Secretome,surfome and immunome: emerging approaches for the discovery of new vaccine candidates against bacterial infections

Functional genomics has made possible advanced structure-to-function investigation of pathogens and helped characterize virulence mechanisms. Proteomics has been become a tool for large-scale identification of proteins involved during invasion and infection by the pathogens. Bacterial surface and secreted proteins play key role in the interaction between the bacterial cell and the host environment. Thus exoproteome and surface proteome of a microorganism are hypothesized to contain components of effective vaccines. Surfome and exoproteome analysis strategy facilitates identification of novel vaccine antigen and overall helps in progress of discovery of vaccine. The study of the antibody response can advance how proteomics is used, because it investigates antibody–antigen interactions and also unravel the relationship of antibody responses to pathogen and host characteristics. System immunology integrating with proteome i.e. immunoproteomics is applicable to those infections that are having tendency of diverse antibody target recognition and thus accurately reflects progression of the infection.     

Antimicrobial peptides in oyster hemolymph: The bacterial connection

We have explored antimicrobial compounds in oyster hemolymph and purified four active peptides with molecular masses of 4464, 3158, 655 and 636 Da. While no exploitable structural elements were obtained for the former three, a partial amino acid sequence (X-P-P-X-X-I-V) was obtained for the latter, named Cg-636. Due to both its low MM and the presence of exotic amino acid residue (X), we suspected a bacterial origin and tracked cultivable hemolymph-resident bacteria of oyster for their antimicrobial abilities. Supernatants of 224 hemolymph resident bacteria coming from 60 oysters were screened against 10 target bacteria including aquaculture pathogens. Around 2% (5 strains) revealed antimicrobial activities. They belong to Pseudoalteromonas and Vibrio genera. Two closely related strains named hCg-6 and hCg-42 have been shown to produce Bacteriocin-Like Inhibitory Substances (BLIS) even in oyster hemolymph. We report herein first BLIS-producing bacteria isolated from bivalve hemolymph. These results strongly suggest that hemolymph resident bacteria may prevent pathogen establishment and pave the way for considering a role of resident bacteria into bivalve defense.     

Host defense peptides and the new line of defence against multiresistant infections

Increasing antibiotic resistance has led to an urgent need for new therapeutic approaches. Host defense peptides are known to be antimicrobial and have revealed broad immunomodulatory functions for both innate and adaptive immunity. This review will focus on the role of host defense peptides in infection and immune response and discuss its potential and limitations as a future therapeutical agent.     

Mini-review: Antimicrobial peptides and enzymes as promising candidates to functionalize biomaterial surfaces

Biomaterial-associated infections remain a serious concern in modern healthcare. The development of materials that can resist or prevent bacterial attachment constitutes a promising approach to dealing with this problem. Antimicrobial peptides (AMPs) and enzymes have been recognized as promising candidates for the new generation of antimicrobial surfaces. AMPs have been the focus of great interest in recent years owing to a low propensity for developing bacterial resistance, broad-spectrum activity, high efficacy at very low concentrations, target specificity, and synergistic action with classical antibiotics. Biofilm-dispersing enzymes have been shown to inhibit biofilm formation, detach established biofilm, and increase biofilm susceptibility to other antimicrobials. This review critically examines the potential of these protein-like compounds for developing antibacterial coatings by reporting their immobilization into different substrata using different immobilization strategies.     

Antimicrobial peptides protect coho salmon from Vibrio anguillarum infections

Fish losses from infectious diseases are a significant problem in aquaculture worldwide. Therefore, we investigated the ability of cationic antimicrobial peptides to protect against infection caused by the fish pathogen Vibrio anguillarum. To identify effective peptides for fish, the MICs of certain antimicrobial peptides against fish pathogens were determined in vitro. Two of the most effective antimicrobial peptides, CEME, a cecropin-melittin hybrid peptide, and pleurocidin amide, a C-terminally amidated form of the natural flounder peptide, were selected for in vivo studies. A single intraperitoneal injection of CEME did not affect mortality rates in juvenile coho salmon infected with V. anguillarum, the causative agent of vibriosis. Therefore, the peptides were delivered continuously using miniosmotic pumps placed in the peritoneal cavity. Twelve days after pump implantation, the fish received intraperitoneal injections of V. anguillarum at a dose that would kill 50 to 90% of the population. Fish receiving 200 microg of CEME per day survived longer and had significantly lower accumulated mortalities (13%) than the control groups (50 to 58%). Fish receiving pleurocidin amide at 250 microg per day also survived longer and had significantly lower accumulated mortalities (5%) than the control groups (67 to 75%). This clearly shows the potential for antimicrobial peptides to protect fish against infections and indicates that the strategy of overexpressing the peptides in transgenic fish may provide a method of decreasing bacterial disease problems.     

Recombinant lipoprotein-based vaccine candidates against C. difficile infections

Background

Opportunistically nosocomial infections in hospitalized patients are often related to Clostridium difficile infections (CDI) due to disruption of the intestinal micro-flora by antibiotic therapies during hospitalization. Clostridial exotoxins A and B (TcdA and TcdB) specifically bind to unknown glycoprotein(s) in the host intestine, disrupt the intestinal barrier leading to acute inflammation and diarrhea. The C-terminal receptor binding domain of TcdA (A-rRBD) has been shown to elicit antibody responses that neutralize TcdA toxicity in Vero cell cytotoxicity assays, but not effectively protect hamsters against a lethal dose challenge of C. difficile spores. To develop an effective recombinant subunit vaccine against CDI, A-rRBD was lipidated (rlipoA-RBD) as a rational design to contain an intrinsic adjuvant, a toll-like receptor 2 agonist and expressed in Escherichia coli.

Results

The purified rlipoA-RBD was characterized immunologically and found to have the following properties: (a) mice, hamsters and rabbits vaccinated with 3 μg of rlipoA-RBD produced strong antibody responses that neutralized TcdA toxicity in Vero cell cytotoxicity assays; furthermore, the neutralization titer was comparable to those obtained from antisera immunized either with 10 μg of TcdA toxoid or 30 μg of A-rRBD; (b) rlipoA-RBD elicited immune responses and protected mice from TcdA challenge, but offered insignificant protection (10 to 20 %) against C. difficile spores challenge in hamster models; (c) only rlipoA-RBD formulated with B-rRBD consistently confers protection (90 to 100 %) in the hamster challenge model; and (d) rlipoA-RBD was found to be 10-fold more potent than A-rRBD as an adjuvant to enhancing immune responses against a poor antigen such as ovalbumin.

Conclusion

These results indicate that rlipoA-RBD formulated with B-rRBD could be an excellent vaccine candidate for preclinical studies and future clinical trials.     

抗菌肽的抗生物膜机理研究进展

生物膜,也称为生物被膜,是指附着于有生命或无生命物体表面被细菌胞外大分子包裹的有组织的细菌群体。与浮游菌相比,生物膜内的细菌对抗生素的耐受性提高了10–1000倍,是造成目前细菌耐药的主要原因之一。作为一种新型抗菌制剂,抗菌肽的使用为生物膜感染的治疗提供了一种新的思路和手段。抗菌肽在抑制生物膜形成、杀灭生物膜内细菌以及消除成熟生物膜的过程中发挥了独特的优势。文中分析了近30年的数据,从细菌生物膜的结构入手,对抗菌肽可能的抗生物膜机理进行了综述,以期为抗菌肽临床治疗生物膜感染提供一定参考。     

The fight against new types of influenza virus

In 1997, during an outbreak in chickens in Hong Kong the avian H5N1 influenza virus crossed the species barrier and infected 18 people, of which 6 cases were fatal. The virus also infected wild birds and continued to circulate and mutate in geese and ducks in southeastern China. Since this occurrence, new antigenic variants that are highly pathogenic for humans as well as wild, domestic, and exotic waterfowl continue to appear in Hong Kong. This virus is spreading across Asia, and is encroaching upon Europe and other continents. Wild birds are now considered as the main reservoir of H5N1 virus. Humans become infected with this H5N1 virus usually via close contact with infected birds or a highly contaminated environment. The very low transmissibility of this virus prevented further person-to-person dissemination in spite of the complete absence of immunity in the human population to H5N1 viruses. Viruses of the H5N1 subtype are characterized by an exceptionally high pathogenicity for humans. The cause of the viral virulence is not known so far; however, several virulence factors are considered. The unprecedented capability of H5N1 viruses to kill humans intensifies the concern about its pandemic potential with catastrophic consequences. The effectiveness of existing antivirals as well as vaccines for humans and birds are reviewed.     

Patents on quorum quenching: interfering with bacterial communication as a strategy to fight infections

Numerous bacterial functions, such as virulence and biofilm formation, are controlled by a cell densitydependent communication mechanism known as Quorum Sensing (QS), in which small diffusible molecules are released, allowing bacteria to coordinate their behavior once a minimal effective quorum has been reached. The interference with these signaling systems, also known as Quorum Quenching (QQ), represents a promising strategy to tackle bacterial infections. The growing interest in this approach is reflected by the increasing number of patents within the field (45 up to now), especially in the last few years, as shown by patent applications published since 2009. The fact that biofilm formation is also controlled by QS systems expands the application of QQ to clinically-relevant biofilms such as those responsible for periodontal disease. Moreover, since biofilms increase bacterial resistance to antimicrobials, QQ could represent a new way to fight some of the most recurrent human pathogens, such as nosocomial multiresistant strains, and this deserves further exploration, especially through more proofs of concept. In this article we review the best known QS and QQ systems to date and we describe recent patents on the interference with this type of bacterial communication.     

Natural antimicrobial peptides from bacteria: characteristics and potential applications to fight against antibiotic resistance

Because of the emergence of antibiotic‐resistant pathogens worldwide, a number of infectious diseases have become difficult to treat. This threatening situation is worsened by the fact that very limited progress has been made in developing new and potent antibiotics in recent years. However, a group of antimicrobials, the so‐called bacteriocins, have been much studied lately because they hold a great potential in controlling antibiotic‐resistant pathogens. Bacteriocins are small antimicrobial peptides (AMPs) produced by numerous bacteria. They often act toward species related to the producer with a very high potency (at pico‐ to nanomolar concentration) and specificity. The common mechanisms of killing by bacteriocins are destruction of target cells by pore formation and/or inhibition of cell wall synthesis. Several studies have revealed that bacteriocins display great potential in the medical sector as bacteriocinogenic probiotics and in the clinic as therapeutic agents. In this review, we discuss the emerging antibiotic resistance and strategies to control its dissemination, before we highlight the potential of AMPs from bacteria as a new genre of antimicrobial agents.     

Metabolomics in the fight against malaria

Metabolomics uses high-resolution mass spectrometry to provide a chemical fingerprint of thousands of metabolites present in cells, tissues or body fluids. Such metabolic phenotyping has been successfully used to study various biologic processes and disease states. High-resolution metabolomics can shed new light on the intricacies of host-parasite interactions in each stage of the Plasmodium life cycle and the downstream ramifications on the host’s metabolism, pathogenesis and disease. Such data can become integrated with other large datasets generated using top-down systems biology approaches and be utilised by computational biologists to develop and enhance models of malaria pathogenesis relevant for identifying new drug targets or intervention strategies. Here, we focus on the promise of metabolomics to complement systems biology approaches in the quest for novel interventions in the fight against malaria. We introduce the Malaria Host-Pathogen Interaction Center (MaHPIC), a new systems biology research coalition. A primary goal of the MaHPIC is to generate systems biology datasets relating to human and non-human primate (NHP) malaria parasites and their hosts making these openly available from an online relational database. Metabolomic data from NHP infections and clinical malaria infections from around the world will comprise a unique global resource.     

Antimicrobial and host-defense peptides as new anti-infective therapeutic strategies

Short cationic amphiphilic peptides with antimicrobial and/or immunomodulatory activities are present in virtually every life form, as an important component of (innate) immune defenses. These host-defense peptides provide a template for two separate classes of antimicrobial drugs. Direct-acting antimicrobial host-defense peptides can be rapid-acting and potent, and possess an unusually broad spectrum of activity; consequently, they have prospects as new antibiotics, although clinical trials to date have shown efficacy only as topical agents. But for these compounds to fulfill their therapeutic promise and overcome clinical setbacks, further work is needed to understand their mechanisms of action and reduce the potential for unwanted toxicity, to make them more resistant to protease degradation and improve serum half-life, as well as to devise means of manufacturing them on a large scale in a consistent and cost-effective manner. In contrast, the role of cationic host-defense peptides in modulating the innate immune response and boosting infection-resolving immunity while dampening potentially harmful pro-inflammatory (septic) responses gives these peptides the potential to become an entirely new therapeutic approach against bacterial infections.     

Role of antimicrobial peptides in host defense against mycobacterial infections

Worldwide, tuberculosis remains the most important infectious disease causing morbidity and death. Currently, at least one-third of the world's population is infected with Mycobacterium tuberculosis. In addition, the World Health Organization estimates that about 8-10 million new tuberculosis cases occur annually worldwide and this incidence is currently increasing. Moreover, multidrug-resistant tuberculosis has been increasing in incidence in many areas during the past decade. These situations underscore the importance of the development of new therapeutic agents against mycobacterial infectious diseases. In this article, it is review current progress in the understanding of antimicrobial peptides as potential candidates to develop an alternative/adjunct therapeutic strategy against tuberculosis. This immunoadjunctive therapy might be evaluated in the context of possible drug resistance. This review also summarizes the knowledge about the functions of antimicrobial peptides in the pulmonary innate host defense system and their role in mycobacterial infection, and at the same time outlines recent advances in our understanding of the combined effect of antimicrobial peptides and anti-tuberculosis drugs against intracellular mycobacteria. A concerted effort should now focus on the clinical application of antimicrobial peptides for their practical use.     

The bacterial surface layer provides protection against antimicrobial peptides

This report describes a previously unrecognized role for bacterial surface layers as barriers that confer protection against antimicrobial peptides. As antimicrobial peptides exist in natural environments, S-layers may provide a bacterial survival mechanism that has been selected for through evolution.     

Medicinal plants in the fight against leishmaniasis

Despite the tremendous progress mode in the understanding o f the molecular biology of Leishmania and the clinical possibilities presented by some experimental chemotherapeutic agents, no new drugs have been developed for the treatment of leishmaniasis since the introduction of the pentovalent antimoniols more than 50 years ago. As reviewed here by Maurice M. Iwu, Joan E. Jackson and Brion G. Schuster, recognition of the current extensive use of herbal therapy in Leishmania-endemic regions has renewed interest in evaluation of plant remedies used in traditional medicine as sources of potential antileishmanials.     

Antimicrobial peptides: properties and applicability

All organisms need protection against microorganisms, e. g. bacteria, viruses and fungi. For many years, attention has been focused on adaptive immunity as the main antimicrobial defense system. However, the adaptive immune system, with its network of humoral and cellular responses is only found in higher animals, while innate immunity is encountered in all living creatures. The turning point in the appreciation of the innate immunity was the discovery of antimicrobial peptides in the early eighties. In general these peptides act by disrupting the structural integrity of the microbial membranes. It has become clear that membrane-active peptides and proteins play a crucial role in both the innate and the adaptive immune system as antimicrobial agents. This review is focused on the functional and structural features of the naturally occurring antimicrobial peptides, and discusses their potential as therapeutics.     

Antimicrobial peptides (AMP) with antiviral activity against fish nodavirus

Nervous necrosis virus (NNV) is classified as betanodavirus of Nodaviridae, and has caused mass mortality of numerous marine fish species at larval stage. Antimicrobial peptides (AMPs) play an important role of innate immunity either against bacterial pathogens or viruses. Up to date, little is known if any AMP could effectively inhibit fish nodaviruses and its mechanism. In this study, the antiviral activities of three antimicrobial peptides (AMPs) against grouper NNV (GNNV) were screened in the fish cell line. Two of the three AMPs, tilapia hepcidin 1-5 (TH 1-5) and cyclic shrimp anti-lipopolysaccharide factor (cSALF), were able to agglutinate purified NNV particles into clump, and the clumps were further confirmed to be viral proteins by TEM and Western blot. The NNV solution, separately pre-mixed with AMP (TH 1-5 or cSALF) or deionized-distilled water for 1 h, was used to infect GF-1 cells, and the levels of capsid protein in the GNNV-AMP-infected cells at 1 h post infection were much lower than that in the GNNV-H₂O-infected cells, indicating that only a small portion of viral particles in the GNNV-AMP mixture could successfully infected the cells. Treatment of cBB cells with TH 1-5 and cSALF did not induce Mx gene expression; however, grouper epinecidin-1 (CP643-1) could induce the expression of Mx in the pre-treated cBB cells. This study revealed three AMPs with anti-NNV activity through two different mechanisms, and shed light on the future application in aquaculture.