Identification of ABC transporters in vancomycin-resistant Enterococcus faecium as potential targets for antibody therapy

Advances and Prospects in Vaccine Development against Enterococci

Enterococci are the second most common Gram-positive pathogen responsible for nosocomial infections. Due to the limited number of new antibiotics that reach the medical practice and the resistance of enterococci to the current antibiotic options, passive and active immunotherapies have emerged as a potential prevention and/or treatment strategy against this opportunistic pathogen. In this review, we explore the pathogenicity of these bacteria and their interaction with the host immune response. We provide an overview of the capsular polysaccharides and surface-associated proteins that have been described as potential antigens in anti-enterococcal vaccine formulations. In addition, we describe the current status in vaccine development against enterococci and address the importance and the current advances toward the development of well-defined vaccines with broad coverage against enterococci.

DNA-based microarray studies in visceral leishmaniasis: identification of biomarkers for diagnostic, prognostic and drug target for treatment

Visceral leishmaniasis (VL) is one of the major infectious diseases affecting the poorest regions of the world. Current therapy is not very much satisfactory. The alarming rise of drug resistance and the unavailability of an effective vaccine against VL urges research towards identifying new targets or biomarkers for its effective treatment. New technology developments offer some fresh hope in its diagnosis, treatment, and control. DNA microarray approach is now broadly used in parasitology research to facilitate the thoughtful of mechanisms of disease and identification of drug targets and biomarkers for diagnostic and therapeutic development. An electronic search on "VL" and "Microarray" was conducted in Medline and Scopus and papers published in the English mentioning use of DNA microarray on VL were selected and read to write this paper review. Functional analysis and interpretation of microarray results remain very challenging due to the inherent nature of experimental workflows, access, cost, and complexity of data obtained. We have explained and emphasized the use of curate knowledge of microarray in the case of VL for the identification of therapeutic target and biomarker and their selection/implementation in clinical use.

Outbreaks caused by vancomycin-resistant Enterococcus faecium in hematology and oncology departments: A systematic review

Background

Vancomycin-resistance in Enterococcus faecium (VRE) poses a major threat in health care settings. It is well known that patients in hematology and oncology departments are especially at risk of nosocomial VRE acquisition. This systematic review of the literature provides data on the main sources, transmission modes and potential risk factors for VRE acquisition as well as appropriate infection control measures in order to terminate such nosocomial outbreaks.

Methods

Data on nosocomial VRE outbreaks on hematology and oncology wards was retrieved from the Outbreak Database and PubMed.

Results

A total of 35 VRE outbreaks describing 757 affected patients and 77 deaths were included in this review. The most frequent site of pathogen detection were stool samples or rectal swabs (57% of all isolation sites), followed by blood cultures (30%). The most common outbreak source was an index patient. The main modes of transmission were 1) hands of health care workers, 2) contact to a contaminated environment and 3) patient-to-patient contact. The most common risk factor for VRE positivity was prior antibiotic treatment. The most common infection control measures performed were screening and isolating or cohorting of patients.

Conclusion

A rational use of antibiotics in hematology and oncology units is recommended in order to reduce selection pressure on resistant pathogens such as VRE. In addition the importance of hand hygiene should be stressed to all staff whenever possible.

Where is the difference between an epidemic and a high endemic level with respect to nosocomial infection control measures? An analysis based on the example of vancomycin-resistant Enterococcus faecium in hematology and oncology departments

Some infection control recommendations distinguish epidemic and endemic levels for infection control. However, it is often difficult to separate long lasting outbreaks from high endemic levels and it remains open, if this distinction is really useful. Aim: To compare infection control measures in endemic and epidemic outbreaks. Methods: The example of vancomycin-resistant Enterococcus faecium outbreaks in haematology or oncology departments was used to analyse differences in infection control measures between outbreaks and high endemic levels. The outbreak database and PubMed, including long lasting outbreaks, were used for this analysis. Two time limits were used for separation: 6 and 12 months. In addition, monoclonal and polyclonal outbreaks were distinguished. Findings: A total of 36 outbreaks were included. 13 outbreaks lasted 6 months or less, 9 outbreaks more than 6 months but at maximum 12 months and 9 more than 12 months. For the remaining outbreaks, no information about their duration was available. Altogether, 11 outbreaks were monoclonal and 20 polyclonal. Considering infection control measures, there were almost no differences between the different groups compared. Patient screening was given up in 37.5% of long lasting outbreaks (>12 months) and hand hygiene not reported in the majority of polyclonal outbreaks (77.8%). Conclusion: Despite many institutions trying to add further infection control measures in case of an outbreak, evidence based infection control measures should be implemented in endemic and epidemic situations. The crucial aspect is probably the degree of implementation and its control in both situations.

Characterization of Two Metal Binding Lipoproteins as Vaccine Candidates for Enterococcal Infections

Background

Enterococcus faecium and faecalis are Gram-positive opportunistic pathogens that have become leading causes of nosocomial infections over the last decades. Especially multidrug resistant enterococci have become a challenging clinical problem worldwide. Therefore, new treatment options are needed and the identification of alternative targets for vaccine development has emerged as a feasible alternative to fight the infections caused by these pathogens.

Results

We extrapolate the transcriptomic data from a mice peritonitis infection model in E. faecalis to identify putative up-regulated surface proteins under infection conditions in E. faecium. After the bionformatic analyses two metal binding lipoproteins were identified to have a high homology (>72%) between the two species, the manganese ABC transporter substrate-binding lipoprotein (PsaA_fm,) and the zinc ABC transporter substrate-binding lipoprotein (AdcA_fm). These candidate lipoproteins were overexpressed in Escherichia coli and purified. The recombinant proteins were used to produce rabbit polyclonal antibodies that were able to induce specific opsonic antibodies that mediated killing of the homologous strain E. faecium E155 as well as clinical strains E. faecium E1162, Enterococcus faecalis 12030, type 2 and type 5. Mice were passively immunized with the antibodies raised against recombinant lipoproteins, showing significant reduction of colony counts in mice livers after the bacterial challenge and demonstrating the efficacy of these metal binding lipoproteins as promising vaccine candidates to treat infections caused by these enterococcal pathogens.

Conclusion

Overall, our results demonstrate that these two metal binding lipoproteins elicited specific, opsonic and protective antibodies, with an extensive cross-reactivity and serotype-independent coverage among these two important nocosomial pathogens. Pointing these two protein antigens as promising immunogens, that can be used as single components or as carrier proteins together with polysaccharide antigens in vaccine development against enterococcal infections.

Identification of peptidoglycan-associated proteins as vaccine candidates for enterococcal infections

Infections by opportunistic bacteria have significant contributions to morbidity and mortality of hospitalized patients and also lead to high expenses in healthcare. In this setting, one of the major clinical problems is caused by Gram-positive bacteria such as enterococci and staphylococci. In this study we extract, purify, identify and characterize immunogenic surface-exposed proteins present in the vancomycin resistant enterococci (VRE) strain Enterococcus faecium E155 using three different extraction methods: trypsin shaving, biotinylation and elution at high pH. Proteomic profiling was carried out by gel-free and gel-nanoLC-MS/MS analyses. The total proteins found with each method were 390 by the trypsin shaving, 329 by the elution at high pH, and 45 using biotinylation. An exclusively extracytoplasmic localization was predicted in 39 (10%) by trypsin shaving, in 47 (15%) by elution at high pH, and 27 (63%) by biotinylation. Comparison between the three extraction methods by Venn diagram and subcellular localization predictors (CELLO v.2.5 and Gpos-mPLoc) allowed us to identify six proteins that are most likely surface-exposed: the SCP-like extracellular protein, a low affinity penicillin-binding protein 5 (PBP5), a basic membrane lipoprotein, a peptidoglycan-binding protein LysM (LysM), a D-alanyl-D-alanine carboxypeptidase (DdcP) and the peptidyl-prolyl cis-trans isomerase (PpiC). Due to their close relationship with the peptidoglycan, we chose PBP5, LysM, DdcP and PpiC to test their potential as vaccine candidates. These putative surface-exposed proteins were overexpressed in Escherichia coli and purified. Rabbit polyclonal antibodies raised against the purified proteins were able to induce specific opsonic antibodies that mediated killing of the homologous strain E. faecium E155 as well as clinical strains E. faecium E1162, Enterococcus faecalis 12030, type 2 and type 5. Passive immunization with rabbit antibodies raised against these proteins reduced significantly the colony counts of E. faecium E155 in mice, indicating the effectiveness of these surface-related proteins as promising vaccine candidates to target different enterococcal pathogens.

Unraveling the protein targets of vancomycin in living S. aureus and E. faecalis cells

Vancomycin is a potent glycopeptide antibiotic that has evolved to specifically bind to the D-Ala-D-Ala dipeptide termini of nascent peptidoglycans. Although this mode of action is well established, several studies indicate that vancomycin and analogues exploit noncanonical target sites. In order to address all vancomycin targets in clinically relevant Staphylococcus aureus and Enterococcus faecalis strains we developed a series of small-molecule photoaffinity probes based on vancomycin. Proteomic profiling revealed the specific labeling of two previously unknown vancomycin targets that are likely to contribute to its antibiotic activity. The specific inhibition of the major staphylococcal autolysin Atl confirms previous observations that vancomycin alters S. aureus cell morphology by interaction with the autolytic machinery. Moreover, in E. faecalis the vancomycin photoprobe specifically binds to an ABC transporter protein, which likely impedes the uptake of essential nutrients such as sugars and peptides. The labeling of these two prominent membrane targets in living cells reveals a thus far unexplored mode of vancomycin binding and inhibition that could allow a rational design of variants with improved activity.

Characterization and evaluation of the Moraxella catarrhalis oligopeptide permease A as a mucosal vaccine antigen

Moraxella catarrhalis is a common cause of otitis media in children and of lower respiratory tract infections in adults with chronic obstructive pulmonary disease; therefore, these two groups would benefit from a vaccine to prevent M. catarrhalis infections. A genome mining approach for vaccine antigens identified oligopeptide permease protein A (OppA), an oligopeptide binding protein of an apparent oligopeptide transport system. Analysis of the oppA gene by PCR and sequence analysis revealed that OppA is highly conserved among clinical isolates of M. catarrhalis. Recombinant OppA was expressed as a lipoprotein and purified, and an oppA knockout mutant was constructed. Antiserum raised to recombinant purified OppA recognized epitopes on the bacterial surface of the wild type but not the OppA knockout mutant. Antibodies raised to purified recombinant OppA recognized native OppA in multiple strains. Intranasal immunization of mice induced systemic and mucosal antibodies to OppA and resulted in enhanced clearance of M. catarrhalis in a mouse pulmonary clearance model. OppA is a highly conserved, immunogenic protein that expresses epitopes on the bacterial surface and that induces potentially protective immune responses in a mouse model. OppA should be evaluated further as a vaccine antigen for M. catarrhalis.

Enterococcal surface protein contributes to persistence in the host but is not a target of opsonic and protective antibodies in Enterococcus faecium infection

Enterococci are important nosocomial pathogens with multiple intrinsic and acquired resistances to antibiotics. In the past, the majority of infections were caused by Enterococcus faecalis; however, an increase in Enterococcus faecium clinical isolates has been observed in recent years. The enterococcal surface protein (Esp) is expressed on the surface of most E. faecium clinical isolates and has been shown to be involved in biofilm formation. Here, E. faecium E1162 and its previously created insertion-deletion mutant of the esp gene, E. faecium E1162Δesp, were compared in a mouse bacteraemia model. Anti-Esp serum was tested for its capacity to mediate opsonophagocytic killing of E1162 in vitro and to protect against E. faecium bacteraemia. The inactivation of esp attenuated E. faecium virulence with reduced numbers of bacteria recovered from the kidneys in animals infected with the mutant compared to the wild-type strain (P=0.035). Passive immunization with rabbit polyclonal serum raised against the recombinant N-terminal Esp protein did not protect mice against E. faecium bacteraemia (P>0.05). In contrast, mice passively immunized with polyclonal antiserum raised against lipoteichoic acid (LTA) from E. faecalis had lower numbers of E. faecium E1162 in the blood compared to mice immunized with normal rabbit serum. These results suggest that Esp contributes to E. faecium persistence in the host. However, in contrast to LTA, Esp does not seem to be a target for protective antibodies in E. faecium strain E1162 in mouse bacteraemia.

Monoclonal antibodies for prophylaxis and therapy of infectious diseases

Monoclonal antibodies (mAb) are attractive biologic drugs due to their exquisite specificity and well understood mechanisms of action, which results in a higher predictability and lower attrition rate compared with other drugs. Therefore, it may seem surprising that only a single mAb is presently marketed for an infectious disease indication. However, the antibiotic resistance crisis, emerging viral diseases and bioterroristic threats have recently spurred the development of anti-infective mAbs, of which more than a dozen are being tested in clinical trials. Conceptually, and validated in many preclinical models, mAbs will be most effective when used prophylactically against acute viral infections and bacterial toxins. The acute bacterial and chronic viral infections, which are medically and economically far more important, are much more difficult to control by antibodies, as the recent clinical failure of some polyclonal antibody products has shown. In these situations, the synergistic action of two or more mAbs together with a small molecule drug will most likely be required for therapeutic efficacy. This review aims to highlight the scientific and economic opportunities and obstacles that are encountered in the quest to add mAbs to the armament of anti-infective drugs.

Protection against heartwater by DNA immunisation with four Ehrlichia ruminantium open reading frames

We have reported previously that a recombinant DNA vaccine consisting of four Ehrlichia ruminantium (Welgevonden) open reading frames (ORFs) known as the 1H12 cocktail provided protection against a virulent E. ruminantium (Welgevonden) needle challenge in sheep. In this study, we have investigated the vaccine effectiveness of two other cocktails of E. ruminantium (Welgevonden) ORFs, as well as single ORFs from the 1H12 cocktail, to protect sheep against a virulent needle challenge with the homologous strain. Each individual 1H12 ORF provided protection, but all the animals vaccinated with the other cocktails succumbed to the challenge.

Treatment and prevention of enterococcal infections--alternative and experimental approaches

Enterococci are one of the leading types of organisms isolated from infections of hospitalised patients and the third most common cause of nosocomial bloodstream infections. They contribute significantly to patient mortality and morbidity, as well as healthcare costs. The emergence of resistance against virtually all clinically available antibiotics and the ability to transfer these resistance determinants to other pathogens demonstrates the urgency for an improved understanding of enterococcal virulence mechanisms, and the development of alternative treatment and prevention options. This article reviews new antimicrobials, vaccine targets, bacteriophage therapy, as well as treatments targeting virulence factors and biofilm, for their potential to treat and/or prevent enterococcal infections. Although clinical isolates often cause serious infections, so-called 'non-pathogenic' strains are used as therapeutics in the form of probiotics. Understanding the differences between true pathogens and beneficial commensals may help to evaluate future treatment and prophylactic options.

Rationale for the development of immunotherapy regimens against enterococcal infections

Enterococci are the third most common pathogen isolated in bloodstream infections. Increasing resistance against multiple antimicrobial agents has left few treatment options for enterococcal infections, and alternative therapeutic approaches are needed. Although a variety of virulence factors have been described for Enterococcus faecalis, only aggregation substance (AS) and a teichoic acid-like capsular polysaccharide have been evaluated for their potential for vaccine development. Antibodies raised against purified capsular polysaccharide are highly opsonic and protect mice against bacteremia after active and passive immunization. Since E. faecalis expresses only a limited number of capsular serotypes, this antigen may be an attractive candidate for development of a conjugate vaccine.

Speciation in Chlamydia: genomewide phylogenetic analyses identified a reliable set of acquired genes

Horizontal gene transfer (HGT), a process through which genomes acquire sequences from distantly related organisms, is believed to be a major source of genetic diversity in bacteria. A central question concerning the impact of HGT on bacterial genome evolution is the proportion of horizontally transferred sequences within genomes. This issue, however, remains unresolved because the various methods developed to detect potential HGT events identify different sets of genes. The present-day consensus is that phylogenetic analysis of individual genes is still the most objective and accurate approach for determining the occurrence and directionality of HGT. Here we present a genome-scale phylogenetic analysis of protein-encoding genes from five closely related Chlamydia, identifying a reliable set of sequences that have arisen via HGT since the divergence of the Chlamydia lineage. According to our knowledge, this is the first systematic phylogenetic inference-based attempt to establish a reliable set of acquired genes in a bacterial genome. Although Chlamydia are obligate intracellular parasites of higher eukaryotes, and thus suspected to be isolated from HGT more than the free-living species, our results show that their diversification has involved the introduction of foreign sequences into their genome. Furthermore, we also identified a complete set of genes that have undergone deletion, duplication, or rearrangement during this evolutionary period leading to the radiation of Chlamydia species. Our analysis may provide a deeper insight into how these medically important pathogens emerged and evolved from a common ancestor.

Enterococcal infections: host response, therapeutic, and prophylactic possibilities

The emergence of resistance against multiple antibiotics and the increasing frequency with which Enterococcus faecalis and Enterococcus faecium are isolated from hospitalized patients underscore the necessity for a better understanding of the virulence mechanisms of this pathogen and the development of alternatives to current antibiotic treatments. The genetic plasticity of enterococci and their ability to rapidly acquire and/or develop resistance against many clinically important antibiotics and to transfer these resistance determinants to other more pathogenic microorganisms makes the search for alternative treatment and preventive options even more important. A capsular polysaccharide antigen has recently been characterized that is the target of opsonic antibodies. A limited number of clinically relevant serotypes exist, and the development of an enterococcal vaccine based on capsular polysaccharides may improve our ability to prevent and treat these infections. Additional enterococcal surface antigens, including ABC transporter proteins and other virulence factors, such as aggregation substance (AS), may also be useful targets for therapeutic antibodies.

Direct isolation of recombinant human antibodies against group B Neisseria meningitidis from scFv expression libraries

The successful generation of human antibodies from large nai;ve antibody libraries requires iterative selection steps. Here, we describe a new and fast method for the isolation of high affinity antibodies directly from human single chain Fv antibody (scFv) expression libraries. Escherichia coli scFv expression libraries were made from peripheral blood lymphocytes from four individuals vaccinated with group B Neisseria meningitidis outer membrane vesicle (OMV) vaccine. Forty thousand clones were directly screened for antibodies binding N. meningitidis strain 44/76 (B:15:P1.7,16). Of 430 specific clones detected, 225 candidates were isolated and re-screened against the N. meningitidis strains NZ-98/254 (B:4:P1.7b,4) giving 4% cross-reactive clones. Antibodies were further characterized by DNA sequencing, ELISA and surface plasmon resonance (SPR) analysis, showing broad V-gene diversity and nanomolar scFv affinities. Antibodies derived by this method may assist in the discovery and development of new vaccine antigens as well as therapeutic antibody agents for the treatment of meningococcal diseases.