these traits in an evolutionary context, as well as how comparative genomics is providing new insights into the evolution of the enterococci.

Evaluation of the presence of Enterococcus Faecalis in root cementum: A confocal laser scanning microscope analysis

Aim:

The aim of this study is to address the cause of persistent infection of root cementum by Enterococcus faecalis.

Materials and Methods:

A sample of 60 human single-rooted teeth were divided into three groups. Group I (control group) had no access opening and one-third of the apical root cementum was sealed using varnish. Group II had no preparation of teeth samples. In group III, apical root cementum was exposed to organic acid and roughened using diamond point to mimic apical resorption. After access opening in groups II and III, all teeth samples were sterilized using gamma irradiation (25 kGy). E. faecalis broth was placed in the root canal and apical one-third of the tooth was immersed in the broth for 8 weeks with alternate day refreshment followed by biomechanical preparation, obturation and coronal seal. Apical one-third of all teeth samples were again immersed in the broth for 8 weeks with alternate day refreshment to mimic secondary infection. The samples were observed under a confocal microscope after splitting the teeth into two halves.

Results:

E. faecalis penetrated 160 μm deep into the root cementum in group III samples and only showed adhesion in group II samples.

Conclusion:

Penetration and survival of E. faecalis deep inside the cementum in extreme conditions could be the reason for persistent infection.

Enterococcus infection biology: lessons from invertebrate host models

The enterococci are commensals of the gastrointestinal tract of many metazoans, from insects to humans. While they normally do not cause disease in the intestine, they can become pathogenic when they infect sites outside of the gut. Recently, the enterococci have become important nosocomial pathogens, with the majority of human enterococcal infections caused by two species, Enterococcus faecalis and Enterococcus faecium. Studies using invertebrate infection models have revealed insights into the biology of enterococcal infections, as well as general principles underlying host innate immune defense. This review highlights recent findings on Enterococcus infection biology from two invertebrate infection models, the greater wax moth Galleria mellonella and the free-living bacteriovorous nematode Caenorhabditis elegans.

The majority of a collection of U.S. endocarditis Enterococcus faecalis isolates obtained from 1974 to 2004 lack capsular genes and belong to diverse, non-hospital-associated lineages

Eighty-one endocarditis-derived Enterococcus faecalis isolates that were collected from individual patients in the United States between 1974 and 2004 were sequence typed and analyzed for the presence of various genes, including some previously associated with virulence. Overall, using our previously described trilocus sequence typing (TLST), 44 different sequence types (STs) were found within this collection; 26 isolates were singletons (a unique TLST sequence type [ST(T)]), some ST(T)s contained multiple isolates (up to 6 isolates), and 16% of the isolates (13 isolates) could be grouped by additional sequence typing into clonal cluster 21 (CC21). Of note, only four isolates (7%) of the 56 whose multilocus sequence types were determined were found to belong to one of the previously described hospital-associated clonal clusters CC2 and CC9, and only 15% and 37% of all isolates had high-level resistance to gentamicin and streptomycin, respectively, including 10% that were resistant to both. We also found that 64% of the isolates lacked the genes for production of capsule polysaccharide, which has been proposed to enhance the pathogenic potential of the hospital-associated clonal clusters. In summary, while our collection is not a random sample of cases of E. faecalis endocarditis, these results indicate that nonencapsulated strains belonging to non-hospital-associated lineages were predominant among endocarditis E. faecalis isolates recovered during this time period.

Library screen identifies Enterococcus faecalis CcpA, the catabolite control protein A, as an effector of Ace, a collagen adhesion protein linked to virulence

The Enterococcus faecalis cell wall-anchored protein Ace is an important virulence factor involved in cell adhesion and infection. Expression of Ace on the cell surface is affected by many factors, including stage of growth, culture temperature, and environmental components, such as serum, urine, and collagen. However, the mechanisms that regulate or modulate Ace display are not well understood. With interest in identifying genes associated with Ace expression, we utilized a whole-cell enzyme-linked immunosorbent assay (ELISA)-based screening method to identify mutants from a transposon insertion mutant library which exhibited distinct Ace surface expression profiles. We identified a ccpA insertion mutant which showed significantly decreased levels of Ace surface expression at early growth phase versus those of wild-type OG1RF. Confirmation of the observation was achieved through flow cytometry and complementation analysis. Compared to the wild type, the E. faecalis ccpA mutant had an impaired ability to adhere to collagen when grown to early exponential phase, consistent with the lack of Ace expression in the early growth phase. As a key component of carbon catabolite regulation, CcpA has been previously reported to play a critical role in regulating expression of proteins involved in E. faecalis carbohydrate uptake and utilization. Our discovery is the first to associate CcpA with the production of a major E. faecalis virulence factor, providing new insights into the regulation of E. faecalis pathogenesis.

Expression of the collagen adhesin ace by Enterococcus faecalis strain OG1RF is not repressed by Ers but requires the Ers box

Expression of adhesin to collagen of Enterococcus faecalis (ace), a known virulence factor, is increased by environmental signals such as the presence of serum, high temperature, and bile salts. Currently, the enterococcal regulator of survival (Ers) of E. faecalis strain JH2-2 is the only reported repressor of ace. Here, we show that for strain OG1RF, Ers is not involved in the regulation of ace. Our data showed similar levels of ace expression by OG1RF and its Δers derivative in the presence of bile salts, serum, and high temperature. Using ace promoter-lacZ fusions and site-directed mutagenesis, we confirmed these results and further showed that, while the previously designated Ers box is important for increased expression from the ace promoter of OG1RF, the region responsible for the increase is bigger than the Ers box. In summary, these results indicate that, in strain OG1RF, Ers is not a repressor of ace expression. Although JH2-2 and OG1RF differ by six nucleotides in the region upstream of ace as well as in production of Fsr and gelatinase, the reason(s) for the difference in ace expression between JH2-2 and OG1RF and for increased ace expression in bile, serum and at 46 °C remain(s) to be determined.

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.

Survey of Virulence Determinants among Vancomycin Resistant Enterococcus faecalis and Enterococcus faecium Isolated from Clinical Specimens of Hospitalized Patients of North west of Iran

Recent data indicates an increasing rate of vancomycin resistance in clinical enterococcal isolates worldwide. The nosocomial enterococci are likely to harbor virulence elements that increase their ability to colonize hospitalized patients. The aim of this study was to characterize virulence determinants in vancomycin-resistant enterococci (VRE) obtained from various clinical sources.

During the years 2008 to 2010, a total of 48 VRE isolates were obtained from three University teaching hospitals in Northwest, Iran. Initially, phenotypic speciation was done and minimum inhibitory concentrations (MICs) of vancomycin were determined by agar dilution method and E-test. Then, species identification and resistance genotypes along with detection of virulence genes (asa1, esp, gelE, ace and cpd) of the isolates were performed by multiplex PCR.

Thirty eight isolates were identified as vancomycin-resistant Enterococcus faecium (VREfm) and ten as E. faecalis (VREfs). Irrespective of the species, vanA gene (89.58%) was dominant and three phenotypically vancomycin susceptible E. faecium isolates carried the vanB gene. Among virulence genes investigated, the esp was found in 27(71%) VREfm strains, but did not in any VREfs. Other virulence determinants were highly detected in VREfs strains. Our data indicate a high prevalence of E. faecium harboring vancomycin resistance with vanA genotype and the two VRE species displayed different virulence genes.

Characterization of enterococcus strains contained in probiotic products

Probiotics are additives containing live microbes that beneficially affect a host by improving the properties of the host intestinal microflora. Recently, advances in medical treatments have led to increased numbers of immunocompromised patients; some patients contract opportunistic infections of Enterococcus species, which are considered non-pathogenic bacteria. To evaluate the safety of probiotics containing Enterococcus strains, we isolated Enterococcus from six probiotic products and compared the pathogenic genes and antimicrobial susceptibility of the probiotic strains to those of clinical isolates. Our study showed that all Enterococcus strains contained in probiotic products were E. faecium, and no vancomycin-resistant strains were found. In addition, no pathogenic genes, such as ace, agg, gelE, cylM, cylB, cylA, cpd, cob, ccf, efaA(fs), efaA(fm), esp(fs), or esp(fm), were found in the probiotic strains. Pulsed-field gel electrophoresis (PFGE) analysis showed obvious genetic differences between the probiotic strains and the clinical isolates. The data suggested that the probiotic Enterococcus strains were not transmitted to hospitalized patients. Therefore, our results strongly suggest that probiotic products are unlikely agents for causing opportunistic infections.

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.

Conservation of Ebp-type pilus genes among Enterococci and demonstration of their role in adherence of Enterococcus faecalis to human platelets

Ebp are endocarditis- and biofilm-associated pili of Enterococcus faecalis that are also important in experimental urinary tract infections (UTIs). Our analyses, using available genomes, found that the ebp locus is unique to enterococci. In E. faecalis, the ebp locus is very highly conserved and only 1/473 E. faecalis isolates tested lacked ebpABC, while only 1.2% had the bee pilus locus. No other pilus-encoding operon was identified in 55 available genomes, indicating that the vast majority of E. faecalis strains (unlike Enterococcus faecium and streptococci) have a single pilus locus. Surface expression studies showed that Ebp pili were produced in vitro by 91/91 brain heart infusion (BHI) plus serum-grown E. faecalis isolates and that strain OG1RF expressed pili at even higher levels in rat endocarditis vegetations. However, Ebp expression was restricted to 30 to 72% of E. faecalis cells, consistent with a bistability mode of expression. We also evaluated E. faecalis interactions with human platelets and found that growth of E. faecalis in BHI plus serum significantly enhanced adherence to human platelets and that sortase deletion mutants (the ΔsrtA, Δbps, and ΔbpsΔsrtA mutants) were markedly defective. Further studies identified that Ebp pili, but not the microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) Ace and Fss2, mediate adherence of E. faecalis to platelets. Taken together, our data show that the immunogenic (in human endocarditis patients) and commonly expressed Ebp pili, which are known to be important for experimental endocarditis, are highly conserved and mediate adherence to platelets, suggesting that Ebp pili may be a reasonable immunotherapeutic target for prevention or possibly treatment of endocarditis caused by this species.

Detection and diversity of a putative novel heterogeneous polymorphic proline-glycine repeat (Pgr) protein in the footrot pathogen Dichelobacter nodosus

Dichelobacter nodosus, a Gram-negative anaerobic bacterium, is the essential causative agent of footrot in sheep. Currently, depending on the clinical presentation in the field, footrot is described as benign or virulent; D. nodosus strains have also been classified as benign or virulent, but this designation is not always consistent with clinical disease. The aim of this study was to determine the diversity of the pgr gene, which encodes a putative proline-glycine repeat protein (Pgr). The pgr gene was present in all 100 isolates of D. nodosus that were examined and, based on sequence analysis had two variants, pgrA and pgrB. In pgrA, there were two coding tandem repeat regions, R1 and R2: different strains had variable numbers of repeats within these regions. The R1 and R2 were absent from pgrB. Both variants were present in strains from Australia, Sweden and the UK, however, only pgrB was detected in isolates from Western Australia. The pgrA gene was detected in D. nodosus from tissue samples from two flocks in the UK with virulent footrot and only pgrB from a flock with no virulent or benign footrot for >10 years. Bioinformatic analysis of the putative PgrA protein indicated that it contained a collagen-like cell surface anchor motif. These results suggest that the pgr gene may be a useful molecular marker for epidemiological studies.

Comparative genomic analysis reveals significant enrichment of mobile genetic elements and genes encoding surface structure-proteins in hospital-associated clonal complex 2 Enterococcus faecalis

Background

Enterococci rank among the leading causes of nosocomial infections. The failure to identify pathogen-specific genes in Enterococcus faecalis has led to a hypothesis where the virulence of different strains may be linked to strain-specific genes, and where the combined endeavor of the different gene-sets result in the ability to cause infection. Population structure studies by multilocus sequence typing have defined distinct clonal complexes (CC) of E. faecalis enriched in hospitalized patients (CC2, CC9, CC28 and CC40).

Results

In the present study, we have used a comparative genomic approach to investigate gene content in 63 E. faecalis strains, with a special focus on CC2. Statistical analysis using Fisher's exact test revealed 252 significantly enriched genes among CC2-strains. The majority of these genes were located within the previously defined mobile elements phage03 (n = 51), efaB5 (n = 34) and a vanB associated genomic island (n = 55). Moreover, a CC2-enriched genomic islet (EF3217 to -27), encoding a putative phage related element within the V583 genome, was identified. From the draft genomes of CC2-strains HH22 and TX0104, we also identified a CC2-enriched non-V583 locus associated with the E. faecalis pathogenicity island (PAI). Interestingly, surface related structures (including MSCRAMMs, internalin-like and WxL protein-coding genes) implicated in virulence were significantly overrepresented (9.1%; p = 0.036, Fisher's exact test) among the CC2-enriched genes.

Conclusion

In conclusion, we have identified a set of genes with potential roles in adaptation or persistence in the hospital environment, and that might contribute to the ability of CC2 E. faecalis isolates to cause disease.

Importance of the collagen adhesin ace in pathogenesis and protection against Enterococcus faecalis experimental endocarditis

Ace is an adhesin to collagen from Enterococcus faecalis expressed conditionally after growth in serum or in the presence of collagen. Here, we generated an ace deletion mutant and showed that it was significantly attenuated versus wild-type OG1RF in a mixed infection rat endocarditis model (P<0.0001), while no differences were observed in a peritonitis model. Complemented OG1RFΔace (pAT392::ace) enhanced early (4 h) heart valve colonization versus OG1RFΔace (pAT392) (P = 0.0418), suggesting that Ace expression is important for early attachment. By flow cytometry using specific anti-recombinant Ace (rAce) immunoglobulins (Igs), we showed in vivo expression of Ace by OG1RF cells obtained directly from infected vegetations, consistent with our previous finding of anti-Ace antibodies in E. faecalis endocarditis patient sera. Finally, rats actively immunized against rAce were less susceptible to infection by OG1RF than non-immunized (P = 0.0004) or sham-immunized (P = 0.0475) by CFU counts. Similarly, animals given specific anti-rAce Igs were less likely to develop E. faecalis endocarditis (P = 0.0001) and showed fewer CFU in vegetations (P = 0.0146). In conclusion, we have shown for the first time that Ace is involved in pathogenesis of, and is useful for protection against, E. faecalis experimental endocarditis.

Enterococcus faecalis was recognized as a common cause of infective endocarditis (IE) by the early 1900s. It is still third in community-onset IE, but is the second most common cause of hospital-associated IE. Complications due to E. faecalis IE include congestive heart failure, septic emboli and death and current management involves a combination of antimicrobials, often with surgery. Emergence of antimicrobial resistance has created the need for alternative strategies (such as immunoprophylaxis) that target in vivo expressed virulence-associated surface proteins. One such E. faecalis protein is Ace, which is antigenic during human IE and mediates attachment of E. faecalis cells to host extracellular matrix proteins collagen and laminin. Using a rat model, we now show that ace contributes to E. faecalis IE pathogenesis and demonstrate that Ace is expressed at high levels during IE even though produced at low levels under laboratory conditions; both active and passive immunization based on the collagen-binding domain of Ace conferred significant protection against IE. These observations, along with data that human antibodies against Ace inhibit collagen adherence of E. faecalis, indicate that Ace is an important virulence-associated factor and a promising target for prophylactic and possibly therapeutic strategies against E. faecalis IE.

Review of virulence factors of enterococcus: an emerging nosocomial pathogen

Enterococcus, considered a normal commensal of intestinal tract, is fast emerging as a pathogen causing serious and life threatening hospital borne infections. This is attributed to acquisition of multi drug resistance and virulence factors of the organisms. The sequencing of Enterococcus faecalis has given a lot of insight into its genetic makeup. The E. faecalis strain V583, which has been sequenced, contains a total of 3182 open reading frames (ORFs) with 1760 of these showing similarity to known proteins and 221 of unknown functions. Strikingly unique to this genome is the fact that over 25% of the genome is made up of mobile and exogenously acquired DNA which includes a number of conjugative and composite transposons, a pathogenicity island, integrated plasmid genes and phage regions, and a high number of insertion sequence (IS) elements. This review addresses the genomic arrangement and the study of virulence factors that have occurred since the sequencing of the genome.

LPxTG surface proteins of enterococci

Enterococci have become an important cause of nosocomial infections since the late 1980s. Several surface proteins have been implicated in contributing to infections caused by Enterococcus faecalis and Enterococcus faecium. Understanding the in vivo function of enterococcal surface proteins, particularly their role in directing interactions with the host during infection, is essential to explain the success of enterococci as nosocomial pathogens. Here we review current knowledge of enterococcal LPxTG surface proteins, including aggregation substance, enterococcal surface protein, three collagen-binding microbial surface components that recognize adhesive matrix molecules (Ace, Acm, Scm) and pili (Ebp, PilA and PilB), their interactions with host molecules and their role in pathogenicity and biofilm development.

Virulence of Enterococcus isolates collected in Lower Silesia (Poland)

148 enterococcal strains: E.faecalis (108), E.faecium (35), E.gallinarum (3), E.casseliflavus (1) and E.durans (1) from various clinical specimens were investigated for their ability to adhere to Caco-2 and HEp-2 cell lines, and also for the presence of the esp gene, biofilm formation, production of haemolysins, DNAse and lipase. Several types of enterococcal adhesion to both cell lines were noted. An aggregative adherence was the most frequent among E.faecalis and E.faecium isolates. Other species presented various adhesive types. The occurrence of virulence factors in the whole group of strains was as follows: esp gene in 53.4%, biofilm in 45.3%, haemolysins in 15.5%, DNAse in 12.2% and lipase in 33.1% of enterococcal isolates. It appears that the adherence of the enterococci studied was not significantly associated with the presence of virulence factors.

ace, Which encodes an adhesin in Enterococcus faecalis, is regulated by Ers and is involved in virulence

Enterococcus faecalis is an opportunistic pathogen that causes numerous infectious diseases in humans and is a major agent of nosocomial infections. In this work, we showed that the recently identified transcriptional regulator Ers (PrfA like), known to be involved in the cellular metabolism and the virulence of E. faecalis, acts as a repressor of ace, which encodes a collagen-binding protein. We characterized the promoter region of ace, and transcriptional analysis by reverse transcription-quantitative PCR and mobility shift protein-DNA binding assays revealed that Ers directly regulates the expression of ace. Transcription of ace appeared to be induced by the presence of bile salts, probably via the deregulation of ers. Moreover, with an ace deletion mutant and the complemented strain and by using an insect (Galleria mellonella) virulence model, as well as in vivo-in vitro murine macrophage models, we demonstrated for the first time that Ace can be considered a virulence factor for E. faecalis. Furthermore, animal experiments revealed that Ace is also involved in urinary tract infection by E. faecalis.

Possible role of the adhesin ace and collagen adherence in conveying resistance to disinfectants on Enterococcus faecalis

INTRODUCTION

This study aimed to evaluate whether the presence of the ace gene and Ace-mediated binding to collagen confers on Enterococcus faecalis resistance against common endodontic disinfectants.

METHODS

Isogenic strains of E. faecalis: OG1RF (wild-type) and TX5256 (ace insertion mutant of OG1RF) were grown in brain-heart infusion broth at 46 degrees C overnight. Standardized bacterial suspensions were pretreated for 1 h either with acid-soluble collagen or acidified phosphate-buffered saline (ac-PBS). Bacteria were challenged with chlorhexidine digluconate (CHX), iodine potassium-iodide (IKI), sodium hypochlorite (NaOCl), and calcium hydroxide [Ca(OH)(2)]. Samples were removed at 1, 3, and 6 h, and cultured on Todd-Hewitt agar plates. Colonies were counted, the absolute values were log transformed, and the data were statistically analyzed using Fisher's least significant differences test and t-test.

RESULTS

OG1RF was more resistant than TX5256 to IKI, NaOCl, and Ca(OH)(2) (P < 0.05). Collagen-exposed OG1RF was more resistant than the ac-PBS-pretreated OG1RF against CHX at 3 h and against IKI at 1 h (P < 0.05); no significant difference was found against NaOCl. As expected, the ace mutant strain, TX5256, pretreated with collagen or ac-PBS did not differ significantly in viability when challenged with CHX, IKI, and NaOCl. An unexpected result was found for Ca(OH)(2): collagen-pretreated OG1RF and TX5256 were both more susceptible than ac-PBS-pretreated OG1RF and TX5256, respectively (P < 0.05).

CONCLUSION

The presence of the ace gene confers resistance against IKI, NaOCl, and Ca(OH)(2) on E. faecalis. Exposure to collagen makes the wild-type bacterium more resistant against CHX and IKI; however, exposure to collagen apparently decreases resistance to Ca(OH)(2).

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.

The resistance of collagen-associated, planktonic cells of Enterococcus faecalis to calcium hydroxide

This study examined whether collagen association by an endodontic isolate of Enterococcus faecalis conferred resistance to the bacterium against calcium hydroxide. E. faecalis A197A was grown at 46 degrees C until early stationary phase. Standardized bacterial suspensions were pretreated for 1 hour either with acid-soluble collagen or acidified phosphate-buffered saline (ac-PBS) and cultured to determine the baseline viable bacterial numbers. The bacterial suspensions were challenged with calcium hydroxide solution. Samples were removed at 6, 12, and 24 hours and cultured on tryptone soy agar plates. An adherence assay was performed to confirm that the collagen in the pretreatment medium was bound by the bacteria. Significantly more bacteria were cultivated at 12 hours in the collagen-pretreated group than the ac-PBS-pretreated group (p < 0.01). No bacteria could be cultivated at 24 hours in either group. Collagen association by E. faecalis A197A was found to increase the tolerance of the bacterium to calcium hydroxide.

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

Contribution of the collagen adhesin Acm to pathogenesis of Enterococcus faecium in experimental endocarditis

Enterococcus faecium is a multidrug-resistant opportunist causing difficult-to-treat nosocomial infections, including endocarditis, but there are no reports experimentally demonstrating E. faecium virulence determinants. Our previous studies showed that some clinical E. faecium isolates produce a cell wall-anchored collagen adhesin, Acm, and that an isogenic acm deletion mutant of the endocarditis-derived strain TX0082 lost collagen adherence. In this study, we show with a rat endocarditis model that TX0082 Deltaacm::cat is highly attenuated versus wild-type TX0082, both in established (72 h) vegetations (P < 0.0001) and for valve colonization 1 and 3 hours after infection (P or=50-fold reduction relative to an Acm producer) were found in three of these five nonadherent isolates, including the sequenced strain TX0016, by quantitative reverse transcription-PCR, indicating that acm transcription is downregulated in vitro in these isolates. However, examination of TX0016 cells obtained directly from infected rat vegetations by flow cytometry showed that Acm was present on 40% of cells grown during infection. Finally, we demonstrated a significant reduction in E. faecium collagen adherence by affinity-purified anti-Acm antibodies from E. faecium endocarditis patient sera, suggesting that Acm may be a potential immunotarget for strategies to control this emerging pathogen.

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.

Large scale variation in Enterococcus faecalis illustrated by the genome analysis of strain OG1RF

A comparison of two strains of the hospital pathogen Enterococcus faecalis suggests that mediators of virulence differ between strains and that virulence does not depend on mobile gene elements

Background

Enterococcus faecalis has emerged as a major hospital pathogen. To explore its diversity, we sequenced E. faecalis strain OG1RF, which is commonly used for molecular manipulation and virulence studies.

Results

The 2,739,625 base pair chromosome of OG1RF was found to contain approximately 232 kilobases unique to this strain compared to V583, the only publicly available sequenced strain. Almost no mobile genetic elements were found in OG1RF. The 64 areas of divergence were classified into three categories. First, OG1RF carries 39 unique regions, including 2 CRISPR loci and a new WxL locus. Second, we found nine replacements where a sequence specific to V583 was substituted by a sequence specific to OG1RF. For example, the iol operon of OG1RF replaces a possible prophage and the vanB transposon in V583. Finally, we found 16 regions that were present in V583 but missing from OG1RF, including the proposed pathogenicity island, several probable prophages, and the cpsCDEFGHIJK capsular polysaccharide operon. OG1RF was more rapidly but less frequently lethal than V583 in the mouse peritonitis model and considerably outcompeted V583 in a murine model of urinary tract infections.

Conclusion

E. faecalis OG1RF carries a number of unique loci compared to V583, but the almost complete lack of mobile genetic elements demonstrates that this is not a defining feature of the species. Additionally, OG1RF's effects in experimental models suggest that mediators of virulence may be diverse between different E. faecalis strains and that virulence is not dependent on the presence of mobile genetic elements.