Identification of an immunodominant ABC transporter in methicillin-resistant Staphylococcus aureus infections

Transcriptomic analysis of Staphylococcus equorum KM1031 from the high-salt fermented seafood jeotgal under chloramphenicol, erythromycin and lincomycin stresses

Staphylococcus equorum strain KM1031 is resistant to chloramphenicol, erythromycin and lincomycin. To shed light on the genetic factors underlying these antibiotic resistances, we determined the global gene expression profile of S. equorum KM1031 using RNA sequencing. During chloramphenicol, erythromycin and lincomycin treatment, 8.3% (183/2,336), 16.0% (354/2,336), and 2.9% (63/2,336) of S. equorum KM1031 genes exhibited significant differences in expression, respectively. These three antibiotics upregulated genes related to efflux and downregulated genes related to transporters. Antibiotic treatment also upregulated osmoprotectant-related genes involved in salt tolerance. To identify specific genes functionally related to antibiotic resistance, we compared the genome of strain KM1031 with those of three S. equorum strains that are sensitive to these three antibiotics. We identified three genes of particular interest: an antibiotic biosynthesis monooxygenase gene (abm, AWC34_RS01805) related to chloramphenicol resistance, an antibiotic ABC transporter ATP-binding protein gene (msr, AWC34_RS11115) related to erythromycin resistance, and a lincosamide nucleotydyltransferase gene (lnuA, AWC34_RS13300) related to lincomycin resistance. These genes were upregulated in response to the corresponding antibiotic; in particular, msr was upregulated more than fourfold by erythromycin treatment. Finally, the results of RNA sequencing were validated by quantitative real-time PCR. This transcriptomic analysis provides genetic evidence regarding antibiotic stress responses of S. equorum strain KM1031.

Biofilm matrix proteome of clinical strain of P. aeruginosa isolated from bronchoalveolar lavage of patient in intensive care unit

Extracellular matrix plays a pivotal role in biofilm biology and proposed as a potential target for therapeutics development. As matrix is responsible for some extracellular functions and influence bacterial cytotoxicity against eukaryotic cells, it must have unique protein composition. P. aeruginosa is one of the most important pathogens with emerging antibiotic resistance, but only a few studies were devoted to matrix proteomes and there are no studies describing matrix proteome for any clinical isolates except reference strains PAO1 and ATCC27853. Here we report the first biofilm matrix proteome of P. aeruginosa isolated from bronchoalveolar lavage of patient in intensive care unit. We have identified the largest number of proteins in the matrix among all published studies devoted to P. aeruginosa biofilms. Comparison of matrix proteome with proteome from embedded cells let us to identify several enriched bioprocess groups. Bioprocess groups with the largest number of overrepresented in matrix proteins were oxidation-reduction processes, proteolysis, and transmembrane transport. The top three represented in matrix bioprocesses concerning the size of the GO annotated database were cell redox homeostasis, nucleoside metabolism, and fatty acid synthesis. Finally, we discuss the obtained data in a prism of antibiofilm therapeutics development.

Molecular Targets for Antibody-Based Anti-Biofilm Therapy in Infective Endocarditis

Infective endocarditis (IE) is a heart disease caused by the infection of heart valves, majorly caused by Staphilococcus aureus. IE is initiated by bacteria entering the blood circulation in favouring conditions (e.g., during invasive procedures). So far, the conventional antimicrobial strategies based on the usage of antibiotics remain the major intervention for treating IE. Nevertheless, the therapeutic efficacy of antibiotics in IE is limited not only by the bacterial drug resistance, but also by the formation of biofilms, which resist the penetration of antibiotics into bacterial cells. To overcome these drawbacks, the development of anti-biofilm treatments that can expose bacteria and make them more susceptible to the action of antibiotics, therefore resulting in reduced antimicrobial resistance, is urgently required. A series of anti-biofilm strategies have been developed, and this review will focus in particular on the development of anti-biofilm antibodies. Based on the results previously reported in the literature, several potential anti-biofilm targets are discussed, such as bacterial adhesins, biofilm matrix and bacterial toxins, covering their antigenic properties (with the identification of potential promising epitopes), functional mechanisms, as well as the antibodies already developed against these targets and, where feasible, their clinical translation.

Identification of a rabbit Ig light chain recombinant protein bound to serum immunoglobulins from different marine fish species

The structures of fish serum immunoglobulin differ among different fish species. In this study, we accidently isolated a rabbit immunoglobulin (Ig) light chain bound to serum immunoglobulin from different marine fish species using phage display. Fish Ig was separated using a protein A column. The phage library was generated from variable regions of rabbit spleen B cells immunized with bluefin tuna Thunnus orientalis Ig. Fish Ig-specific phages were enriched using two rounds of bio-panning with yellowtail Seriola quinqueradiata serum Ig, followed by two rounds of bio-panning with red seabream Pagrus major serum Ig. The enriched phages demonstrated an increase in binding specificity to the tuna, yellowtail, and red seabream Igs compared to the phages listed in the unpanned library. A recombinant protein of a single clonal phage, which encodes the rabbit Ig light chain, was produced, and the binding specificities to fish Igs were analyzed using enzyme-linked immunosorbent assay (ELISA) and western blotting. The recombinant protein exhibited binding properties to fish Igs in the ELISA. However, the recombinant protein that bound to serum protein(s), but not IgM, was detected via western blotting. The recombinant protein may provide a novel information on the common structural feature in the fish immunoglobulins.

Bactericidal fully human single-chain fragment variable antibodies protect mice against methicillin-resistant Staphylococcus aureus bacteraemia

OBJECTIVES

The increasing prevalence of antibiotic-resistant Staphylococcus aureus, besides the inadequate numbers of effective antibiotics, emphasises the need to find new therapeutic agents against this lethal pathogen.

METHODS

In this study, to obtain antibody fragments against S. aureus, a human single-chain fragment variable (scFv) library was enriched against living methicillin-resistant S. aureus (MRSA) cells, grown in three different conditions, that is human peripheral blood mononuclear cells with plasma, whole blood and biofilm. The antibacterial activity of scFvs was evaluated by the growth inhibition assay in vitro. Furthermore, the therapeutic efficacy of anti-S. aureus scFvs was appraised in a mouse model of bacteraemia.

RESULTS

Three scFv antibodies, that is MEH63, MEH158 and MEH183, with unique sequences, were found, which exhibited significant binding to S. aureus and reduced the viability of S. aureus in in vitro inhibition assays. Based on the results, MEH63, MEH158 and MEH183, in addition to their combination, could prolong the survival rate, reduce the bacterial burden in the blood and prevent inflammation and tissue destruction in the kidneys and spleen of mice with MRSA bacteraemia compared with the vehicle group (treated with normal saline).

CONCLUSION

The combination therapy with anti-S. aureus scFvs and conventional antibiotics might shed light on the treatment of patients with S. aureus infections.

Monoclonal Antibodies Targeting Surface-Exposed and Secreted Proteins from Staphylococci

Staphylococci (specifically Staphylococcus aureus and Staphylococcus epidermidis) are the causative agents of diseases ranging from superficial skin and soft tissue infections to severe conditions such as fatal pneumonia, bacteremia, sepsis and endocarditis. The widespread and indiscriminate use of antibiotics has led to serious problems of resistance to staphylococcal disease and has generated a renewed interest in alternative therapeutic agents such as vaccines and antibodies. Staphylococci express a large repertoire of surface and secreted virulence factors, which provide mechanisms (adhesion, invasion and biofilm development among others) for both bacterial survival in the host and evasion from innate and adaptive immunity. Consequently, the development of antibodies that target specific antigens would provide an effective protective strategy against staphylococcal infections. In this review, we report an update on efforts to develop anti-staphylococci monoclonal antibodies (and their derivatives: minibodies, antibody–antibiotic conjugates) and the mechanism by which such antibodies can help fight infections. We also provide an overview of mAbs used in clinical trials and highlight their therapeutic potential in various infectious contexts.

An Immunodominant Epitope-Specific Monoclonal Antibody Cocktail Improves Survival in a Mouse Model of Staphylococcus aureus Bacteremia

To date, no vaccine or monoclonal antibody (mAb) against Staphylococcus aureus has been approved for use in humans. Our laboratory has developed a 5-antigen S. aureus vaccine (rFSAV), which is now under efficacy evaluation in a phase 2 clinical trial. In the current study, using overlapping peptides and antiserum from rFSAV-immunized volunteers, we identified 7 B-cell immunodominant epitopes on 4 antigens in rFSAV, including 5 novel epitopes (Hla48-65, IsdB402-419, IsdB432-449, SEB78-95, and MntC7-24). Ten immunodominant epitope mAbs were generated against these epitopes, and all of them exhibited partial protection in a mouse sepsis model. Four robust mAbs were used together as an mAb cocktail to prevent methicillin-resistant S. aureus strain 252 infection. The results showed that the mAb cocktail was efficient in combating S. aureus infection and that its protective efficacy correlated with a reduced bacterial burden and decreased infection pathology, which demonstrates that the mAb cocktail is a promising S. aureus vaccine candidate.

Fighting Staphylococcus aureus Biofilms with Monoclonal Antibodies

Staphylococcus aureus (S. aureus) is a notorious pathogen and one of the most frequent causes of biofilm-related infections. The treatment of S. aureus biofilms is hampered by the ability of the biofilm structure to shield bacteria from antibiotics as well as the host's immune system. Therefore, new preventive and/or therapeutic interventions, including the use of antibody-based approaches, are urgently required. In this review, we describe the mechanisms by which anti-S. aureus antibodies can help in combating biofilms, including an up-to-date overview of monoclonal antibodies currently in clinical trials. Moreover, we highlight ongoing efforts in passive vaccination against S. aureus biofilm infections, with special emphasis on promising targets, and finally indicate the direction into which future research could be heading.

Antibody-Based Agents in the Management of Antibiotic-Resistant Staphylococcus aureus Diseases

Staphylococcus aureus is a human pathogen that can cause a wide spectrum of diseases, including sepsis, pneumonia, arthritis, and endocarditis. Ineffective treatment of a number of staphylococcal infections with antibiotics is due to the development and spread of antibiotic-resistant strains following decades of antibiotic usage. This has generated renewed interest within the scientific community in alternative therapeutic agents, such as anti-S. aureus antibodies. Although the role of antibodies in the management of S. aureus diseases is controversial, the success of this pathogen in neutralizing humoral immunity clearly indicates that antibodies offer the host extensive protection. In this review, we report an update on efforts to develop antibody-based agents, particularly monoclonal antibodies, and their therapeutic potential in the passive immunization approach to the treatment and prevention of S. aureus infections.

Vaccines and Immunotherapy for Staphylococcal Infections

Nosocomial or hospital-acquired infections are associated with prolonged hospitalizations and increased healthcare costs. Infections associated with surgical implants are becoming more difficult and more costly to manage, as they require repeated surgical procedures and a longer period of time to treat patients. Continued advances in the use of medical devices, an increase in the number of immunocompromised patients, and a steady rise in the prevalence of antibiotic-resistant organisms has renewed interest in the development of novel therapies that can be used to prevent and treat nosocomial infections. This review provides an overview of bacterial adhesins and focuses on novel immunological therapies developed to treat staphylococcal infections.

Monoclonal Antibodies and Antibody Like Fragments Derived from Immunised Phage Display Libraries

Morbidity and mortality associated with infectious diseases are always on the rise, especially in poorer countries and in the aging population. The inevitable, but unpredictable emergence of new infectious diseases has become a global threat. HIV/AIDS, severe acute respiratory syndrome (SARS), and the more recent H1N1 influenza are only a few of the numerous examples of emerging infectious diseases in the modern era. However despite advances in diagnostics, therapeutics and vaccines, there is need for more specific, efficacious, cost-effective and less toxic treatment and preventive drugs. In this chapter, we discuss a powerful combinatorial technology in association with animal immunisation that is capable of generating biologic drugs with high affinity, efficacy and limited off-site toxicity, and diagnostic tools with great precision. Although time consuming, immunisation still remains the preferred route for the isolation of high-affinity antibodies and antibody-like fragments. Phage display is a molecular diversity technology that allows the presentation of large peptide and protein libraries on the surface of filamentous phage. The selection of binding fragments from phage display libraries has proven significant for routine isolation of invaluable peptides, antibodies, and antibody-like domains for diagnostic and therapeutic applications. Here we highlight the many benefits of combining immunisation with phage display in combating infectious diseases, and how our knowledge of antibody engineering has played a crucial role in fully exploiting these platforms in generating therapeutic and diagnostic biologics towards antigenic targets of infectious organisms.

From Erythromycin to Azithromycin and New Potential Ribosome-Binding Antimicrobials

Macrolides, as a class of natural or semisynthetic products, express their antibacterial activity primarily by reversible binding to the bacterial 50S ribosomal subunits and by blocking nascent proteins’ progression through their exit tunnel in bacterial protein biosynthesis. Generally considered to be bacteriostatic, they may also be bactericidal at higher doses. The discovery of azithromycin from the class of macrolides, as one of the most important new drugs of the 20th century, is presented as an example of a rational medicinal chemistry approach to drug design, applying classical structure-activity relationship that will illustrate an impressive drug discovery success story. However, the microorganisms have developed several mechanisms to acquire resistance to antibiotics, including macrolide antibiotics. The primary mechanism for acquiring bacterial resistance to macrolides is a mutation of one or more nucleotides from the binding site. Although azithromycin is reported to show different, two-step process of the inhibition of ribosome function of some species, more detailed elaboration of that specific mode of action is needed. New macrocyclic derivatives, which could be more potent and less prone to escape bacterial resistance mechanisms, are also continuously evaluated. A novel class of antibiotic compounds—macrolones, which are derived from macrolides and comprise macrocyclic moiety, linker, and either free or esterified quinolone 3-carboxylic group, show excellent antibacterial potency towards key erythromycin-resistant Gram-positive and Gram-negative bacterial strains, with possibly decreased potential of bacterial resistance to macrolides.

Proteome-wide antigen discovery of novel protective vaccine candidates against Staphylococcus aureus infection

Methicillin-resistant Staphylococcus aureus (MRSA) is a rapidly growing problem, especially in hospitals where MRSA cause increased morbidity and mortality and a significant rise in health expenditures. As many strains of MRSA are resistant to other antimicrobials in addition to methicillin, there is an urgent need to institute non-antimicrobial measures, such as vaccination, against the spread of MRSA. With the aim of finding new protective antigens for vaccine development, this study used a proteome-wide in silico antigen prediction platform to screen the proteome of S. aureus strain MRSA252. Thirty-five different S. aureus proteins were identified, recombinantly expressed, and tested for protection in a lethal sepsis mouse model using S. aureus strain MRSA252 as the challenge organism. We found that 13 of the 35 recombinant peptides yielded significant protection and that 12 of these antigens were highly conserved across 70 completely sequenced S. aureus strains. Thus, this in silico platform was capable of identifying novel candidates for inclusion in future vaccines against MRSA.

Orthopaedic device-related infection: current and future interventions for improved prevention and treatment

Orthopaedic and trauma device-related infection (ODRI) remains one of the major complications in modern trauma and orthopaedic surgery.Despite best practice in medical and surgical management, neither prophylaxis nor treatment of ODRI is effective in all cases, leading to infections that negatively impact clinical outcome and significantly increase healthcare expenditure.The following review summarises the microbiological profile of modern ODRI, the impact antibiotic resistance has on treatment outcomes, and some of the principles and weaknesses of the current systemic and local antibiotic delivery strategies.The emerging novel strategies aimed at preventing or treating ODRI will be reviewed. Particular attention will be paid to the potential for clinical impact in the coming decades, when such interventions are likely to be critically important.The review focuses on this problem from an interdisciplinary perspective, including basic science innovations and best practice in infectious disease. Cite this article: Moriarty TF, Kuehl R, Coenye T, et al. Orthopaedic device related infection: current and future interventions for improved prevention and treatment. EFORT Open Rev 2016;1:89-99. DOI: 10.1302/2058-5241.1.000037.

Phage and Yeast Display

Despite the availability of antimicrobial drugs, the continued development of microbial resistance--established through escape mutations and the emergence of resistant strains--limits their clinical utility. The discovery of novel, therapeutic, monoclonal antibodies (mAbs) offers viable clinical alternatives in the treatment and prophylaxis of infectious diseases. Human mAb-based therapies are typically nontoxic in patients and demonstrate high specificity for the intended microbial target. This specificity prevents negative impacts on the patient microbiome and avoids driving the resistance of nontarget species. The in vitro selection of human antibody fragment libraries displayed on phage or yeast surfaces represents a group of well-established technologies capable of generating human mAbs. The advantage of these forms of microbial display is the large repertoire of human antibody fragments present during a single selection campaign. Furthermore, the in vitro selection environments of microbial surface display allow for the rapid isolation of antibodies--and their encoding genes--against infectious pathogens and their toxins that are impractical within in vivo systems, such as murine hybridomas. This article focuses on the technologies of phage display and yeast display, as these strategies relate to the discovery of human mAbs for the treatment and vaccine development of infectious diseases.

Successful selection of an infection-protective anti-Staphylococcus aureus monoclonal antibody and its protective activity in murine infection models

Recent clinical trials to develop anti-methicillin-resistant Staphylococcus aureus (MRSA) therapeutic antibodies have met unsuccessful sequels. To develop more effective antibodies against MRSA infection, a panel of mAbs against S. aureus cell wall was generated and then screened for the most protective mAb in mouse infection models. Twenty-two anti-S. aureus IgG mAbs were obtained from mice that had been immunized with alkali-processed, deacetylated cell walls of S. aureus. One of these mAbs, ZBIA5H, exhibited life-saving effects in mouse models of sepsis caused by community-acquired MRSA strain MW2 and vancomycin-resistant S. aureus strain VRS1. It also had a curative effect in a MW2-caused pneumonia model. Curiously, the target of ZBIA5H was considered to be a conformational epitope of either the 1,4-β-linkage between N-acetylmuramic acid and N-acetyl-D-glucosamine or the peptidoglycan per se. Reactivity of ZBIA5H to S. aureus whole cells or purified peptidoglycan was weaker than that of most of the other mAbs generated in this study. However, the latter mAbs did not have the protective activities against S. aureus that ZBIA5H did. These data indicate that the epitopes that trigger production of high-yield and/or high-affinity antibodies may not be the most suitable epitopes for developing anti-infective antibodies. ZBIA5H or its humanized form may find a future clinical application, and its target epitope may be used for the production of vaccines against S. aureus infection.

Antibody-Based Biologics and Their Promise to Combat Staphylococcus aureus Infections

The growing incidence of serious infections mediated by methicillin-resistant Staphylococcus aureus (MRSA) strains poses a significant risk to public health. This risk is exacerbated by a prolonged void in the discovery and development of truly novel antibiotics and the absence of a vaccine. These gaps have created renewed interest in the use of biologics in the prevention and treatment of serious staphylococcal infections. In this review, we focus on efforts towards the discovery and development of antibody-based biologic agents and their potential as clinical agents in the management of serious S. aureus infections. Recent promising data for monoclonal antibodies (mAbs) targeting anthrax and Ebola highlight the potential of antibody-based biologics as therapeutic agents for serious infections.

Worldwide Population Structure, Long-Term Demography, and Local Adaptation of Helicobacter pylori

Helicobacter pylori is an important human pathogen associated with serious gastric diseases. Owing to its medical importance and close relationship with its human host, understanding genomic patterns of global and local adaptation in H. pylori may be of particular significance for both clinical and evolutionary studies. Here we present the first such whole genome analysis of 60 globally distributed strains, from which we inferred worldwide population structure and demographic history and shed light on interesting global and local events of positive selection, with particular emphasis on the evolution of San-associated lineages. Our results indicate a more ancient origin for the association of humans and H. pylori than previously thought. We identify several important perspectives for future clinical research on candidate selected regions that include both previously characterized genes (e.g., transcription elongation factor NusA and tumor necrosis factor alpha-inducing protein Tipα) and hitherto unknown functional genes.

Amidase, a cell wall hydrolase, elicits protective immunity against Staphylococcus aureus and S. epidermidis

The morbidity and the mortality associated with Staphylococcus aureus and S. epidermidis infections have greatly increased due to the rapid emergence of highly virulent and antibiotic resistant strains. Development of a vaccine-based therapy is greatly desired. However, no staphylococcal vaccine is available till date. In this study, we have identified Major amidase (Atl-AM) as a prime candidate for future vaccine design against these pathogens. Atl-AM is a multi-functional non-covalently cell wall associated protein which is involved in staphylococcal cell separation after cell division, host extracellular matrix adhesion and biofilm formation. Atl-AM is present on the surface of diverse S. aureus and S. epidermidis strains. When used in combination with Freund's adjuvant, Atl-AM generated a mixed Th1 and Th2 mediated immune response which is skewed more toward Th1; and showed increased production of opsonophagocytic IgG2a and IgG2b antibodies. Significant protective immune response was observed when vaccinated mice were challenged with S. aureus or S. epidermidis. Vaccination prevented the systemic dissemination of both organisms. Our results demonstrate the remarkable efficacy of Atl-AM as a vaccine candidate against both of these pathogens.

X-ray CT and pneumonia inhibition properties of gold-silver nanoparticles for targeting MRSA induced pneumonia

Non-invasive assay for the early stage diagnosis of methicillin resistant Staphylococcus aureus (MRSA) related pneumonia is of great clinical importance and still a great challenge. In this paper, we reported a novel kind of Au@Ag core-shell theranostic nanoparticles (NPs) conjugated with MRSA specific antibody on their surface. Compared with the raw Au@Ag NPs, these antibody modified NPs (AAMA NPs) showed 10.66 fold enhancement targeting to the MRSA in vitro. In vivo target efficacy was measured with rats bearing pneumonia induced by different pathogens. Computed tomography (CT) results revealed that these AAMA NPs had higher CT contrast enhancement (498 HU), than those of raw Au@Ag and Omnipaque (oth <100 HU). In addition, lesions labeled by AAMA NPs could be distinguished from lung parenchyma by taking advantage of spectra CT. Bio-distribution analysis confirmed that these AAMA NPs accumulated in the MRSA rich site. Both BAL and Elisa assays indicated that these AAMA NPs greatly alleviated the inflammation reaction by reducing bacterial proliferation and cytokine production. Pathological study showed that these NPs exerted negligible long term cytotoxicity in vivo.

Models matter: the search for an effective Staphylococcus aureus vaccine

Staphylococcus aureus is a highly successful bacterial pathogen owing to its abundance of cell surface and secreted virulence factors. It is estimated that 30% of the population is colonized with S. aureus, usually on mucosal surfaces, and methicillin-resistant S. aureus is a major public health concern. There have been multiple attempts to develop an S. aureus vaccine using one or more cell surface virulence factors as antigens; all of these vaccine trials have failed. In this Opinion article, we suggest that an over-reliance on rodent models and a focus on targeting cell surface components have been major contributing factors to this failure.

Phenol-soluble modulins and staphylococcal infection

Staphylococcus aureus is an important human pathogen and a leading cause of death worldwide. Phenol-soluble modulins (PSMs) have recently emerged as a novel toxin family defining the virulence potential of highly aggressive S. aureus isolates. PSMs have multiple roles in staphylococcal pathogenesis, causing lysis of red and white blood cells, stimulating inflammatory responses and contributing to biofilm development and the dissemination of biofilm-associated infections. Moreover, the pronounced capacity of PSMs to kill human neutrophils after phagocytosis might explain failures in the development of anti-staphylococcal vaccines. Here, we discuss recent progress made in our understanding of the biochemical and genetic properties of PSMs and their role in S. aureus pathogenesis, and suggest potential avenues to target PSMs for the development of anti-staphylococcal drugs.

Will there ever be a universal Staphylococcus aureus vaccine?

Developing a universal vaccine for S. aureus is a top priority but to date we have only had failures in human clinical trials. Given the plethora of bacterial virulence factors, broad range of the health of humans at-risk for infections, lack of any information regarding immune effectors mediating protection for any manifestation of S. aureus infection and overall competence of this organism as a colonizer, commensal and pathogen, we may just simply have to accept the fact that we will not get a universal vaccine. Antigenic variation is a major challenge for some vaccine targets and for many conserved targets the organism can easily decrease or even eliminate expression to avoid immune effectors without compromise to infectivity and ability to cause disease. Studies of human immune responses similarly have been unable to identify any clear mediators of immunity and data from such studies can only eliminate those found not to be associated with protection or that might serve as a marker for individuals with a higher level of resistance to infection. Animal studies are not predictive of success in humans and unlikely will be except in hindsight if and when we develop an efficacious vaccine. Successful vaccines for other bacteria based on capsular polysaccharides have not worked to date for S. aureus, and laboratory studies combining antibody to the major capsular serotypes and the other S. aureus surface polysaccharide, poly-N-acetyl glucosamine, unexpectedly showed interference not augmentation of immunity. Potential pathways toward vaccine development do exist but for the foreseeable future will be based on empiric approaches derived from laboratory-based in vitro and animal tests and not on inducing a known immune effector that predicts human resistance to infection.

Challenges for a universal Staphylococcus aureus vaccine

This review considers the reasons why the staphylococcal vaccine trials may have failed, based on new information about protective immunity against Staphylococcus aureus. The clinical trials and future vaccine candidate antigens are reviewed. Challenges facing the development of a universal S. aureus vaccine are also considered. The lack of a biomarker that is able to predict protection is a major stumbling block in the development of a staphylococcal vaccine. The major new information involves the role of cell-mediated immunity, specifically T-helper 17 cells and interleukin 17, as well as the lack of protection afforded by specific antibodies. This has major implications for future vaccine development and planning of clinical trials.

Immunization with Staphylococcus aureus iron regulated surface determinant B (IsdB) confers protection via Th17/IL17 pathway in a murine sepsis model

We have previously shown that IsdB, a conserved protein expressed by Staphylococcus aureus, induces a robust antibody response which correlates with protection in a murine challenge model. Here we investigate the role of cellular immunity in IsdB mediated protection using lymphocyte deficient SCID mice. As opposed to WT CB-17 mice the CB-17 SCID mice were not protected against a lethal challenge of S. aureus after active and passive immunizations with IsdB. Adoptive transfer of in vitro isolated lymphocyte subsets revealed that reconstituting mice with IsdB specific CD3+ or CD4+ T-cells conferred antigen specific protection while CD8⁺ T-cells, CD19⁺ B-cells and plasma cells (CD138^highB220^intCD19^lo) alone were not protective. A combination of CD3⁺ T-cells plus CD19⁺ B-cells conferred protection in CB-17 SCID mice, whereas bovine serum albumin (BSA) immune lymphocytes did not confer protection. Active immunization experiments indicated that IsdB immunized Jh mice (B-cell deficient) were protected against lethal challenge, while nude (T-cell deficient) mice were not. In vitro assays indicated that isolated IsdB specific splenocytes from immunized mice produced abundant IL-17A, much less IFN-γ and no detectable IL-4. IL-23 deficient mice were not protected from a lethal challenge by IsdB vaccination, pointing to a critical role for CD4⁺ Th17 in IsdB-mediated vaccination. Neutralizing IL-17A, but not IL-22 in vivo significantly increased mortality in IsdB immunized mice; whereas, neutralizing IFN-γ did not alter IsdB-mediated protection. These findings suggest that IL-17A producing Th17 cells play an essential role in IsdB vaccine-mediated defense against invasive S. aureus infection in mice.

Is there a future for a Staphylococcus aureus vaccine?

Multiple attempts to develop a vaccine to prevent Staphylococcus aureus infections have failed. To date, all have been based upon the development of opsonic antibodies. New information suggests that cell mediated immunity may be critical for protection against S. aureus infections. The arm of the immune system that provides the protection contains the Th17/IL-17 axis. Th17 cells release IL-17, which are important for mobilization and activation of neutrophils. Naturally, antibodies aid the neutrophils in the uptake and killing of staphylococci, but immune globulin does not seem to be sufficient to afford protection. New approaches that focus on Th17/IL-17 may allow for the development of a successful S. aureus vaccine.

Immunotherapeutic approaches against Staphylococcus aureus

Staphylococcus aureus is a major cause of life-threatening infections such as bacteremia and endocarditis. Unfortunately, many strains of this bacterial species have become resistant to certain antibiotics, including methicillin and amoxicillin. These strains are known as methicillin-resistant S. aureus (MRSA). Therefore, the prophylactic and therapeutic potential of antistaphylococcal vaccines is currently being explored with priority. In animal models, (passive) immunization with (antibodies directed against) certain S. aureus surface components, staphylococcal toxins and capsular polysaccharides protects against S. aureus colonization or infection. However, immunization studies performed in humans show less promising results. So far, not a single antistaphylococcal vaccine successfully passed clinical trials. This article focuses on the results that were obtained with immunotherapeutic approaches directed against S. aureus in animal and human studies. In addition, it is discussed whether effective immunization approaches against S. aureus are feasible in humans.

Serodiversity of opsonic antibodies against Enterococcus faecalis--glycans of the cell wall revisited

In a typing system based on opsonic antibodies against carbohydrate antigens of the cell envelope, 60% of Enterococcus faecalis strains can be assigned to one of four serotypes (CPS-A to CPS-D). The structural basis for enterococcal serotypes, however, is still incompletely understood. Here we demonstrate that antibodies raised against lipoteichoic acid (LTA) from a CPS-A strain are opsonic to both CPS-A and CPS-B strains. LTA-specific antibodies also bind to LTA of CPS-C and CPS-D strains, but fail to opsonize them. From CPS-C and CPS-D strains resistant to opsonization by anti-LTA, we purified a novel diheteroglycan with a repeating unit of →6)-β-Galf-(1→3)- β-D-Glcp-(1→ with O-acetylation in position 5 and lactic acid substitution at position 3 of the Galf residue. The purified diheteroglycan, but not LTA absorbed opsonic antibodies from whole cell antiserum against E. faecalis type 2 (a CPS-C strain) and type 5 (CPS-D). Rabbit antiserum raised against purified diheteroglycan opsonized CPS-C and CPS-D strains and passive protection with diheteroglycan-specific antiserum reduced bacterial counts by 1.4-3.4 logs in mice infected with E. faecalis strains of the CPS-C and CPS-D serotype. Diheteroglycan-specific opsonic antibodies were absorbed by whole bacterial cells of E. faecalis FA2-2 (CPS-C) but not by its isogenic acapsular cpsI-mutant and on native PAGE purified diheteroglycan co-migrated with the gene product of the cps-locus, suggesting that it is synthesized by this locus. In summary, two polysaccharide antigens, LTA and a novel diheteroglycan, are targets of opsonic antibodies against typeable E. faecalis strains. These cell-wall associated polymers are promising candidates for active and passive vaccination and add to our armamentarium to fight this important nosocomial pathogen.

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.

An integrated approach to epitope analysis II: A system for proteomic-scale prediction of immunological characteristics

Background

Improving our understanding of the immune response is fundamental to developing strategies to combat a wide range of diseases. We describe an integrated epitope analysis system which is based on principal component analysis of sequences of amino acids, using a multilayer perceptron neural net to conduct QSAR regression predictions for peptide binding affinities to 35 MHC-I and 14 MHC-II alleles.

Results

The approach described allows rapid processing of single proteins, entire proteomes or subsets thereof, as well as multiple strains of the same organism. It enables consideration of the interface of diversity of both microorganisms and of host immunogenetics. Patterns of binding affinity are linked to topological features, such as extracellular or intramembrane location, and integrated into a graphical display which facilitates conceptual understanding of the interplay of B-cell and T-cell mediated immunity.

Patterns which emerge from application of this approach include the correlations between peptides showing high affinity binding to MHC-I and to MHC-II, and also with predicted B-cell epitopes. These are characterized as coincident epitope groups (CEGs). Also evident are long range patterns across proteins which identify regions of high affinity binding for a permuted population of diverse and heterozygous HLA alleles, as well as subtle differences in reactions with MHCs of individual HLA alleles, which may be important in disease susceptibility, and in vaccine and clinical trial design. Comparisons are shown of predicted epitope mapping derived from application of the QSAR approach with experimentally derived epitope maps from a diverse multi-species dataset, from Staphylococcus aureus, and from vaccinia virus.

Conclusions

A desktop application with interactive graphic capability is shown to be a useful platform for development of prediction and visualization tools for epitope mapping at scales ranging from individual proteins to proteomes from multiple strains of an organism. The possible functional implications of the patterns of peptide epitopes observed are discussed, including their implications for B-cell and T-cell cooperation and cross presentation.

Functional antibodies targeting IsaA of Staphylococcus aureus augment host immune response and open new perspectives for antibacterial therapy

Staphylococcus aureus is the most common cause of nosocomial infections. Multiple antibiotic resistance and severe clinical outcomes provide a strong rationale for development of immunoglobulin-based strategies. Traditionally, novel immunological approaches against bacterial pathogens involve antibodies directed against cell surface-exposed virulence-associated epitopes or toxins. In this study, we generated a monoclonal antibody targeting the housekeeping protein IsaA, a suggested soluble lytic transglycosylase of S. aureus, and tested its therapeutic efficacy in two experimental mouse infection models. A murine anti-IsaA antibody of the IgG1 subclass (UK-66P) showed the highest binding affinity in Biacore analysis. This antibody recognized all S. aureus strains tested, including hospital-acquired and community-acquired methicillin-resistant S. aureus strains. Therapeutic efficacy in vivo in mice was analyzed using a central venous catheter-related infection model and a sepsis survival model. In both models, anti-IsaA IgG1 conferred protection against staphylococcal infection. Ex vivo, UK-66P activates professional phagocytes and induces highly microbicidal reactive oxygen metabolites in a dose-dependent manner, resulting in bacterial killing. The study provides proof of concept that monoclonal IgG1 antibodies with high affinity to the ubiquitously expressed, single-epitope-targeting IsaA are effective in the treatment of staphylococcal infection in different mouse models. Anti-IsaA antibodies might be a useful component in an antibody-based therapeutic for prophylaxis or adjunctive treatment of human cases of S. aureus infections.

Eradication of drug resistant Staphylococcus aureus by liposomal oleic acids

Staphylococcus aureus (S. aureus) represents a major threat to a broad range of healthcare and community associated infections. This bacterium has rapidly evolved resistance to multiple drugs throughout its antibiotic history and thus it is imperative to develop novel antimicrobial strategies to enrich the currently shrinking therapeutic options against S. aureus. This study evaluated the antimicrobial activity and therapeutic efficacy of oleic acid (OA) in a liposomal formulation as an innate bactericide against methicillin-resistant S. aureus (MRSA). In vitro studies showed that these OA-loaded liposomes (LipoOA) could rapidly fuse into the bacterial membranes, thereby significantly improving the potency of OA to kill MRSA compared with the use of free OA. Further in vivo tests demonstrated that LipoOA were highly effective in curing skin infections caused by MRSA bacteria and preserving the integrity of the infected skin using a mouse skin model. Moreover, a preliminary skin toxicity study proved high biocompatibility of LipoOA to normal skin tissues. These findings suggest that LipoOA hold great potential to become a new, effective, and safe antimicrobial agent for the treatment of MRSA infections.

Progress in the development of effective vaccines to prevent selected gram-positive bacterial infections

Infections caused by virulent Gram-positive bacteria, such as Staphylococcus aureus, group B streptococci and group A streptococci, remain significant causes of morbidity and mortality despite progress in antimicrobial therapy. Despite significant advances in the understanding of the pathogenesis of infection caused by these organisms, there are only limited strategies to prevent infection. In this article, we review efforts to develop safe and effective vaccines that would prevent infections caused by these 3 pathogens.

Novel targeted immunotherapy approaches for staphylococcal infection

IMPORTANCE OF THE FIELD

Staphylococcus aureus is a leading human pathogen in the hospital and the community. Many S. aureus strains are resistant to antibiotics, making treatment of S. aureus infections often very complicated. In contrast to many other bacterial pathogens, a working vaccine has never been found for S. aureus despite considerable efforts in academia and pharmaceutical companies.

AREAS COVERED IN THIS REVIEW

The latest strategies aimed at finding a working vaccine against S. aureus, including active and passive immunization efforts in pre-clinical and clinical stages, and the molecular reasons for why it may be difficult to develop a vaccine are discussed.

WHAT THE READER WILL GAIN

In addition to receiving an overview of current efforts in S. aureus vaccine research, the reader will understand that vaccine development for S. aureus may be difficult owing to the facts that S. aureus is a commensal microorganism and produces toxins that lyse white blood cells, thereby undermining a vaccine's role as a facilitator of opsonophagocytosis.

TAKE HOME MESSAGE

As a result of failed clinical trials with monovalent traditional vaccines, recent developments include a shift towards the potential use of polyvalent formulas and therapeutic antibodies and more systematic selection of optimal antigens.

Surmounting antimicrobial resistance in the Millennium Superbug: Staphylococcus aureus

Staphylococcus aureus is the third most dreaded pathogen posing a severe threat due to its refractory behavior against the current armamentarium of antimicrobial drugs. This is attributed to the evolution of an array of resistance mechanisms responsible for morbidity and mortality globally. Local and international travel has resulted in the movement of drug resistant S. aureus clones from hospitals into communities and further into different geographical areas where they have been responsible for epidemic outbreaks. Thus, there is a dire necessity to refrain further cross movement of these multidrug resistant clones across the globe. The plausible alternative to prevent this situation is by thorough implementation of regulatory aspects of sanitation, formulary usage and development of new therapeutic interventions. Various strategies like exploring novel antibacterial targets, high throughput screening of microbes, combinatorial and synthetic chemistry, combinatorial biosynthesis and vaccine development are being extensively sought to overcome multidrug resistant chronic Staphylococcal infections. The majority of the antibacterial drugs are of microbial origin and are prone to being resisted. Anti-staphylococcal plant natural products that may provide a new alternative to overcome the refractory S.aureus under clinical settings have grossly been unnoticed. The present communication highlights the new chemical entities and therapeutic modalities that are entering the pharmaceutical market or are in the late stages of clinical evaluation to overcome multidrug resistant Staphylococcal infections. The review also explores the possibility of immunity and enzyme-based interventions as new therapeutic modalities and highlights the regulatory concerns on the prescription, usage and formulary development in the developed and developing world to keep the new chemical entities and therapeutic modalities viable to overcome antimicrobial resistance in S. aureus.

The antigenome: from protein subunit vaccines to antibody treatments of bacterial infections?

New strategies are needed to master infectious diseases. The so-called "passive vaccination", i.e., prevention and treatment with specific antibodies, has a proven record and potential in the management of infections and entered the medical arena more than 100 years ago. Progress in the identification of specific antigens has become the hallmark in the development of novel subunit vaccines that often contain only a single immunogen, frequently proteins, derived from the microbe in order to induce protective immunity. On the other hand, the monoclonal antibody technology has enabled biotechnology to produce antibody species in unlimited quantities and at reasonable costs that are more or less identical to their human counterparts and bind with high affinity to only one specific site of a given antigen. Although, this technology has provided a robust platform for launching novel and successful treatments against a variety of devastating diseases, it is up till now only exceptionally employed in therapy of infectious diseases. Monoclonal antibodies engaged in the treatment of specific cancers seem to work by a dual mode; they mark the cancerous cells for decontamination by the immune system, but also block a function that intervenes with cell growth. The availability of the entire genome sequence of pathogens has strongly facilitated the identification of highly specific protein antigens that are suitable targets for neutralizing antibodies, but also often seem to play an important role in the microbe's life cycle. Thus, the growing repertoire of well-characterized protein antigens will open the perspective to develop monoclonal antibodies against bacterial infections, at least as last resort treatment, when vaccination and antibiotics are no options for prevention or therapy. In the following chapter we describe and compare various technologies regarding the identification of suitable target antigens and the foundation of cognate monoclonal antibodies and discuss their possible applications in the treatment of bacterial infections together with an overview of current efforts.

Selection and characterization of murine monoclonal antibodies to Staphylococcus aureus iron-regulated surface determinant B with functional activity in vitro and in vivo

In an effort to characterize important epitopes of Staphylococcus aureus iron-regulated surface determinant B (IsdB), murine IsdB-specific monoclonal antibodies (MAbs) were isolated and characterized. A panel of 12 MAbs was isolated. All 12 MAbs recognized IsdB in enzyme-linked immunosorbent assays and Western blots; 10 recognized native IsdB expressed by S. aureus. The antigen epitope binding of eight of the MAbs was examined further. Three methods were used to assess binding diversity: MAb binding to IsdB muteins, pairwise binding to recombinant IsdB, and pairwise binding to IsdB-expressing bacteria. Data from these analyses indicated that MAbs could be grouped based on distinct or nonoverlapping epitope recognition. Also, MAb binding to recombinant IsdB required a significant portion of intact antigen, implying conformational epitope recognition. Four MAbs with nonoverlapping epitopes were evaluated for in vitro opsonophagocytic killing (OPK) activity and efficacy in murine challenge models. These were isotype switched from immunoglobulin G1 (IgG1) to IgG2b to potentially enhance activity; however, this isotype switch did not appear to enhance functional activity. MAb 2H2 exhibited OPK activity (> or =50% killing in the in vitro OPK assay) and was protective in two lethal challenge models and a sublethal indwelling catheter model. MAb 13C7 did not exhibit OPK (<50% killing in the in vitro assay) and was protective in one lethal challenge model. Neither MAb 13G11 nor MAb 1G3 exhibited OPK activity in vitro or was active in a lethal challenge model. The data suggest that several nonoverlapping epitopes are recognized by the IsdB-specific MAbs, but not all of these epitopes induce protective antibodies.

Progress towards recombinant anti-infective antibodies

The global market for monoclonal antibody therapeutics reached a total of $11.2 billion in 2004, with an impressive 42% growth rate over the previous five years and is expected to reach approximately $34 billion by 2010. Coupled with this growth are stream-lined product development, production scale-up and regulatory approval processes for the highly conserved antibody structure. While only one of the 21 current FDA-approved antibodies, and one of the 38 products in advanced clinical trials target infectious diseases, there is increasing academic, government and commercial interest in this area. Synagis, an antibody neutralizing respiratory syncitial virus (RSV), garnered impressive sales of $1.1 billion in 2006 in spite of its high cost and undocumented effects on viral titres in human patients. The success of anti-RSV passive immunization has motivated the continued development of anti-infectives to treat a number of other infectious diseases, including those mediated by viruses, toxins and bacterial/ fungal cells. Concurrently, advances in antibody technology suggest that cocktails of several monoclonal antibodies with unique epitope specificity or single monoclonal antibodies with broad serotype specificity may be the most successful format. Recent patents and patent applications in these areas will be discussed as predictors of future anti-infective therapeutics.

Staphylococcal vaccines and immunotherapies

Staphylococcus aureus is an important pathogen in the hospital and in the community, and it is increasingly resistant to multiple antibiotics. A nonantimicrobial approach to controlling S aureus is needed. The most extensively tested vaccine against S aureus, which is a capsular polysaccharide-based vaccine known as StaphVAX, showed promise in an initial phase 3 trial, but was found to be ineffective in a confirmatory trial, leading to its development being halted. Likewise, a human IgG preparation known as INH-A21 (Veronate) with elevated levels of antibodies to the staphylococcal surface adhesins ClfA and SdrG made it into phase 3 testing, where it failed to show a clinical benefit. Several novel antigens are being tested for potential inclusion in a staphylococcal vaccine, including cell wall-anchored adhesin proteins and exotoxins. Given the multiple and sometimes redundant virulence factors of S aureus that enable it to be such a crafty pathogen, if a vaccine is to prove effective, it will have to be multicomponent, incorporating several surface proteins, toxoids, and surface polysaccharides.

Anti-infective antibodies: a novel tool to prevent and treat nosocomial diseases

The emergence of multidrug-resistant bacteria is a growing challenge for healthcare in the treatment of infectious diseases. In particular, nosocomial infections are getting out of control and reduce the likelihood to recover without, sometimes lethal, complications and long-term damage. Current antibiotics are unable to keep nosocomial infections in check and novel ones move only reluctantly forward and are expected to only delay the problem of multidrug resistance. Progress made in the identification of suitable pathogen targets, a better understanding of host-parasite interactions and the recent inclusion of monoclonal antibodies into the arsenal of novel therapies has provoked the interest to revitalize a historical concept of medicine to treat and prevent bacterial infections with antibodies.

Novel targets for antibiotics in Staphylococcus aureus

Multiple resistant staphylococci that cause significant morbidity and mortality are the leading cause of nosocomial infections. Meanwhile, methicillin-resistant Staphylococcus aureus (MRSA) also spreads in the community, where highly virulent strains infect children and young adults who have no predisposing risk factors. Although some treatment options remain, the search for new antibacterial targets and lead compounds is urgently required to ensure that staphylococcal infections can be effectively treated in the future. Promising targets for new antibacterials are gene products that are involved in essential cell functions. In addition to antibacterials, active and passive immunization strategies are being developed that target surface components of staphylococci such as cell wall-linked adhesins, teichoic acids and capsule or immunodominant antigens.

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.