Biologic properties and vaccine potential of the staphylococcal poly-N-acetyl glucosamine surface polysaccharide

Glycoconjugate vaccines against antimicrobial resistant pathogens

INTRODUCTION

Antimicrobial resistance (AMR) is responsible for the death of millions worldwide and stands as a major threat to our healthcare systems, which are heavily reliant on antibiotics to fight bacterial infections. The development of vaccines against the main pathogens involved is urgently required as prevention remains essential against the rise of AMR.

AREAS COVERED

A systematic research review was conducted on MEDLINE database focusing on the six AMR pathogens defined as ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli), which are considered critical or high priority pathogens by the World Health Organization (WHO) and the Centers for Disease Control and Prevention (CDC). The analysis was intersecated with the terms carbohydrate, glycoconjugate, bioconjugate, glyconanoparticle, and multiple presenting antigen system vaccines.

EXPERT OPINION

Glycoconjugate vaccines have been successful in preventing meningitis and pneumoniae, and there are high expectations that they will play a key role in fighting AMR. We herein discuss the recent technological, preclinical, and clinical advances, as well as the challenges associated with the development of carbohydrate-based vaccines against leading AMR bacteria, with focus on the ESKAPE pathogens. The need of innovative clinical and regulatory approaches to tackle these targets is also highlighted.

Current treatments for biofilm-associated periprosthetic joint infection and new potential strategies

Periprosthetic joint infection (PJI) remains a devastating complication after total joint arthroplasty. Bacteria involved in these infections are notorious for adhering to foreign implanted surfaces and generating a biofilm matrix. These biofilms protect the bacteria from antibiotic treatment and the immune system making eradication difficult. Current treatment strategies including debridement, antibiotics, and implant retention, and one- and two-stage revisions still present a relatively high overall failure rate. One of the main shortcomings that has been associated with this high failure rate is the lack of a robust approach to treating bacterial biofilm. Therefore, in this review, we will highlight new strategies that have the potential to combat PJI by targeting biofilm integrity, therefore giving antibiotics and the immune system access to the internal network of the biofilm structure. This combination antibiofilm/antibiotic therapy may be a new strategy for PJI treatment while promoting implant retention.

Staphylococcus aureus: biofilm formation and strategies against it

The formation of Staphylococcus aureus biofilm causes significant infections in the human body. Biofilm forms through the aggregation of bacterial species and brings about many complications. It mediates drug resistance and persistence and facilitates the recurrence of infection at the end of antimicrobial therapy. Biofilm formation goes through a series of steps to complete, and any interference in these steps can disrupt its formation. Such interference may occur at any stage of biofilm production, including attachment, monolayer formation, and accumulation. Interfering agents can act as quorum sensing inhibitors and interfere in the functionality of quorum sensing receptors, attachment inhibitors and affect the cell hydrophobicity. Among these inhibiting strategies, attachment inhibitors could serve as the best agents against biofilm formation. If pathogens abort the attachment, the following stages of biofilm formation, e.g., accumulation and dispersion, will fail to materialize. Inhibition at this stage leads to suppression of virulence factors and invasion. One of the best-known inhibitors is a chelator that collects metal, Fe+, Zn+, and magnesium critical for biofilm formation. These influential factors in the binding and formation of biofilm are investigated, and the coping strategy is discussed. This review examines the stages of biofilm formation and determines what factors interfere in the continuity of these steps. Finally, the inhibition strategies are investigated, reviewed, and discussed. Keywords: Biofilm, Staphylococcus, Biofilm inhibitor, Dispersion, Antibiofilm agent, EPS, PIA.

Glycomics Microarrays Reveal Differential In Situ Presentation of the Biofilm Polysaccharide Poly-N-acetylglucosamine on Acinetobacter baumannii and Staphylococcus aureus Cell Surfaces

The biofilm component poly-N-acetylglucosamine (PNAG) is an important virulence determinant in medical-device-related infections caused by ESKAPE group pathogens including Gram-positive Staphylococcus aureus and Gram-negative Acinetobacter baumannii. PNAG presentation on bacterial cell surfaces and its accessibility for host interactions are not fully understood. We employed a lectin microarray to examine PNAG surface presentation and interactions on methicillin-sensitive (MSSA) and methicillin-resistant S. aureus (MRSA) and a clinical A. baumannii isolate. Purified PNAG bound to wheatgerm agglutinin (WGA) and succinylated WGA (sWGA) lectins only. PNAG was the main accessible surface component on MSSA but was relatively inaccessible on the A. baumannii surface, where it modulated the presentation of other surface molecules. Carbohydrate microarrays demonstrated similar specificities of S. aureus and A. baumannii for their most intensely binding carbohydrates, including 3' and 6'sialyllactose, but differences in moderately binding ligands, including blood groups A and B. An N-acetylglucosamine-binding lectin function which binds to PNAG identified on the A. baumannii cell surface may contribute to biofilm structure and PNAG surface presentation on A. baumannii. Overall, these data indicated differences in PNAG presentation and accessibility for interactions on Gram-positive and Gram-negative cell surfaces which may play an important role in biofilm-mediated pathogenesis.

Immunization against poly-N-acetylglucosamine reduces neutrophil activation and GVHD while sparing microbial diversity

Microbial invasion into the intestinal mucosa after allogeneic hematopoietic cell transplantation (allo-HCT) triggers neutrophil activation and requires antibiotic interventions to prevent sepsis. However, antibiotics lead to a loss of microbiota diversity, which is connected to a higher incidence of acute graft-versus-host disease (aGVHD). Antimicrobial therapies that eliminate invading bacteria and reduce neutrophil-mediated damage without reducing the diversity of the microbiota are therefore highly desirable. A potential solution would be the use of antimicrobial antibodies that target invading pathogens, ultimately leading to their elimination by innate immune cells. In a mouse model of aGVHD, we investigated the potency of active and passive immunization against the conserved microbial surface polysaccharide poly-N-acetylglucosamine (PNAG) that is expressed on numerous pathogens. Treatment with monoclonal or polyclonal antibodies to PNAG (anti-PNAG) or vaccination against PNAG reduced aGVHD-related mortality. Anti-PNAG treatment did not change the intestinal microbial diversity as determined by 16S ribosomal DNA sequencing. Anti-PNAG treatment reduced myeloperoxidase activation and proliferation of neutrophil granulocytes (neutrophils) in the ileum of mice developing GVHD. In vitro, anti-PNAG treatment showed high antimicrobial activity. The functional role of neutrophils was confirmed by using neutrophil-deficient LysM ^cre Mcl1 ^fl/fl mice that had no survival advantage under anti-PNAG treatment. In summary, the control of invading bacteria by anti-PNAG treatment could be a novel approach to reduce the uncontrolled neutrophil activation that promotes early GVHD and opens a new avenue to interfere with aGVHD without affecting commensal intestinal microbial diversity.

Potential targets for next generation antimicrobial glycoconjugate vaccines

Cell surface carbohydrates have been proven optimal targets for vaccine development. Conjugation of polysaccharides to a carrier protein triggers a T-cell-dependent immune response to the glycan moiety. Licensed glycoconjugate vaccines are produced by chemical conjugation of capsular polysaccharides to prevent meningitis caused by meningococcus, pneumococcus and Haemophilus influenzae type b. However, other classes of carbohydrates (O-antigens, exopolysaccharides, wall/teichoic acids) represent attractive targets for developing vaccines. Recent analysis from WHO/CHO underpins alarming concern toward antibiotic-resistant bacteria, such as the so called ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Enterobacter spp.) and additional pathogens such as Clostridium difficile and Group A Streptococcus. Fungal infections are also becoming increasingly invasive for immunocompromised patients or hospitalized individuals. Other emergencies could derive from bacteria which spread during environmental calamities (Vibrio cholerae) or with potential as bioterrorism weapons (Burkholderia pseudomallei and mallei, Francisella tularensis). Vaccination could aid reducing the use of broad-spectrum antibiotics and provide protection by herd immunity also to individuals who are not vaccinated.

This review analyzes structural and functional differences of the polysaccharides exposed on the surface of emerging pathogenic bacteria, combined with medical need and technological feasibility of corresponding glycoconjugate vaccines.

Structural investigation of human S. aureus-targeting antibodies that bind wall teichoic acid

Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) are a growing health threat worldwide. Efforts to identify novel antibodies that target S. aureus cell surface antigens are a promising direction in the development of antibiotics that can halt MRSA infection. We biochemically and structurally characterized three patient-derived MRSA-targeting antibodies that bind to wall teichoic acid (WTA), which is a polyanionic surface glycopolymer. In S. aureus, WTA exists in both α- and β-forms, based on the stereochemistry of attachment of a N-acetylglucosamine residue to the repeating phosphoribitol sugar unit. We identified a panel of antibodies cloned from human patients that specifically recognize the α or β form of WTA, and can bind with high affinity to pathogenic wild-type strains of S. aureus bacteria. To investigate how the β-WTA specific antibodies interact with their target epitope, we determined the X-ray crystal structures of the three β-WTA specific antibodies, 4462, 4497, and 6078 (Protein Data Bank IDs 6DWI, 6DWA, and 6DW2, respectively), bound to a synthetic WTA epitope. These structures reveal that all three of these antibodies, while utilizing distinct antibody complementarity-determining region sequences and conformations to interact with β-WTA, fulfill two recognition principles: binding to the β-GlcNAc pyranose core and triangulation of WTA phosphate residues with polar contacts. These studies reveal the molecular basis for targeting a unique S. aureus cell surface epitope and highlight the power of human patient-based antibody discovery techniques for finding novel pathogen-targeting therapeutics.

Antibody to Poly-N-acetyl glucosamine provides protection against intracellular pathogens: Mechanism of action and validation in horse foals challenged with Rhodococcus equi

Immune correlates of protection against intracellular bacterial pathogens are largely thought to be cell-mediated, although a reasonable amount of data supports a role for antibody-mediated protection. To define a role for antibody-mediated immunity against an intracellular pathogen, Rhodococcus equi, that causes granulomatous pneumonia in horse foals, we devised and tested an experimental system relying solely on antibody-mediated protection against this host-specific etiologic agent. Immunity was induced by vaccinating pregnant mares 6 and 3 weeks prior to predicted parturition with a conjugate vaccine targeting the highly conserved microbial surface polysaccharide, poly-N-acetyl glucosamine (PNAG). We ascertained antibody was transferred to foals via colostrum, the only means for foals to acquire maternal antibody. Horses lack transplacental antibody transfer. Next, a randomized, controlled, blinded challenge was conducted by inoculating at ~4 weeks of age ~10⁶ cfu of R. equi via intrabronchial challenge. Eleven of 12 (91%) foals born to immune mares did not develop clinical R. equi pneumonia, whereas 6 of 7 (86%) foals born to unvaccinated controls developed pneumonia (P = 0.0017). In a confirmatory passive immunization study, infusion of PNAG-hyperimmune plasma protected 100% of 5 foals against R. equi pneumonia whereas all 4 recipients of normal horse plasma developed clinical disease (P = 0.0079). Antibodies to PNAG mediated killing of extracellular and intracellular R. equi and other intracellular pathogens. Killing of intracellular organisms depended on antibody recognition of surface expression of PNAG on infected cells, along with complement deposition and PMN-assisted lysis of infected macrophages. Peripheral blood mononuclear cells from immune and protected foals released higher levels of interferon-γ in response to PNAG compared to controls, indicating vaccination also induced an antibody-dependent cellular release of this critical immune cytokine. Overall, antibody-mediated opsonic killing and interferon-γ release in response to PNAG may protect against diseases caused by intracellular bacterial pathogens.

Development of effective vaccines for diseases such as tuberculosis, brucellosis and others caused by intracellular pathogens has proved challenging, as data exist supporting both antibody and cellular immune effectors as mediators of protection. To address this problem against an important, and representative, equine intracellular pathogen, we chose to test a vaccine candidate for the ability to protect horse foals challenged at 4 weeks of age with Rhodococcus equi. To make these foals immune, their pregnant mares were immunized with a vaccine targeting the conserved surface antigen found on many microbes, termed PNAG. Antibody in the pregnant mares was transferred to their foals and, after the foals were challenged, 91% of those born to vaccinated mares were protected against R. equi pneumonia. Meanwhile, 86% of the non-vaccinated controls developed pneumonia. We also showed antibody to PNAG could kill various bacteria that produce this antigen when residing inside of human macrophage cells, a new mechanism for antibody-mediated immunity to intracellular bacteria. These results support the development of PNAG as a vaccine for intracellular bacterial pathogens.

Salt-Induced Stress Stimulates a Lipoteichoic Acid-Specific Three-Component Glycosylation System in Staphylococcus aureus

Lipoteichoic acid (LTA) in Staphylococcus aureus is a poly-glycerophosphate polymer anchored to the outer surface of the cell membrane. LTA has numerous roles in cell envelope physiology, including regulating cell autolysis, coordinating cell division, and adapting to environmental growth conditions. LTA is often further modified with substituents, including d-alanine and glycosyl groups, to alter cellular function. While the genetic determinants of d-alanylation have been largely defined, the route of LTA glycosylation and its role in cell envelope physiology have remained unknown, in part due to the low levels of basal LTA glycosylation in S. aureus We demonstrate here that S. aureus utilizes a membrane-associated three-component glycosylation system composed of an undecaprenol (Und) N-acetylglucosamine (GlcNAc) charging enzyme (CsbB; SAOUHSC_00713), a putative flippase to transport loaded substrate to the outside surface of the cell (GtcA; SAOUHSC_02722), and finally an LTA-specific glycosyltransferase that adds α-GlcNAc moieties to LTA (YfhO; SAOUHSC_01213). We demonstrate that this system is specific for LTA with no cross recognition of the structurally similar polyribitol phosphate containing wall teichoic acids. We show that while wild-type S. aureus LTA has only a trace of GlcNAcylated LTA under normal growth conditions, amounts are raised upon either overexpressing CsbB, reducing endogenous d-alanylation activity, expressing the cell envelope stress responsive alternative sigma factor SigB, or by exposure to environmental stress-inducing culture conditions, including growth media containing high levels of sodium chloride.IMPORTANCE The role of glycosylation in the structure and function of Staphylococcus aureus lipoteichoic acid (LTA) is largely unknown. By defining key components of the LTA three-component glycosylation pathway and uncovering stress-induced regulation by the alternative sigma factor SigB, the role of N-acetylglucosamine tailoring during adaptation to environmental stresses can now be elucidated. As the dlt and glycosylation pathways compete for the same sites on LTA and induction of glycosylation results in decreased d-alanylation, the interplay between the two modification systems holds implications for resistance to antibiotics and antimicrobial peptides.

Advances in in Vitro and in Vivo Models for Studying the Staphylococcal Factors Involved in Implant Infections

Implant infections due to staphylococci are one of the greatest threats facing patients receiving implant devices. For many years researchers have sought to understand the mechanisms involved in the adherence of the bacterium to the implanted device and the formation of the unique structure, the biofilm, which protects the indwelling bacteria from the host defence and renders them resistant to antibiotic treatment. A major goal has been to develop in vitro and in vivo models that adequately reflect the real-life situation. From the simple microtiter plate assay and scanning electron microscopy, tools for studying adherence and biofilm formation have since evolved to include specialised equipment for studying adherence, flow cell systems, real-time analysis of biofilm formation using reporter gene assays both in vitro and in vivo, and a wide variety of animal models. In this article, we discuss advances in the last few years in selected in vitro and in vivo models as well as future developments in the study of adherence and biofilm formation by the staphylococci.

Staphylococcus Biofilm Components as Targets for Vaccines and Drugs

Staphylococci have become the most common cause of nosocomial infections, especially in patients with predisposing factors such as indwelling or implanted foreign polymer bodies. The pathogenesis of foreign-body associated infections with S. aureus and S. epidermidis is mainly related to the ability of these bacteria to form thick, adherent multilayered biofilms. In a biofilm, staphylococci are protected against antibiotic treatment and attack from the immune system, thus making eradication of the infections problematic. This necessitates the discovery of novel prophylactic and therapeutic strategies to treat these infections. In this review, we provide an overview of staphylococcal biofilm components and discuss new possible approaches to controlling these persistent biofilm-dwelling bacteria.

Protection against Staphylococcus aureus and tetanus infections by a combined vaccine containing SasA and TeNT‑Hc in mice

In developing countries, trauma patients and neonates are vulnerable to Staphylococcus aureus (S. aureus) and Clostridium tetani infections. It has been suggested that a combined vaccine against the two infections may be a reliable and cost‑effective strategy. Previous studies have indicated that the S. aureus surface protein A (SasA) and the C fragment of tetanus neurotoxin (TeNT‑Hc) may be suitable candidates for a vaccine against S. aureus and tetanus infections, respectively. In the present study, mice were immunized with a combined vaccine containing SasA and TeNT‑Hc, which induced a robust immune response to both antigens, and mutual interference between SasA and TeNT‑Hc was not observed. In the S.aureus challenge model, the combined vaccine fully protected BALB/c mice against lethal intraperitoneal challenges with 3x109 colony‑forming units of a methicillin‑resistant S. aureus USA300 strain. In the TeNT challenge model, the combined vaccine conferred complete protection against a lethal dose of (2x103) xLD50 tetanus toxin. These results implied that SasA and TeNT‑Hc promising components for a combined vaccine against S. aureus and tetanus infections.

Immunological Outcomes of Antibody Binding to Glycans Shared between Microorganisms and Mammals

Glycans constitute basic cellular components of living organisms across biological kingdoms, and glycan-binding Abs participate in many cellular interactions during immune defense against pathogenic organisms. Glycan epitopes are expressed as carbohydrate-only entities or as oligomers or polymers on proteins and lipids. Such epitopes on glycoproteins may be formed by posttranslational modifications or neoepitopes resulting from metabolic-catabolic processes and can be altered during inflammation. Pathogenic organisms can display host-like glycans to evade the host immune response. However, Abs to glycans, shared between microorganisms and the host, exist naturally. These Abs are able to not only protect against infectious disease, but also are involved in host housekeeping functions and can suppress allergic disease. Despite the reactivity of these Abs to glycans shared between microorganisms and host, diverse tolerance-inducing mechanisms permit the B cell precursors of these Ab-secreting cells to exist within the normal B cell repertoire.

Global antibody response to Staphylococcus aureus live-cell vaccination

The pathogen Staphylococcus aureus causes a broad range of severe diseases and is feared for its ability to rapidly develop resistance to antibiotic substances. The increasing number of highly resistant S. aureus infections has accelerated the search for alternative treatment options to close the widening gap in anti-S. aureus therapy. This study analyses the humoral immune response to vaccination of Balb/c mice with sublethal doses of live S. aureus. The elicited antibody pattern in the sera of intravenously and intramuscularly vaccinated mice was determined using of a recently developed protein array. We observed a specific antibody response against a broad set of S. aureus antigens which was stronger following i.v. than i.m. vaccination. Intravenous but not intramuscular vaccination protected mice against an intramuscular challenge infection with a high bacterial dose. Vaccine protection was correlated with the strength of the anti-S. aureus antibody response. This study identified novel vaccine candidates by using protein microarrays as an effective tool and showed that successful vaccination against S. aureus relies on the optimal route of administration.

Intramammary Immunization of Pregnant Mice with Staphylococcal Protein A Reduces the Post-Challenge Mammary Gland Bacterial Load but Not Pathology

Protein A, encoded by the spa gene, is one of the major immune evading MSCRAMM of S. aureus, demonstrated to be prevalent in a significant percentage of clinical bovine mastitis isolates in Australia. Given its’ reported significance in biofilm formation and the superior performance of S. aureus biofilm versus planktonic vaccine in the mouse mastitis model, it was of interest to determine the immunogenicity and protective potential of Protein A as a potential vaccine candidate against bovine mastitis using the mouse mastitis model. Pregnant Balb/c mice were immunised with Protein A emulsified in an alum-based adjuvant by subcutaneous (s/c) or intramammary (i/mam) routes. While humoral immune response of mice post-immunization were determined using indirect ELISA, cell-mediated immune response was assessed by estimation of interferon-gamma (IFN-γ) produced by protein A-stimulated splenocyte supernatants. Protective potential of Protein A against experimental mastitis was determined by challenge of immunized versus sham-vaccinated mice by i/mam route, based upon manifestation of clinical symptoms, total bacterial load and histopathological damage to mammary glands. Significantly (p<0.05) higher levels of IgG1 isotype were produced in mice immunized by the s/c route. In contrast, significantly higher levels of the antibody isotype IgG2a were produced in mice immunized by the i/mam route (p<0.05). There was significant reduction (p<0.05) in bacterial loads of the mammary glands of mice immunized by Protein A regardless of the route of immunization, with medium level of clinical symptoms observed up to day 3 post-challenge. However, Protein A vaccine failed to protect immunized mice post-challenge with biofilm producing encapsulated S. aureus via i/mam route, regardless of the route of immunization, as measured by the level of mammary tissue damage. It was concluded that, Protein A in its’ native state was apparently not a suitable candidate for inclusion in a cell-free vaccine formulation against mastitis.

Enzymatic modifications of exopolysaccharides enhance bacterial persistence

Biofilms are surface-attached communities of bacterial cells embedded in a self-produced matrix that are found ubiquitously in nature. The biofilm matrix is composed of various extracellular polymeric substances, which confer advantages to the encapsulated bacteria by protecting them from eradication. The matrix composition varies between species and is dependent on the environmental niche that the bacteria inhabit. Exopolysaccharides (EPS) play a variety of important roles in biofilm formation in numerous bacterial species. The ability of bacteria to thrive in a broad range of environmental settings is reflected in part by the structural diversity of the EPS produced both within individual bacterial strains as well as by different species. This variability is achieved through polymerization of distinct sugar moieties into homo- or hetero-polymers, as well as post-polymerization modification of the polysaccharide. Specific enzymes that are unique to the production of each polymer can transfer or remove non-carbohydrate moieties, or in other cases, epimerize the sugar units. These modifications alter the physicochemical properties of the polymer, which in turn can affect bacterial pathogenicity, virulence, and environmental adaptability. Herein, we review the diversity of modifications that the EPS alginate, the Pel polysaccharide, Vibrio polysaccharide, cepacian, glycosaminoglycans, and poly-N-acetyl-glucosamine undergo during biosynthesis. These are EPS produced by human pathogenic bacteria for which studies have begun to unravel the effect modifications have on their physicochemical and biological properties. The biological advantages these polymer modifications confer to the bacteria that produce them will be discussed. The expanding list of identified modifications will allow future efforts to focus on linking these modifications to specific biosynthetic genes and biofilm phenotypes.

Comparative studies of the immunogenicity and protective potential of biofilm vs planktonic Staphylococcus aureus vaccine against bovine mastitis using non-invasive mouse mastitis as a model system

This study was undertaken to compare the immunogenicity and protective potential of biofilm vs planktonic Staphylococcus aureus vaccine for the prevention of mastitis using the mouse as a model system. Mice immunized with formalin-killed whole cell vaccine of S. aureus residing in a biofilm when delivered via an intramammary route produced a cell mediated immune response. Mice immunized with this biofilm vaccine showed significant reductions in colonization by S. aureus in mammary glands, severity of clinical symptoms and tissue damage in mammary glands in comparison with the mice immunized with formalin-killed whole cells of planktonic S. aureus. The planktonic vaccine administered by a subcutaneous route produced a significantly higher humoral immune response (IgG1 and IgG) than the biofilm vaccine. However, considering the host response, tissue damage, the clinical severity and colonization of S. aureus in mammary glands, the biofilm vaccine performed better in immunogenicity and protective potential when administered by the intramammary route.

Mini-review: Staphylococcus epidermidis as the most frequent cause of nosocomial infections: old and new fighting strategies

Staphylococcus epidermidis is nowadays regarded as the most frequent cause of nosocomial infections and indwelling medical device-associated infections. One of the features that contributes to the success of this microorganism and which is elemental to the onset of pathogenesis is its ability to form biofilms. Cells in this mode of growth are inherently more resistant to antimicrobials. Seeking to treat staphylococcal-related infections and to prevent their side effects, such as the significant morbidity and health care costs, many efforts are being made to develop of new and effective antistaphylococcal drugs. Indeed, due to its frequency and extreme resistance to treatment, staphylococcal-associated infections represent a serious burden for the public health system. This review will provide an overview of some conventional and emerging anti-biofilm approaches in the management of medical device-associated infections related to this important nosocomial pathogen.

Biomolecular mechanisms of staphylococcal biofilm formation

The multitude of biomolecular and regulatory factors involved in staphylococcal adhesion and biofilm formation owe much to their ability to colonize surfaces, allowing the biofilm form to become the preferential bacterial phenotype. Judging by total number, biomass and variety of environments colonized, bacteria can be categorized as the most successful lifeform on earth. This is due to the ability of bacteria and other microorganisms to respond phenotypically via biomolecular processes to the stresses of their surrounding environment. This review focuses on the specific pathways involved in the adhesion of the Gram-positive bacteria Staphylococcus epidermidis and Staphylococcus aureus with reference to the role of specific cell surface adhesins, the ica operon, accumulation-associated proteins and quorum-sensing systems and their significance in medical device-related infection.

Molecular basis of in vivo biofilm formation by bacterial pathogens

Bacterial biofilms are involved in a multitude of serious chronic infections. In recent years, modeling of biofilm infection in vitro has led to the identification of microbial determinants that govern biofilm development. However, we lack information as to whether the biofilm formation mechanisms identified in vitro have relevance for biofilm-associated infection. Here, we discuss the molecular basis of biofilm formation. Staphylococci and Pseudomonas aeruginosa are used to illustrate key points because their biofilm development process has been well studied. We focus on in vivo findings, such as obtained in animal infection models, and critically evaluate the in vivo relevance of in vitro findings. Although conflicting results about the role of quorum sensing in biofilm formation have been obtained, we argue that integration of in vitro and in vivo studies allows a differentiated view of this mechanism as it relates to biofilm infection.

Noninvasive Staphylococcus aureus biofilm determination in chronic rhinosinusitis by detecting the exopolysaccharide matrix component poly-N-acetylglucosamine

BACKGROUND

The role that bacterial biofilms might play in recalcitrant forms of chronic rhinosinusitis (CRS) is increasingly being recognized. However, the detection of bacteria existing in this form, using standard culture, is limited by their unique metabolically inactive properties. All current biofilm diagnostic modalities require invasive mucosal biopsies, which limit their use to the operating theatre.

METHODS

Twenty CRS patients and 5 controls were enrolled in a prospective study to assess the feasibility of noninvasively diagnosing S. aureus biofilms by detecting the biofilm matrix polysaccharide poly-N-acetylglucosamine (PNAG). An immunofluorescence protocol was developed for PNAG detection and compared with both standard microbiological cultures and fluorescence in situ hybridization (FISH).

RESULTS

Thirteen of 20 CRS patients had evidence of S. aureus biofilm formation using FISH. Of these, 12 had detectable PNAG. Interestingly none of the S. aureus FISH-negative patients were PNAG-positive despite the presence of coagulase-negative Staphylococci biofilms, some of which may exhibit PNAG in their pathogenic forms. The development of a noninvasive S. aureus biofilm diagnostic test provides a reliable means to identify a high-risk group of CRS patients who harbor S. aureus biofilms. The ability to be used outside of the perioperative period to assess surgical efficacy, guide management, and evaluate new treatment modalities provides a significant advance in this field of research and clinical practice.

CONCLUSION

This study has confirmed the feasibility of noninvasive detection of S. aureus biofilms with a simple test that produces results comparable to the more invasive methods that are currently relied upon.

Immunity induced by Staphylococcus aureus surface protein A was protective against lethal challenge of Staphylococcus aureus in BALB/c mice

Staphylococcus aureus is the most common cause of hospital-acquired bacteremia. Due to emergence of antibiotic-resistant strains, these infections present a serious public health threat. In this study, to develop a broadly protective vaccine, we tested whether immune responses induced by several proteins associated with S. aureus toxicity could protect mice from lethal challenge with human clinical S. aureus isolate USA300. We found that the surface protein A (SasA) of S. aureus could protect mice from lethal challenge of the bacteria.

Vaccination with SesC decreases Staphylococcus epidermidis biofilm formation

The increased use of medical implants has resulted in a concomitant rise in device-related infections. The majority of these infections are caused by Staphylococcus epidermidis biofilms. Immunoprophylaxis and immunotherapy targeting in vivo-expressed, biofilm-associated, bacterial cell surface-exposed proteins are promising new approaches to prevent and treat biofilm-related infections, respectively. Using an in silico procedure, we identified 64 proteins that are predicted to be S. epidermidis surface exposed (Ses), of which 36 were annotated as (conserved) hypothetical. Of these 36 proteins, 5 proteins-3 LPXTG motif-containing proteins (SesL, SesB, and SesC) and 2 of the largest ABC transporters (SesK and SesM)-were selected for evaluation as vaccine candidates. This choice was based on protein size, number of antigenic determinants, or the established role in S. epidermidis biofilm formation of the protein family to which the candidate protein belongs. Anti-SesC antibodies exhibited the greatest inhibitory effect on S. epidermidis biofilm formation in vitro and on colonization and infection in a mouse jugular vein catheter infection model that includes biofilms and organ infections. Active vaccination with a recombinant truncated SesC inhibited S. epidermidis biofilm formation in a rat model of subcutaneous foreign body infection. Antibodies to SesC were shown to be opsonic by an in vitro opsonophagocytosis assay. We conclude that SesC is a promising target for antibody mediated strategies against S. epidermidis biofilm formation.

An extracellular Staphylococcus epidermidis polysaccharide: relation to Polysaccharide Intercellular Adhesin and its implication in phagocytosis

BACKGROUND

The skin commensal and opportunistic pathogen Staphylococcus epidermidis is a leading cause of hospital-acquired and biomaterial-associated infections. The polysaccharide intercellular adhesin (PIA), a homoglycan composed of β-1,6-linked N-acetylglucosamine residues, synthesized by enzymes encoded in icaADBC is a major functional factor in biofilm accumulation, promoting virulence in experimental biomaterial-associated S. epidermidis infection. Extracellular mucous layer extracts of S. epidermidis contain another major polysaccharide, referred to as 20-kDa polysaccharide (20-kDaPS), composed mainly out of glucose, N-acetylglucosamine, and being partially sulfated. 20-kDaPS antiserum prevents adhesion of S. epidermidis on endothelial cells and development of experimental keratitis in rabbits. Here we provide experimental evidence that 20-kDaPS and PIA represent distinct molecules and that 20-kDaPS is implicated in endocytosis of S. epidermidis bacterial cells by human monocyte-derived macrophages.

RESULTS

Analysis of 75 clinical coagulase-negative staphylococci from blood-cultures and central venous catheter tips indicated that 20-kDaPS is expressed exclusively in S. epidermidis but not in other coagulase-negative staphylococcal species. Tn917-insertion in various locations in icaADBC in mutants M10, M22, M23, and M24 of S. epidermidis 1457 are abolished for PIA synthesis, while 20-kDaPS expression appears unaltered as compared to wild-type strains using specific anti-PIA and anti-20-kDaPS antisera. While periodate oxidation and dispersin B treatments abolish immuno-reactivity and intercellular adhesive properties of PIA, no abrogative activity is exerted towards 20-kDaPS immunochemical reactivity following these treatments. PIA polysaccharide I-containing fractions eluting from Q-Sepharose were devoid of detectable 20-kDaPS using specific ELISA. Preincubation of non-20-kDaPS-producing clinical strain with increasing amounts of 20-kDaPS inhibits endocytosis by human macrophages, whereas, preincubation of 20-kDaPS-producing strain ATCC35983 with 20-kDaPS antiserum enhances bacterial endocytosis by human macrophages.

CONCLUSIONS

In conclusion, icaADBC is not involved in 20-kDaPS synthesis, while the chemical and chromatographic properties of PIA and 20-kDaPS are distinct. 20-kDaPS exhibits anti-phagocytic properties, whereas, 20-kDaPS antiserum may have a beneficial effect on combating infection by 20-kDaPS-producing S. epidermidis.

Recurrent infections and immune evasion strategies of Staphylococcus aureus

Staphylococcus aureus causes purulent skin and soft tissue infections (SSTIs) that frequently reoccur. Staphylococal SSTIs can lead to invasive disease and sepsis, which are among the most significant causes of infectious disease mortality in both developed and developing countries. Human or animal infections with S. aureus do not elicit protective immunity against staphylococcal diseases. Here we review what is known about the immune evasive strategies of S. aureus that enable the pathogen's escape from protective immune responses. Three secreted products are discussed in detail, staphylococcal protein A (SpA), staphylococcal binder of immunoglobulin (Sbi) and adenosine synthase A (AdsA). By forming a complex with V(H)3-type IgM on the surface of B cells, SpA functions as a superantigen to modulate antibody responses to staphylococcal infection. SpA also captures pathogen-specific antibodies by binding their Fcγ portion. The latter activity of SpA is shared by Sbi, which also associates with complement factors 3d and factor H to promote the depletion of complement. AdsA synthesizes the immune signaling molecule adenosine, thereby dampening innate and adaptive immune responses during infection. We discuss strategies how the three secreted products of staphylococci may be exploited for the development of vaccines and therapeutics.

Exopolysaccharide Production by Staphylococcus Epidermidis and its Relationship with Biofilm Extracellular DNA

Implant-related infections are difficult to treat because they are very often associated with biofilm-forming micro-organisms capable of resisting host immune defenses and surviving conventional antibiotic treatments. In Staphylococcus epidermidis biofilm-forming strains, the polysaccharide intercellular adhesin (PIA), whose expression is encoded by the icaADBC operon, is recognized as a main staphylococcal accumulation mechanism. Nevertheless, various observations have shown that PIA expression is dispensable and a variety of additional/alternative accumulation mechanisms, including extracellular DNA (eDNA) and several other factors of proteic nature, can compensate for icaADBC low expression or even for its absence. A suggestive hypothesis points to the possibility that changes in biofilm extracellular matrix composition can be induced in different environmental niches. In this study we aimed at investigating the relationship between the exopolysaccharide and eDNA biofilm components, screening 55 S. epidermidis clinical isolates by means of a simple fluorescence-based microtiter-plate assay. Our findings indicate the existence of a certain degree of correlation, although not a strict one, between eDNA and the exopolysaccharide component. The presence of exopolysaccharide greatly varied even in strains belonging to the same strain type determined by automated riboprinting.

Animal and human antibodies to distinct Staphylococcus aureus antigens mutually neutralize opsonic killing and protection in mice

New prophylactic approaches are needed to control infection with the Gram-positive bacterium Staphylococcus aureus, which is a major cause of nosocomial and community-acquired infections. To develop these, greater understanding of protective immunity against S. aureus infection is needed. Human immunity to extracellular Gram-positive bacterial pathogens is primarily mediated by opsonic killing (OPK) via antibodies specific for surface polysaccharides. S. aureus expresses two such antigens, capsular polysaccharide (CP) and poly-N-acetyl glucosamine (PNAG). Here, we have shown that immunization-induced polyclonal animal antisera and monoclonal antibodies specific for either CP or PNAG antigens have excellent in vitro OPK activity in human blood but that when mixed together they show potent interference in OPK activity. In addition, reductions in antibody binding to the bacterial surface, complement deposition, and passive protection were seen in two mouse models of S. aureus infection. Electron microscopy, isothermal calorimetry, and surface plasmon resonance indicated that antibodies to CP and PNAG bound together via an apparent idiotype-anti-idiotype interaction. This interaction was also found in sera from humans with S. aureus bacteremia. These findings suggest that the lack of effective immunity to S. aureus infections in humans could be due, in part, to interference in OPK when antibodies to CP and PNAG antigens are both present. This information could be used to better design S. aureus vaccine components.

Why antibodies disobey the Hippocratic Oath and end up doing harm: a new clue

The appearance of methicillin-resistant Staphylococcus aureus (MRSA) as an endemic microbe, first in hospital and health care settings and more recently in the community, has led to a disastrous situation in which use of the available antibiotic armamentarium is increasingly ineffective and spawns further antibiotic resistance. This vicious cycle highlights the pressing need for an S. aureus vaccine. However, to date, clinical trials with S. aureus vaccines have not demonstrated sustained efficacy. In this issue of the JCI, Skurnik and colleagues report that specific antibodies to two different S. aureus surface polysaccharides, which independently promote effector cell killing of S. aureus in vitro and protection against S. aureus in animal models, bind to and abrogate the activity of one another when they are combined. This fascinating finding suggests a new paradigm to explain the failure of antibody immunity to S. aureus.

A comparative analysis of phenotypic and genotypic methods for the determination of the biofilm-forming abilities of Staphylococcus epidermidis

The collection of 146 Staphylococcus epidermidis strains isolated from the nasopharynx of lung cancer patients has been studied for the ability of slime secretion and biofilm formation using the Congo red agar (CRA) test and the microtiter plate (MtP) method, respectively. The prevalence of the icaAD and the aap genes was also analyzed. Some isolates (35.6%) were biofilm positive by the MtP method, while 58.9% of isolates exhibited a slime-positive phenotype by the CRA test. The sensitivities of the CRA test evaluated using the MtP method as a gold standard of biofilm production were 73.1%, 97.3% and 13.3% for all the strains screened, ica-positive and ica-negative strains, respectively. The genotype ica(+)aap(+) was correlated with a strong biofilm-producer phenotype. Interestingly, some of the ica(-)aap(-) isolates could also form a biofilm. The correlation between the presence of icaAD genes and the biofilm-positive phenotype by the MtP method as well as slime production by the CRA test was statistically significant (P<0.0001). However, some S. epidermidis strains possess the potential ability of ica-independent biofilm formation; thus, further studies are needed to determine reliable, short-time criteria for an in vitro assessment of biofilm production by staphylococci.

Study of the humoral immunological response after vaccination with a Staphylococcus aureus biofilm-embedded bacterin in dairy cows: possible role of the exopolysaccharide specific antibody production in the protection from Staphylococcus aureus induced mastitis

The objective of the present study was to analyze an extracellular component from Staphylococcus aureus (S. aureus), which we refer to as slime associated antigenic complex (SAAC), and to investigate the role of SAAC-specific antibody production in protection from S. aureus bovine mastitis. Twelve primiparous gestating cows were randomly assigned to one of the three groups: Group 1 was vaccinated with a S. aureus bacterin with very limited SAAC content; Group 2 received a S. aureus bacterin with high SAAC content and Group 3 served as unvaccinated controls. Animals were vaccinated at 45 days before the expected parturition date and revaccinated 35 days later. All groups were challenged by intramammary infusion with a virulent heterologous strain of S. aureus 23 days after calving. Antibody response against SAAC in serum and in milk, general clinical signs, mastitis score, somatic cell count (SCC) and count of S. aureus in milk were evaluated before and after challenge. Immunization with a high SAAC content in the S. aureus bacterin (Group 2) significantly enhanced antibody titers against SAAC (in serum and milk) and reduced the S. aureus concentration in milk during the post-challenge period compared to Group 1 and Group 3. Moreover, a significant negative correlation was observed between SAAC antibody production on the day of the challenge and the S. aureus count in milk by 1 day after challenge. However, there was no evidence of a difference between vaccinated and control groups with regard to clinical signs of mastitis following the challenge. Nevertheless, the SAAC antibody concentration on the day of the challenge negatively correlated with the mastitis score in quarters infected with S. aureus at 2 days post-challenge. These results indicate that the vaccines did not prevent S. aureus intramammary infection (IMI) after the experimental challenge, but immunization with a S. aureus bacterin with high SAAC content was able to reduce S. aureus multiplication in the mammary gland after challenge and suggests that the SAAC-specific antibody response could be involved in the protection against S. aureus intramammary infection. Although further studies should be performed to confirm the efficacy (under experimental conditions and in field trials), we propose bacterins from strong biofilm-producing bacteria and with high SAAC content, rather than with limited SAAC content, as a cost-efficient vaccine design against S. aureus bovine mastitis.

The pgaABCD locus of Acinetobacter baumannii encodes the production of poly-beta-1-6-N-acetylglucosamine, which is critical for biofilm formation

We found that Acinetobacter baumannii contains a pgaABCD locus that encodes proteins that synthesize cell-associated poly-beta-(1-6)-N-acetylglucosamine (PNAG). Both a mutant with an in-frame deletion of the pga locus (S1Deltapga) and a transcomplemented strain (S1Deltapga-c) of A. baumannii were constructed, and the PNAG production by these strains was compared using an immunoblot assay. Deleting the pga locus resulted in an A. baumannii strain without PNAG, and transcomplementation of the S1Deltapga strain with the pgaABCD genes fully restored the wild-type PNAG phenotype. Heterologous expression of the A. baumannii pga locus in Escherichia coli led to synthesis of significant amounts of PNAG, while no polysaccharide was detected in E. coli cells harboring an empty vector. Nuclear magnetic resonance analysis of the extracellular polysaccharide material isolated from A. baumannii confirmed that it was PNAG, but notably only 60% of the glucosamine amino groups were acetylated. PCR analysis indicated that all 30 clinical A. baumannii isolates examined had the pga genes, and immunoblot assays indicated that 14 of the 30 strains strongly produced PNAG, 14 of the strains moderately to weakly produced PNAG, and 2 strains appeared to not produce PNAG. Deletion of the pga locus led to loss of the strong biofilm phenotype, which was restored by complementation. Confocal laser scanning microscopy studies combined with COMSTAT analysis demonstrated that the biovolume, mean thickness, and maximum thickness of 16-h and 48-h-old biofilms formed by wild-type and pga-complemented A. baumannii strains were significantly greater than the biovolume, mean thickness, and maximum thickness of 16-h and 48-h-old biofilms formed by the S1Deltapga mutant strain. Biofilm-dependent production of PNAG could be an important virulence factor for this emerging pathogen that has few known virulence factors.

Protection from Staphylococcus aureus mastitis associated with poly-N-acetyl beta-1,6 glucosamine specific antibody production using biofilm-embedded bacteria

Staphylococcus aureus vaccines based on bacterins surrounded by slime, surface polysaccharides coupled to protein carriers and polysaccharides embedded in liposomes administered together with non-biofilm bacterins confer protection against mastitis. However, it remains unknown whether protective antibodies are directed to slime-associated known exopolysaccharides and could be produced in the absence of bacterin immunizations. Here, a sheep mastitis vaccination study was carried out using bacterins, crude bacterial extracts or a purified exopolysaccharide from biofilm bacteria delivered in different vehicles. This polysaccharide reacted specifically with antibodies to poly-N-acetyl-beta-1,6-glucosamine (PNAG) and not with antibodies to other capsular antigens or bacterial components. Following intra-mammary challenge with biofilm-producing bacteria, antibody production against the polysaccharide, milk bacterial counts and mastitis lesions were determined. Bacterins from strong biofilm-producing bacteria triggered the highest production of antibodies to PNAG and conferred the highest protection against infection and mastitis, compared with weak biofilm-producing bacteria and non-cellular inocula. Thus, bacterins from strong biofilm bacteria, rather than purified polysaccharide, are proposed as a cost-efficient vaccination against S. aureus ruminant mastitis.

IFN-gamma regulated chemokine production determines the outcome of Staphylococcus aureus infection

Immunomodulatory therapy represents an attractive approach in treating multidrug-resistant infections. Developing this therapy necessitates a lucid understanding of host defense mechanisms. Neutrophils represent the first line of systemic defense during Staphylococcus aureus infections. However, recent research suggests that survival of S. aureus inside neutrophils may actually contribute to pathogenesis, indicating that neutrophil trafficking to the infection site must be tightly regulated to ensure efficient microbial clearance. We demonstrate that neutrophil-regulating T cells are activated during S. aureus infection and produce cytokines that control the local neutrophil response. S. aureus capsular polysaccharide activates T cell production of IFN-gamma in a novel MHC class II-dependent mechanism. During S. aureus surgical wound infection, the presence of IFN-gamma at the infection site depends upon alphabetaTCR+ cells and functions to regulate CXC chemokine production and neutrophil recruitment in vivo. We note that the reduced neutrophil response seen in IFN-gamma-/- mice during S. aureus infection is associated with reduced tissue bacterial burden. CXC chemokine administration to the infection site resulted in an increased survival of viable S. aureus inside neutrophils isolated from the wound. These data demonstrate that T cell-derived IFN-gamma generates a neutrophil-rich environment that can potentiate S. aureus pathogenesis by facilitating bacterial survival within the neutrophil. These findings suggest avenues for novel immunomodulatory approaches to control S. aureus infections.

Potential use of poly-N-acetyl-beta-(1,6)-glucosamine as an antigen for diagnosis of staphylococcal orthopedic-prosthesis-related infections

Staphylococcus aureus and coagulase-negative staphylococci are microorganisms most frequently isolated from orthopedic-implant-associated infections. Their capacity to maintain these infections is thought to be related to their ability to form adherent biofilms. Poly-N-acetyl-beta-(1,6)-glucosamine (PNAG) is an important constituent of the extracellular biofilm matrix of staphylococci. In the present study, we explored the possibility of using PNAG as an antigen for detecting antibodies in the blood sera of patients with staphylococcal orthopedic-prosthesis-associated infections. First, we tested the presence of anti-PNAG antibodies in an animal model, in the blood sera of guinea pigs that developed an implant-associated infection caused by biofilm-forming, PNAG-producing strains of Staphylococcus epidermidis. Animals infected with S. epidermidis RP62A showed levels of anti-PNAG immunoglobulin G (IgG) significantly higher than those of the control group. The comparative study of healthy individuals and patients with staphylococcal prosthesis-related infections showed that (i) relatively high levels of anti-PNAG IgG were present in the blood sera of the healthy control group, (ii) the corresponding levels in the infected patients were slightly but not significantly higher, and (iii) only 1 of 10 patients had a level of anti-PNAG IgM significantly higher than that of the control group. In conclusion, the encouraging results obtained in the animal study could not be readily applied for the diagnosis of staphylococcal orthopedic-prosthesis-related infections in humans, and PNAG does not seem to be an appropriate antigen for this purpose. Further studies are necessary to determine whether the developed enzyme-linked immunosorbent assay method could serve as a complementary test in the individual follow-up treatment of such infections caused by PNAG-producing staphylococci.

Staphylococcal biofilm exopolysaccharide protects against Caenorhabditis elegans immune defenses

Staphylococcus epidermidis and Staphylococcus aureus are leading causes of hospital-acquired infections that have become increasingly difficult to treat due to the prevalence of antibiotic resistance in these organisms. The ability of staphylococci to produce biofilm is an important virulence mechanism that allows bacteria both to adhere to living and artificial surfaces and to resist host immune factors and antibiotics. Here, we show that the icaADBC locus, which synthesizes the biofilm-associated polysaccharide intercellular adhesin (PIA) in staphylococci, is required for the formation of a lethal S. epidermidis infection in the intestine of the model nematode Caenorhabditis elegans. Susceptibility to S. epidermidis infection is influenced by mutation of the C. elegans PMK-1 p38 mitogen-activated protein (MAP) kinase or DAF-2 insulin-signaling pathways. Loss of PIA production abrogates nematocidal activity and leads to reduced bacterial accumulation in the C. elegans intestine, while overexpression of the icaADBC locus in S. aureus augments virulence towards nematodes. PIA-producing S. epidermidis has a significant survival advantage over ica-deficient S. epidermidis within the intestinal tract of wild-type C. elegans, but not in immunocompromised nematodes harboring a loss-of-function mutation in the p38 MAP kinase pathway gene sek-1. Moreover, sek-1 and pmk-1 mutants are equally sensitive to wild-type and icaADBC-deficient S. epidermidis. These results suggest that biofilm exopolysaccharide enhances virulence by playing an immunoprotective role during colonization of the C. elegans intestine. These studies demonstrate that C. elegans can serve as a simple animal model for studying host–pathogen interactions involving staphylococcal biofilm exopolysaccharide and suggest that the protective activity of biofilm matrix represents an ancient conserved function for resisting predation.

Biofilm is an agglomeration of microbes bound together by a slimy matrix composed of excreted proteins and polysaccharide polymers. Most bacteria in the environment reside in biofilms, as do 80% or more of those causing human infections, according to some estimates. During infection, biofilm matrix acts as a safe haven, protecting bacterial cells from antibiotics, immune cells, and antimicrobial factors. In this report, we demonstrate that the ability of Staphylococcus epidermidis to produce a lethal infection within the intestinal tract of the roundworm Caenorhabditis elegans depends on the S. epidermidis intercellular adhesion (ica) locus, which is responsible for the synthesis of the principal exopolysaccharide of staphylococcal biofilm, polysaccharide intercellular adhesin (PIA). Using a collection of bacterial and nematode mutants, we show that PIA promotes infection by working against protective immune factors controlled by the C. elegans SEK-1 PMK-1 p38 mitogen-activated protein kinase pathway. In addition to providing further evidence for the immunoprotective function of the biofilm polymer PIA, these results show that C. elegans can be used in a simple, live animal model for the study of host–pathogen interactions involving biofilm matrix.

Susceptibility of staphylococcal biofilms to enzymatic treatments depends on their chemical composition

Bacterial infections are serious complications after orthopaedic implant surgery. Staphylococci, with Staphylococcus epidermidis as a leading species, are the prevalent and most important species involved in orthopaedic implant-related infections. The biofilm mode of growth of these bacteria on an implant surface protects the organisms from the host's immune system and from antibiotic therapy. Therapeutic agents that disintegrate the biofilm matrix would release planktonic cells into the environment and therefore allow antibiotics to eliminate the bacteria. An addition of a biofilm-degrading agent to a solution used for washing-draining procedures of infected orthopaedic implants would greatly improve the efficiency of the procedure and thus help to avoid the removal of the implant. We have previously shown that the extracellular staphylococcal matrix consists of a poly-N-acetylglucosamine (PNAG), extracellular teichoic acids (TAs) and protein components. In this study, we accessed the sensitivity of pre-formed biofilms of five clinical staphylococcal strains associated with orthopaedic prosthesis infections and with known compositions of the biofilm matrix to periodate, Pectinex Ultra SP, proteinase K, trypsin, pancreatin and dispersin B, an enzyme with a PNAG-hydrolysing activity. We also tested the effect of these agents on the purified carbohydrate components of staphylococcal biofilms, PNAG and TA. We found that the enzymatic detachment of staphylococcal biofilms depends on the nature of their constituents and varies between the clinical isolates. We suggest that a treatment with dispersin B followed by a protease (proteinase K or trypsin) could be capable to eradicate biofilms of a variety of staphylococcal strains on inert surfaces.

Molecular basis for preferential protective efficacy of antibodies directed to the poorly acetylated form of staphylococcal poly-N-acetyl-beta-(1-6)-glucosamine

Poly-N-acetyl-glucosamine (PNAG) is a staphylococcal surface polysaccharide influencing biofilm formation that is also under investigation for its vaccine potential. Antibodies that bind to PNAG with either low (<15%) or high (>90%) levels of acetate are superior at opsonic and protective activity compared with antibodies that bind to PNAG with only high levels (>70%) of acetate. PNAG is synthesized by four proteins encoded within the intercellular adhesin (ica) locus icaADBC. In Staphylococcus epidermidis, icaB encodes a deacetylase needed for the surface retention of PNAG and optimal biofilm formation. In this study, we confirmed that icaB plays a similar role in Staphylococcus aureus and found that an icaB mutant of S. aureus expressed significantly less surface-associated PNAG, was highly susceptible to antibody-independent opsonic killing that could not be enhanced with antibody raised against deacetylated PNAG (dPNAG), and had reduced survival capacity in a murine model of bacteremia. In contrast, an icaB-overexpressing strain produced primarily surface-associated PNAG, was more susceptible to opsonophagocytosis with antibody to dPNAG, and had increased survival in a murine bacteremia model. The highly acetylated secreted PNAG was more effective at blocking opsonic killing mediated by a human monoclonal antibody (mAb) to native PNAG than it was at blocking killing mediated by a human mAb to dPNAG, which by itself was a more effective opsonin. Retention of dPNAG on the surface of S. aureus is key to increased survival during bacteremia and also provides a molecular mechanism explaining the superior opsonic and protective activity of antibody to dPNAG.

Protection against Escherichia coli infection by antibody to the Staphylococcus aureus poly-N-acetylglucosamine surface polysaccharide

Poly-N-acetylglucosamine (PNAG) is a surface polysaccharide produced by Staphylococcus aureus and Staphylococcus epidermidis and is an effective target for opsonic and protective Ab for these two organisms. Recently, it has been found that Escherichia coli produces an exo-polysaccharide, designated polyglucosamine, that is biochemically indistinguishable from PNAG. We analyzed 30 E. coli strains isolated from urinary tract and neonatal bloodstream infections for the pga locus, PNAG antigen production, and susceptibility to opsonic killing and protection from lethal infection by Ab to PNAG. Twenty-six of 30 strains carried the pga locus, 25 of 30 expressed immunologically detectable PNAG, and 21 of 30 could be killed by rabbit IgG specific for the deacetylated form of the staphylococcal PNAG. Ab to staphylococcal PNAG protected mice against lethality from five different E. coli strains expressing PNAG. PNAG expression by both Gram-negative and Gram-positive organisms could make this antigen a conserved vaccine target for multiple pathogenic species of bacteria.

Capillary Isoelectric Focusing — Useful tool for detection of the biofilm formation in Staphylococcus epidermidis

The biofilm formation is an important factor of S. epidermidis virulence. Biofilm-positive strains might be clinically more important than biofilm-negative ones. Unlike biofilm-negative staphylococci, biofilm-positive staphylococci are surrounded with an extracellular polysaccharide substance. The presence of this substance on the surface can affect physico-chemical properties of the bacterial cell, including surface charge. 73 S. epidermidis strains were examined for the presence of ica operon, for the ability to form biofilm by Christensen test tube method and for the production of slime by Congo red agar method. Isoelectric points (pI) of these strains were determined by means of Capillary Isoelectric Focusing. The biofilm negative strains focused near pI value 2.3, while the pI values of the biofilm positive strains were near 2.6. Isoelectric point is a useful criterion for the differentiation between biofilm-positive and biofilm-negative S. epidermidis strains.

Control and prevention of MRSA infections

Methicillin-resistant Staphylococcus aureus (MRSA) has posed an immense problem for clinicians in the hospital setting for years, emerging as the most frequent nosocomial infection. To deal with this problem pathogen and others, infectious disease specialists have developed a variety of procedures for their control and prevention, involving options from preventative measures such as decolonization and isolation of MRSA-confirmed patients, to the more simple procedures of hand washing, expanding glove use, and reducing time in the hospital. With the realization that MRSA is now a community problem, there are expanded efforts toward more direct intervention, such as the use of anti-MRSA antibacterials and vaccines, in an attempt to reduce the overall burden of MRSA.