Escherichia coli ghost production by expression of lysis gene E and Staphylococcal nuclease

Bacteriophage-encoded protein utilization in bacterial ghost production: a mini-review

Bacterial ghosts (BGs) are described as bacterial cell envelopes that retain their structure but lack cytoplasmic contents. The study of BGs spans multiple disciplinary domains, and the development of BG production techniques to obtain ample and stable BG samples holds significant implications for probing the biological characteristics of BGs, devising novel disease treatment strategies, and leveraging their industrial applications. Numerous products encoded within bacteriophage (phage) genomes possess the capability to lyse bacteria, thereby inducing BG formation primarily via disruption of bacterial cell wall integrity. This review comprehensively surveys the utilization of phage-encoded proteins in BG production techniques, encompassing methodologies such as phage E protein-mediated lysis, perforin protein-induced lysis, and strategies combining E protein with holin-endolysin systems. Additionally, discussions and summaries are provided on the current applications, challenges, and modification strategies associated with different techniques. Through a focused exploration of BG production techniques, with an emphasis on precise manipulation of BG formation using phage-encoded protein technologies, this study aims to furnish robust tools and methodologies for delving into the mechanisms underlying BG formation, as well as for the development of novel therapeutic strategies and applications based on BGs.

Recent Update on Bacteria as a Delivery Carrier in Cancer Therapy: From Evil to Allies

Cancer is associated with a comprehensive burden that significantly affects patient’s quality of life. Even though patients’ disease condition is improving following conventional therapies, researchers are studying alternative tools that can penetrate solid tumours to deliver the therapeutics due to issues of developing resistance by the cancer cells. Treating cancer is not the only the goal in cancer therapy; it also includes protecting non-cancerous cells from the toxic effects of anti-cancer agents. Thus, various advanced techniques, such as cell-based drug delivery, bacteria-mediated therapy, and nanoparticles, are devised for site-specific delivery of drugs. One of the novel methods that can be targeted to deliver anti-cancer agents is by utilising genetically modified non-pathogenic bacterial species. This is due to the ability of bacterial species to multiply selectively or non-selectively on tumour cells, resulting in biofilms that leads to disruption of metastasis process. In preclinical studies, this technology has shown significant results in terms of efficacy, and some are currently under investigation. Therefore, researchers have conducted studies on bacteria transporting the anti-cancer drug to targeted tumours. Alternatively, bacterial ghosts and bacterial spores are utilised to deliver anti-cancer drugs. Although in vivo studies of bacteria-mediated cancer therapy have shown successful outcome, further research on bacteria, specifically their targeting mechanism, is required to establish a complete clinical approach in cancer treatment. This review has focused on the up-to-date understanding of bacteria as a therapeutic carrier in the treatment of cancer as an emerging field.

Protective Immunity against Listeria monocytogenes in Rats, Provided by HCl- and NaOH-Induced Listeria monocytogenes Bacterial Ghosts (LMGs) as Vaccine Candidates

Listeria monocytogenes (Lm) bacterial ghosts (LMGs) were produced by the minimum inhibitory concentration (MIC) of HCl, H₂SO₄, and NaOH. Acid and alkali effects on the LMGs were compared by in vitro and in vivo analyses. Scanning electron microscope showed that all chemicals form lysis pores on the Lm cell envelopes. Real-time qPCR revealed a complete absence of genomic DNA in HCl- and H₂SO₄-induced LMGs but not in NaOH-induced LMGs. HCl-, H₂SO₄- and NaOH-induced LMGs showed weaker or missing protein bands on SDS-PAGE gel when compared to wild-type Lm. Murine macrophages exposed to the HCl-induced LMGs showed higher cell viability than those exposed to NaOH-induced LMGs or wild-type Lm. The maximum level of cytokine expression (TNF-α, iNOS, IFN-γ, and IL-10 mRNA) was observed in the macrophages exposed to NaOH-induced LMGs, while that of IL-1β mRNA was observed in the macrophages exposed to HCl-induced LMGs. To investigate LMGs as a vaccine candidate, mice were divided into PBS buffer-injected, HCl- and NaOH-induced LMGs immunized groups. Mice vaccinated with HCl- and NOH-induced LMGs, respectively, significantly increased in specific IgG antibodies, bactericidal activities of serum, and CD4⁺ and CD8⁺ T-cell population. Antigenic Lm proteins reacted with antisera against HCl- and NOH-induced LMGs, respectively. Bacterial loads in HCl- and NaOH-induced LMGs immunized mice were significantly lower than PBS-injected mice after virulent Lm challenges. It suggested that vaccination with LMGs induces both humoral and cell-mediated immune responses and protects against virulent challenges.

Immunization of chickens with Salmonella gallinarium ghosts expressing Salmonella Enteritidis NFliC-FimAC and CD40LC fusion antigen enhances cell-mediated immune responses and protects against wild-type challenges with both species

This study describes the construction and immunological characterization of a novel Salmonella gallinarium ghost vaccine to protect against S. gallinarium (SG) and S. Enteritidis (SE) serotypes. The SG ghost was designed to express N-terminus FliC (D0-D1 domain) and FimA retrieved from the SE genome, and the receptor-binding domain (RBD) of CD40L from the chicken as a single fusion construct. The construct was built in pJHL184, a phage lysis gene E-mediated ghost plasmid and the expression was confirmed by western blot resulting in an 85-kDa band. Chicken immunization was conducted by intramuscular route with SG ghost FliC-FimA-CD40L, vector control, or PBS alone in a prime-boost schedule. Antibody responses, cell-mediated immune responses (CMI), and cytokine induction was assessed in chicken demonstrating significantly high levels of IgY, CMI, cytokine responses in ghost immunized group delivering partial protection against SG wild type challenge and near complete protection against SE challenge wild type challenge.

Production of inactivated gram-positive and gram-negative species with preserved cellular morphology and integrity

There are many approaches available to produce inactive bacteria by termination of growth, each with a different efficacy, impact on cell integrity, and potential for application in standardized inactivation protocols. The aim of this study was to compare these approaches and develop a standardized protocol for generation of inactivated Gram-positive and Gram-negative bacteria, yielding cells that are metabolically dead with retained cellular integrity i.e., preserving the surface and limited leakage of intracellular proteins and DNA. These inactivated bacteria are required for various applications, for instance, when investigating receptor-triggered signaling or bacterial contact-dependent analysis of cell lines requiring long incubation times. We inactivated eight different bacterial strains of different species by treatment with beta-propiolactone, ethanol, formalin, sodium hydroxide, and pasteurization. Inactivation efficacy was determined by culturing, and cell wall integrity assessed by quantifying released DNA, bacterial membrane and intracellular DNA staining, and visualization by scanning electron microscopy. Based on these results, we discuss the bacterial inactivation methods, and their advantages and disadvantages to study host-microbe interactions with inactivated bacteria.

Design, development, and evaluation of the efficacy of a nucleic acid-free version of a bacterial ghost candidate vaccine against avian pathogenic E. coli (APEC) O78:K80 serotype

One of the major bacterial infectious diseases in the poultry industry is avian pathogenic Escherichia coli (APEC), which causes colibacillosis in chickens. To develop a novel nucleic acid-free bacterial ghost (BG) vaccine against the O78:K80 serotype of APEC, in this study we constructed a plasmid that harbored E-lysis and S nuclease (SNUC). Following the expression, the O78:K80 bacteria lost all of their cytoplasmic content and nucleic acids by enzymatic digestion. The functionality of these two proteins in the production procedure of bacterial ghosts was confirmed by monitoring the number of colonies, scanning electron microscopy imaging, gel electrophoresis of genomic DNA, and qPCR on the plasmid content of bacterial ghosts. The protective efficacy of the ghost vaccine generated from O78:K80 serotype of APEC was tested in chickens by injection and inhalation routes and compared with that in chickens that received the injection of a killed vaccine. The O78:K80 BG vaccine candidate, used as injection and inhalation, in comparison with the killed vaccine, triggered higher proinflammatory cytokine expression including IL-6, IL-1β, and TNFSF15; a higher level of antibody-dependent humoral (IgY and IgA) and cellular immune responses (IFNγ and lymphocyte proliferation); and lower lesion scores. According to the results of this study, we suggest that the bacterial ghost technology has the potential to be applied for the development of novel vaccines against avian colibacillosis. This technology provides an effective and reliable approach to make multivalent vaccines for more prevalent APEC strains involved in the establishment of this infectious disease in the poultry industry.

Use of a model to understand the synergies underlying the antibacterial mechanism of H2O2-producing honeys

Honey has been valued as a powerful antimicrobial since ancient times. However, the understanding of the underlying antibacterial mechanism is incomplete. The complexity and variability of honey composition represent a challenge to this scope. In this study, a simple model system was used to investigate the antibacterial effect of, and possible synergies between, the three main stressors present in honey: sugars, gluconic acid, and hydrogen peroxide (H₂O₂), which result from the enzymatic conversion of glucose on honey dilution. Our results demonstrated that the synergy of H₂O₂ and gluconic acid is essential for the antibacterial activity of honey. This synergy caused membrane depolarization, destruction of the cell wall, and eventually growth inhibition of E. coli K-12. The presence of H₂O₂ stimulated the generation of other long-lived ROS in a dose-dependent manner. Sugars caused osmosis-related morphological changes, however, decreased the toxicity of the H₂O₂/gluconic acid. The susceptibility of catalase and general stress response sigma factor mutants confirmed the synergy of the three stressors, which is enhanced at higher H₂O₂ concentrations. By monitoring cellular phenotypic changes caused by model honey, we explained how this can be bactericidal even though the antimicrobial compounds which it contains are at non-inhibitory concentrations.

Cloning of hok gene into anhydrotetracycline inducible pASK75 vector reveals potent antimicrobial effect of 19 amino acid long N-terminal fragment of hok peptide

An important toxin-antitoxin (TA) system hok/sok, encoded by R1 plasmid of Escherichia coli, is involved in the post segregation killing of cells that have lost the plasmid. The lethal properties of hok protein have been utilized for the environmental containment of microbes and the development of potential vaccine candidates. This study aimed to demonstrate the potent anti-microbial property of a 19 amino acid (AA) long N-terminal fragment of hok peptide. This was accomplished by designing a conditional suicide system based on hok gene expression cloned in an anhydrotetracycline (aTc) inducible vector - pASK75. Heat shock and electroporation were utilized for the transformation of Escherichia coli and Vibrio cholerae cells, respectively. The minimal induction concentration (MI_d C) of aTc, determined by analyzing the expression of green fluorescent protein cloned separately into pASK75 vector, was 30 ng/mL. As hok gene was synthesized de novo (using recombinant polymerase chain reaction) in our study, various random sized hok fragments were generated (as a result of the error-prone nature of Taq polymerase). The smallest hok fragment able to bring about effective antimicrobial killing was a 19 AA long N-terminal fragment of hok having the wild type sequence, except for the carboxy terminus AA residue. The MI_d C of aTc in our experiments was 6-fold lower than previously reported, making our bacterial clones suitable for use in mammalian systems as potential vaccine candidates. Based on our experiments, we hypothesize the 19 AA long N-terminal fragment of hok peptide to be the smallest possible hok fragment sufficient to bring about effective antimicrobial killing.

Potential of Bacteriocins from Lactobacillus taiwanensis for Producing Bacterial Ghosts as a Next Generation Vaccine

Bacteriocins are functionally diverse toxins produced by most microbes and are potent antimicrobial peptides (AMPs) for bacterial ghosts as next generation vaccines. Here, we first report that the AMPs secreted from Lactobacillus taiwanensis effectively form ghosts of pathogenic bacteria and are identified as diverse bacteriocins, including novel ones. In detail, a cell-free supernatant from L. taiwanensis exhibited antimicrobial activities against pathogenic bacteria and was observed to effectively cause cellular lysis through pore formation in the bacterial membrane using scanning electron microscopy (SEM). The treatment of the cell-free supernatant with proteinase K or EDTA proved that the antimicrobial activity is mediated by AMPs, and the purification of AMPs using Sep-Pak columns indicated that the cell-free supernatant includes various amphipathic peptides responsible for the antimicrobial activity. Furthermore, the whole-genome sequencing of L. taiwanensis revealed that the strain has diverse bacteriocins, confirmed experimentally to function as AMPs, and among them are three novel bacteriocins, designated as Tan 1, Tan 2, and Tan 3. We also confirmed, using SEM, that Tan 2 effectively produces bacterial ghosts. Therefore, our data suggest that the bacteriocins from L. taiwanensis are potentially useful as a critical component for the preparation of bacterial ghosts.

The development of ghost vaccines trials

INTRODUCTION

Bacterial ghosts are intact bacterial cell envelopes that are emptied of their content by gentle biological or chemical poring methods. Ghost techniques increase the safety of the killed vaccines, while maintaining their antigenicity due to mild preparation procedures. Moreover, ghost-platforms may express and/or carry several antigens or plasmid-DNA encoding for protein epitopes.

AREAS COVERED

In this review, the development in ghost-vaccine production over the last 30 years is classified and discussed. The different applications of ghost-vaccines, how they trigger the immune system, their advantages and limitations are displayed. The phage-mediated lysis, molecular manipulation of the lysis-genes, and the biotechnological production of ghosts are described. The trials are classified according to the pattern of lysis and to the type of bacteria. Further subdivision includes chronological ordered application of the ghost as alternative-killed vaccine, recombinant antigen platform, plasmid DNA carrier, adjuvants, and dendritic cell inducer. Particular trials for specific pathogens or from distinct research schools are gathered.

EXPERT OPINION

Ghosts are highly qualified to act as immune-presenting platforms that express and/or carry several recombinant and DNA vaccines, as well as, being efficient alternative-killed vaccines. The coming years will show more molecular advances to develop ghost-production and to express more antigens.

Bacteriosomes as a Promising Tool in Biomedical Applications: Immunotherapy and Drug Delivery

Bacteriosomes are a member of cell-derived vesicles that are proposed as promising tools in diagnosis, therapy, and drug delivery. These vesicles could be derived from a virus, bacterial cells, and animal cells. Biotechnology techniques were used in bioengineering of cell-derived vesicles in vitro, and in vivo. Bacterial vesicles such as bacterial cells, bacterial ghost, or bacteriosomes are vesicular structures derived from bacteria produced by manipulation of bacterial cells by chemical agents or gene-mediated lysis. Subsequently, bacterial vesicles (bacteriosomes) are non-living, non-denatured bacterial cell envelopes free of the cytoplasm and genetic materials. Gram-negative and Gram-positive bacteria are exploited in the production of bacteriosomes. Bacteriosomes have instinct organs, tissues, cells, as well as subcellular tropism. Moreover, bacteriosomes might be used as immunotherapy and/or drug delivery shuttles. They could act as cargoes for the delivery of small drugs, large therapeutics, and nanoparticles to the specific location. Furthermore, bacteriosomes have nature endosomal escaping ability, hence they could traffic different bio-membranes by endocytosis mechanisms. Therefore, bacterial-derived vesicles could be used in therapy and development of an innovative drug delivery systems. Consequently, utilizing bacteriosomes as drug cargoes enhances the delivery and efficacy of administered therapeutic agents. This review highlighted bacteriosomes in terms of source, engineering, characterization, applications, and limitations.

Salmonella Enteritidis ghost vaccine carrying the hemagglutinin globular head (HA1) domain from H1N1 virus protects against salmonellosis and influenza in chickens

This study evaluated the attenuated Salmonella Enteritidis (SE) ghost strain JOL2114 (Δlon ΔcpxR Δasd), which displays on the bacterial surface the H1N1 hemagglutinin globular head portion (HA1; amino acid residues 63-286) on the bacterial surface for protective efficacy against Salmonella and H1N1 challenge in the chicken model, as the birds are the predominant reservoirs for both diseases. The ghost system enhanced the lysis process by converging two lysis processes found in bacteriophages: bacteriophage PhiX174 lysis gene E and holin-endolysin genes found in bacteriophage λ, complemented with accessory lysis-related proteins Rz/Rz1. The present lysis machinery resulted in complete lysis of host-attenuated SE strains in about 24 hrs of incubation under a non-permissible temperature of 42 °C in the absence of L-arabinose, an antisense inducer that blocks lysis gene expression during the growth phase. SE ghost JOL2114 surface display of HA1 was confirmed by Western blot analysis resulting in an immune-reactive band of 31 kDa in size. Chicken immunization via intramuscular and oral routes yielded both SE and HA1 antigen-specific immune responses. Protective humoral and cell-mediated immune responses were effectively elicited against both Salmonella and influenza challenge. This efficient strategy of ghost generation employs a dual system of phage lysis for biological generation of SE ghosts that preserves the surface antigenic architecture, offering a rapid and effective way to generate vaccines that could be deployed in urgent circumstances to protect against both Salmonella and influenza infection.

Harnessing the Immunomodulatory Properties of Bacterial Ghosts to Boost the Anti-mycobacterial Protective Immunity

Tuberculosis (TB) pathogenesis is characterized by inadequate immune cell activation and delayed T cell response in the host. Recent immunotherapeutic efforts have been directed at stimulating innate immunity and enhancing interactions between antigen presenting cells and T cells subsets to improve the protective immunity against TB. In this study, we investigated the immunostimulatory properties of bacterial ghosts (BG) as a novel approach to potentiate the host immunity against mycobacterial infection. BG are intact cytoplasm-free Escherichia coli envelopes and have been developed as bacterial vaccines and adjuvant/delivery system in cancer immunotherapy. However, BG have yet to be exploited as immunopotentiators in the context of infectious diseases. Here, we showed that BG are potent inducers of dendritic cells (DC), which led to enhanced T cell proliferation and differentiation into effector cells. BG also induced macrophage activation, which was associated with enhanced nitric oxide production, a key anti-mycobacterial weapon. We further demonstrated that the immunostimulatory capability of BG far exceeds that of LPS and involves both TLR4-dependent and independent pathways. Consistently, BG treatment, but not LPS treatment, reduced the bacterial burden in infected mice, which correlated with increased influx of innate and adaptive effector immune cells and increased production of key cytokines in the lungs. Finally and importantly, enhanced bacilli killing was seen in mice co-administered with BG and second-line TB drugs bedaquiline and delamanid. Overall, this work paves the way for BG as potent immunostimulators that may be harnessed to improve mycobacteria killing at the site of infection.

Exogenous melatonin confers drought stress by promoting plant growth, photosynthetic capacity and antioxidant defense system of maize seedlings

Melatonin is an important biologically active hormone that plays a vital role in plant growth and development. In particular, it has been investigated for its roles in abiotic stress management. The current experiment was carried out to investigate the protective role of melatonin in photosynthetic traits and the antioxidant defense system of maize seedling under drought stress. Maize seedlings were subjected to drought stress (40–45% FC) after two weeks of seedling emergence, followed by a foliar spray (0, 25, 50, 75 and 100 µM) and soil drench of melatonin (0, 25, 50, 75 and 100 µM). Our results indicated that drought stress negatively affected maize seedling and decreased plant growth and development, biomass accumulation, reduced chlorophyll, and carotenoid content, and significantly declined photosynthetic rate and stomatal conductance. On the other hand, reactive oxygen species, soluble protein, and proline content increased under drought stress. However, the application of exogenous melatonin reduced the reactive oxygen species burst and enhanced the photosynthetic activity by protecting from damages through activation of various antioxidant enzymes under drought stress. Foliar application of 100 µM and soil drench of 50 µM melatonin was the most effective treatment concentrations under drought stress. Our current findings hereby confirmed the mitigating potential of melatonin application for drought stress by maintaining plant growth, improving the photosynthetic characteristics and activities of antioxidants enzymes.

The design and application of a bacterial ghost vaccine to evaluate immune response and defense against avian pathogenic Escherichia coli O2:K1 serotype

An Escherichia coli (E. coli) O2:K1 bacterial ghost was produced by controlled expression of bacteriophage PhiX 174 lysis gene E. Temperature controlled expression of this gene caused tunnels and holes in the cell wall of E. coli O2:K1 bacterium, leading to loss of cytoplasmic contents. Formation of E. coli O2:K1 ghost was confirmed by scanning electron microscopy and determination of colony forming units. To evaluate the efficiency of this bacterial ghost vaccine to elicit cellular and humoral immune responses, 85 one day old chickens from Ross 308 breed were divided into the following 5 groups; group 1 (non-immunized control), group 2 (vaccine administered by injection of E. coli O2:K1 killed vaccine), group 3 (vaccine administered by injection of E. coli O2:K1 ghost), group 4 (vaccine administered by inhalation of E. coli O2:K1 ghost), and group 5 (neither immunized, nor challenged as negative control). The groups of 2, 3, and 4 were received vaccines at days 7, 14, and 22. Groups 1 to 4 were challenged with the wild type at day 33. Evaluation of post-mortem lesions and immune responses in all groups showed that chicken injected with the killed vaccine and the bacterial ghost had the best protection. These findings suggest that this bacterial ghost has the potential to be used as a poultry colibacillosis vaccine.

A novel autolysis system for extracellular production and direct immobilization of a phospholipase D fused with cellulose binding domain

Background

Several types of phospholipases have been described in phospholipids modification. The majority of phospholipase D (PLD) superfamily members can catalyze two separate reactions: the hydrolysis of phospholipids to produce phosphatidic acid (PA) and the transphosphatidylation of phosphatidyl groups into various phosphatidyl alcohols to produce modified phospholipids. Transphosphatidylation is a useful biocatalytic method for the synthesis of functional phospholipids from lecithin or phosphatidylcholine (PC), which are both easily accessible. Different PLD coding genes have been cloned from various sources from viral, prokaryotic, and eukaryotic organisms. Despite the catalytic potential of PLD, their low productivity has hampered their practical applications, probably because PLD, which is highly toxic to the host cells, when transformation of the PLD genes into the host cells, degrade PLs in the cell membrane. In this study, we designed a novel two-step expression system to produce and secrete recombinant PLD in extracellular medium, cellulose-binding domains as an affinity fused with PLD for immobilization and purification proteins.

Results

The engineered BL21 (DE3) host strain, which harbored the final expression vector pET28a-PLD-CBD-araC-ESN, was induced by IPTG and L-arabinose, the cell density decreased rapidly over a 2 h period and the enzymes released into the extracellular medium accounts owned 81.75% hydrolytic activity. Scanning electron microscopy results showed that there were obvious structural changes on the cell surface. The extracellularly secreted PLD-CBD powder was used to catalyze the transphosphatidylation reaction synthesis of phosphatidylserine, 2.3 U enzymes reacted for 12 h, during which the conversion rate reached 99% with very few by-products being produced. When the fused protein PLD-CBD immobilized on microcrystalline cellulose, the enzymes can be cycle used five times with 26% conversion rate was preserved.

Conclusions

This study introduced an effective method for use in the expression of recombinant proteins and their extracellular secretion that simplifies the steps of sonication and purification and demonstrates great potential in the industrial application of enzymes. Cellulose as the most abundant renewable biomass resources in nature, and the cost is low, used for PLD immobilization make it more simple, effective and sustainable.

Use of a modified bacterial ghost lysis system for the construction of an inactivated avian pathogenic Escherichia coli vaccine candidate

Vaccination is an effective strategy to prevent avian colibacillosis. Bacterial ghosts (BGs) are prepared by the controlled expression of the phiX174 gene E, which mediates the lysis of Gram-negative bacteria. Staphylococcal nuclease A may be used to produce BGs for further inactivation of host bacteria and elimination of residual genetic material. In this study, the double promoter lysis plasmid (pUC19-ΔcI857-E-rrnB-pL-SN) was successfully constructed and BGs were prepared at 37 °C. The cleavage efficiency of Escherichia coli BGs was 99.9%. Furthermore, to evaluate the immunological effects of the BG vaccines in chickens, a BG vaccine was prepared using the serotype O2 avian pathogenic Escherichia coli deletion strain (DE17ΔluxSΔaroA). The results showed that the BG vaccine was able to achieve over 90% immune protection against virulent challenge using the same serotype O2 strain (DE17 or CE35), while it showed poor cross-protection against serotypes O1 and O78 (data not shown). The enzyme-linked immunosorbent assay results showed that the antibody levels in the immunized groups were higher than in the control group (p < 0.05), with the BG group being the highest. The cytokine tests showed that the levels of interferon-γ in the BG immune group were higher than in the phosphate-buffered saline (PBS) control group (non-immune) (p < 0.01) and the formalin-inactivated vaccine immune group (p < 0.05), and the levels of tumor necrosis factor-α in the BG group were higher than in the formalin-inactivated vaccine (p > 0.05) and the PBS control groups (p < 0.05). In addition, pathological analysis revealed that the PBS control group showed typical fibrinous pericarditis and perihepatitis, whereas the immune group showed no obvious pathological changes. In summary, our findings provide a new strategy for the prevention and control of avian colibacillosis.

Bacterial ghost of avian pathogenic E. coli (APEC) serotype O78:K80 as a homologous vaccine against avian colibacillosis

Avian Colibacillosis is among the major causes of economic loss in the poultry industry worldwide, with a more vivid impact on developing countries. The involvement of several bacteria has made it challenging to develop effective vaccines for this disease, particularly because it is notoriously difficult to make a vaccine that contains all the contributing pathogenic bacteria. Here, we report the design and fabrication of a bacterial ghost (BG) of E. coli O78:K80, which is among the major bacterial serotypes responsible for this disease. The generated ghost is then exploited as a homologous vaccine against Avian Colibacillosis. We demonstrate that hole formation in the cell wall of E. coli O78:K80 can happen properly in optical densities as high as 0.8 compared to the 0.3–0.4 standard for bacteria like E. coli TOP10. This is especially advantageous for mass production of this ghost which is a vital factor in development of any BG-based vaccine. Compared to E. coli TOP10, we faced a great challenge in transforming the wild type bacteria with the E-lysis plasmid which was probably due to higher thickness of the cell wall in O78:K80. This, however, was addressed by treating the cell wall with a different combination of ions.The vaccine was administered to Ross 308 broiler chickens via injection as well as through their respiratory system at a dose of 1010 BGs, repeated 3 times at weekly intervals. Chickens were then challenged with the wild type O78:K80 at a dose of 1011 bacteria together with Infectious Bronchitis H120 vaccine (as immunosuppressant) one week after the last immunization. Air sac lesions were significantly reduced in BG vaccinated groups in comparison with the control group. The levels of IFNγ, IgA and IgY were measured in the serum of immunized chickens as an indication of immune response and were compared with those of the chickens vaccinated with killed bacteria. The results show that O78:K80 BG can be used as an efficient homologous vaccine against Colibacillosis disease in poultry. We expect our findings can serve as the starting point for designing more sophisticated vaccines that contain all three major pathogenic bacteria involved in avian Colibacillosis.

A novel protocol for bacterial ghosts' preparation using tween 80

Bacterial ghosts (BGs) can be prepared by both genetic and chemical means. Genetic method include using lysis gene E. Chemical method include incubation with numerous agents for a short time at their minimum inhibitory or minimum growth concentrations (MIC or MGC). The aim of this study is to prepare the BGs with a new protocol via exposing the bacterial cells to tween 80 for an extended period of time followed by sudden reduction of the surrounding pH. Salmonella enterica serovar typhimurium ATCC 13311 was used for this purpose. The cells were incubated in 7% v/v tween 80 solution in Muller-Hinton broth for 24 h at 37 °C then pH was decreased to 3.6 by adding lactic acid for one hour. The bacterial pellets were separated by high speed centrifugation, and then washed three times by half normal saline solution. High quality BGs were visualized by scanning electron microscopy (SEM) revealing punctured cells with intact outer shells and at least one intramembranous tunnel. The absence of vital cells was confirmed by subculturing. The release of respective amounts of proteins and DNA is another evidence of ghost's production. In addition, the integrity of cells was proved by visualization of Gram-stained cells using light microscopy. In conclusion, this new protocol is simple, economic and feasible for BGs preparation.

Bacterial ghosts as adjuvants: mechanisms and potential

Bacterial ghosts (BG) are empty cell envelopes derived from Gram-negative bacteria. They contain many innate immunostimulatory agonists, and are potent activators of a broad range of cell types involved in innate and adaptive immunity. Several considerable studies have demonstrated the effectiveness of BG as adjuvants as well as their ability to induce proinflammatory cytokine production by a range of immune and non-immune cell types. These proinflammatory cytokines trigger a generalized recruitment of T and B lymphocytes to lymph nodes that maximize the chances of encounter with their cognate antigen, and subsequent elicitation of potent immune responses. The plasticity of BG has allowed for the generation of envelope-bound foreign antigens in immunologically active forms that have proven to be effective vaccines in animal models. Besides their adjuvant property, BG also effectively deliver DNA-encoded antigens to dendritic cells, thereby leading to high transfection efficiencies, which subsequently result in higher gene expressions and improved immunogenicity of DNA-based vaccines. In this review, we summarize our understanding of BG interactions with the host immune system, their exploitation as an adjuvant and a delivery system, and address important areas of future research interest.

Protective immunity of grass carp induced by DNA vaccine encoding capsid protein gene (vp7) of grass carp reovirus using bacterial ghost as delivery vehicles

Grass carp reovirus (GCRV) is one of the most pathogenic aquareovirus and can cause lethal hemorrhagic disease in grass carp (Ctenopharyngodon idella). However, management of GCRV infection remains a challenge. Therefore, it is necessary to find effective means for the control of its infection. The uses of bacterial ghost (BG, non-living bacteria) as carriers for DNA delivery have received considerable attentions in veterinary and human vaccines studies. Nevertheless, there is still no report about intramuscular administration of bacterial ghost-based DNA vaccines in fish. In the current study, a novel vaccine based on Escherichia coli DH5α bacterial ghost (DH5α-BG), delivering a major capsid protein gene (vp7) of grass carp reovirus encoded DNA vaccine was developed to enhance the efficacy of a vp7 DNA vaccine against GCRV in grass carp. The grass carp was injected intramuscularly by different treatments -i) naked pcDNA-vp7 (containing plasmid 1, 2.5 and 5 μg, respectively), ii) DH5α-BG/pcDNA-vp7 (containing plasmid 1, 2.5 and 5 μg, respectively) and iii) naked pcDNA, DH5α-BG or phosphate buffered saline. The immune responses and disease resistance of grass carp were assessed in different groups, and results indicated that the antibody levels, serum total antioxidant capacity (T-AOC), superoxide dismutase (SOD) activity, acid phosphatase (ACP) activity and alkaline phosphatase (AKP) activity and immune-related genes were significantly enhanced in fish immunized with DH5α-BG/pcDNA-vp7 vaccine (DNA dose ranged from 2.5 to 5 μg). In addition, the relative percentage survival were significantly enhanced in fish immunized with DH5α-BG/pcDNA-vp7 vaccine and the relative percentage survival reached to 90% in DH5α-BG/pcDNA-vp7 group than that of naked pcDNA-vp7 (42.22%) at the highest DNA dose (5 μg) after 14 days of post infection. Moreover, the level of pcDNA-vp7 plasmid was higher in DH5α-BG/pcDNA-vp7 groups than naked pcDNA-vp7 groups in muscle and kidneys tissues after 21 days. Overall, those results suggested that DH5α bacterial ghost based DNA vaccine might be used as a promising vaccine for aquatic animals to fight against GCRV infection.

Improved lysis efficiency and immunogenicity of Salmonella ghosts mediated by co-expression of λ phage holin-endolysin and ɸX174 gene E

Bacterial ghosts (BGs) are empty cell envelopes derived from Gram-negative bacteria by bacteriophage ɸX174 gene E mediated lysis. They represent a novel inactivated vaccine platform; however, the practical application of BGs for human vaccines seems to be limited due to the safety concerns on the presence of viable cells in BGs. Therefore, to improve the lysis efficiency of the gene E, we exploited the peptidoglycan hydrolyzing ability of the λ phage holin-endolysins to expedite the process of current BG production system. In this report, we constructed a novel ghost plasmid encoding protein E and holin-endolysins in tandem. We observed that sequential expressions of the gene E and the holin-endolysins elicited rapid and highly efficient Salmonella lysis compared to the lysis mediated by gene E only. These lysed BGs displayed improved immunogenicity in mice compared to the gene E mediated BGs. Consequently, seventy percent of the mice immunized with these novel ghosts survived against a lethal challenge while all the mice vaccinated with gene E mediated ghosts died by day 9 post-infection. We conclude that this novel strategy has the potential to generate highly efficient inactivated candidate vaccines that could replace the currently available bacterial vaccines.

Functional display of ice nucleation protein InaZ on the surface of bacterial ghosts

In a concept study the ability to induce heterogeneous ice formation by Bacterial Ghosts (BGs) from Escherichia coli carrying ice nucleation protein InaZ from Pseudomonas syringae in their outer membrane was investigated by a droplet-freezing assay of ultra-pure water. As determined by the median freezing temperature and cumulative ice nucleation spectra it could be demonstrated that both the living recombinant E. coli and their corresponding BGs functionally display InaZ on their surface. Under the production conditions chosen both samples belong to type II ice-nucleation particles inducing ice formation at a temperature range of between -5.6 °C and -6.7 °C, respectively. One advantage for the application of such BGs over their living recombinant mother bacteria is that they are non-living native cell envelopes retaining the biophysical properties of ice nucleation and do no longer represent genetically modified organisms (GMOs).

Characterization of Chemically-Induced Bacterial Ghosts (BGs) Using Sodium Hydroxide-Induced Vibrio parahaemolyticus Ghosts (VPGs)

Acellular bacterial ghosts (BGs) are empty non-living bacterial cell envelopes, commonly generated by controlled expression of the cloned lysis gene E of bacteriophage PhiX174. In this study, Vibrio parahaemolyticus ghosts (VPGs) were generated by chemically-induced lysis and the method is based on minimum inhibitory concentration (MIC) of sodium hydroxide (NaOH), acetic acid, boric acid, citric acid, maleic acid, hydrochloric acid, and sulfuric acid. The MIC values of the respective chemicals were 3.125, 6.25, <50.0, 25.0, 6.25, 1.56, and 0.781 mg/mL. Except for boric acid, the lysis efficiency reached more than 99.99% at 5 min after treatment of all chemicals. Among those chemicals, NaOH-induced VPGs appeared completely DNA-free, which was confirmed by quantitative real-time PCR. Besides, lipopolysaccharides (LPS) extracted from the NaOH-induced VPGs showed no distinctive band on SDS-PAGE gel after silver staining. On the other hand, LPS extracted from wild-type bacterial cells, as well as the organic acids-induced VPGs showed triple major bands and LPS extracted from the inorganic acids-induced VPGs showed double bands. It suggests that some surface structures in LPS of the NaOH-induced VPGs may be lost, weakened, or modified by the MIC of NaOH. Nevertheless, Limulus amoebocyte lysate assay revealed that there is no significant difference in endotoxic activity between the NaOH-induced VPGs and wild-type bacterial cells. Macrophages exposed to the NaOH-induced VPGs at 0.5 × 10⁶ CFU/mL showed cell viability of 97.9%, however, the MIC of NaOH did not reduce the cytotoxic effect of wild-type bacterial cells. Like Escherichia coli LPS, the NaOH-induced VPGs are an excellent activator of pro-inflammatory cytokines (IL-1β and iNOS), anti-inflammatory cytokine (IL-10), and dual activities (IL-6) in the stimulated macrophage cells. On the other hand, the induction of TNF-α mRNA was remarkable in the macrophages exposed with wild-type cells. Scanning electron microscopy showed the formation of trans-membrane lysis tunnel structures in the NaOH-induced VPGs. SDS-PAGE and agarose gel electrophoresis also confirmed that cytoplasmic proteins and genomic DNA released from the VPGs to culture medium through the lysis tunnel structures. Taken together, all these data indicate that the NaOH-induced VPGs show the potency of a safe, economical, and effective inactivated bacterial vaccine candidate.

In vitro responses of chicken macrophage-like monocytes following exposure to pathogenic and non-pathogenic E. coli ghosts loaded with a rational design of conserved genetic materials of influenza and Newcastle disease viruses

Avian influenza virus (AIV) and Newcastle disease virus (NDV) are two important viral diseases in the poultry industry. Therefore, new disease-fighting strategies, especially effective genetic vaccination, are in high demand. Bacterial Ghost (BG) is a promising platform for delivering genetic materials to macrophages, cells that are among the first to encounter these viruses. However, there is no investigation on the immune response of these macrophage-targeted treatments. Here, we investigated the effect of genetic materials of AIV and NDV on the gene expression profile of important pro-inflammatory cytokines, a chemokine, a transcription factor, major histocompatibility complexes, and the viability of the chicken macrophage-like monocyte cells (CMM). Our genetic construct contained the external domain of matrix protein 2 and nucleoprotein gene of AIV, and immunodominant epitopes of fusion and hemagglutinin-neuraminidase proteins of NDV (hereinafter referred to as pAIV-Vax), delivered via the pathogenic and non-pathogenic BGs (Escherichia coli O78K80 and E. coli TOP10 respectively). The results demonstrated that both types of BGs were able to efficiently deliver the construct to the CMM, although the pathogenic strain derived BG was a significantly better stimulant and delivery vehicle. Both BGs were safe regarding LPS toxicity and did not induce any cell death. Furthermore, the loaded BGs were more powerful in modulating the pro-inflammatory cytokines' responses and antigen presentation systems in comparison to the unloaded BGs. Nitric oxide production of the BG-stimulated cells was also comparable to those challenged by the live bacteria. According to the results, the combination of pAIV-Vax construct and E. coli O78K80 BG is promising in inducing a considerable innate and adaptive immune response against AIV-NDV and perhaps the pathogenic E. coli, provided that the current combination be a potential candidate for in vivo testing regarding the development of an effective trivalent DNA vaccine against avian influenza and Newcastle disease, as well as a bacterial ghost vaccine against avian pathogenic E. coli (APEC).

Bacterial Ghosts of Escherichia coli Drive Efficient Maturation of Bovine Monocyte-Derived Dendritic Cells

Bacterial ghosts (BGs) are empty cell envelopes derived from Gram-negative bacteria. They not only represent a potential platform for development of novel vaccines but also provide a tool for efficient adjuvant and antigen delivery system. In the present study, we investigated the interaction between BGs of Escherichia coli (E. coli) and bovine monocyte-derived dendritic cells (MoDCs). MoDCs are highly potent antigen-presenting cells and have the potential to act as a powerful tool for manipulating the immune system. We generated bovine MoDCs in vitro from blood monocytes using E. coli expressed bovine GM-CSF and IL-4 cytokines. These MoDCs displayed typical morphology and functions similar to DCs. We further investigated the E. coli BGs to induce maturation of bovine MoDCs in comparison to E. coli lipopolysaccharide (LPS). We observed the maturation marker molecules such as MHC-II, CD80 and CD86 were induced early and at higher levels in BG stimulated MoDCs as compared to the LPS stimulated MoDCs. BG mediated stimulation induced significantly higher levels of cytokine expression in bovine MoDCs than LPS. Both pro-inflammatory (IL-12 and TNF-α) and anti-inflammatory (IL-10) cytokines were induced in MoDCs after BGs stimulation. We further analysed the effects of BGs on the bovine MoDCs in an allogenic mixed lymphocyte reaction (MLR). We found the BG-treated bovine MoDCs had significantly (p<0.05) higher capacity to stimulate allogenic T cell proliferation in MLR as compared to the LPS. Taken together, these findings demonstrate the E. coli BGs induce a strong activation and maturation of bovine MoDCs.

Efficient production of safety-enhanced Escherichia coli ghosts by tandem expression of PhiX 174 mutant gene E and staphylococcal nuclease A gene

The application of bacterial ghosts as vaccines is limited because of their low lysis efficiency and production and the presence of pathogenic islands and/or antibiotic resistance genes within ghost preparations. To overcome these problems, a new lysis plasmid with fusion gene of mutant gene E and staphylococcal nuclease A gene (mE-L-SNA) were constructed and characterized. The new plasmid pBV-mELS could efficiently induce the genetic inactivation of Escherichia coli cultures, accompanied by the intracellular degradation of the genetic material of host cells, devoid of the presence of pathogenic islands and antibiotic resistance genes within ghost preparations. Furthermore, the lysis efficiency of the plasmid pBV-mELS was not affected by bacterial concentration and could reach 99.99995% for E. coli at late-log phase. However, when the 74-bp non-encoding region of the gene mE-L-SNA were deleted or the first T nucleotide of the gene mE-L-SNA were substituted, these resulting genes lost the function of bacteriolysis, which suggested the 74-bp region of the gene mE-L-SNA, especially the first T nucleotide, played a crucial role in enhancement of bacteriolysis. The lysis system with the gene mE-L-SNA had predominance for large-scale production of safety-enhanced bacterial ghosts. The strategy may provide a promising avenue for efficient production of safe bacterial ghost vaccines.

Phage lytic proteins: biotechnological applications beyond clinical antimicrobials

Most bacteriophages encode two types of cell wall lytic proteins: endolysins (lysins) and virion-associated peptidoglycan hydrolases. Both enzymes have the ability to degrade the peptidoglycan of Gram-positive bacteria resulting in cell lysis when they are applied externally. Bacteriophage lytic proteins have a demonstrated potential in treating animal models of infectious diseases. There has also been an increase in the study of these lytic proteins for their application in areas such as food safety, pathogen detection/diagnosis, surfaces disinfection, vaccine development and nanotechnology. This review summarizes the more recent developments, outlines the full potential of these proteins to develop new biotechnological tools and discusses the feasibility of these proposals.

Helicobacter pylori outer inflammatory protein DNA vaccine-loaded bacterial ghost enhances immune protective efficacy in C57BL/6 mice

Helicobacter pylori (H. pylori) infection is associated with incidents of gastrointestinal diseases in half of the human population. However, management of its infection remains a challenge. Hence, it is necessary to develop an efficient vaccine to fight against this pathogen. In the present study, a novel vaccine based on the production of attenuated Salmonella typhimurium bacterial ghost (SL7207-BG), delivering H. pylori outer inflammatory protein gene (oipA) encoded DNA vaccine was developed, and the efficiency was evaluated in C57BL/6 mice. Significant higher levels of IgG2a/IgG1 antibodies and IFN-γ/IL-4 cytokines were detected after mice were oral administered with oipA DNA vaccine loaded SL7207-BG, indicating that a mixed Th1/Th2 immune response was elicited. When challenged with infective doses H. pylori strain SS1, the ghost based vaccine was capable of reducing bacterium colonization in the vaccinated mice. In addition, codon-optimized oipA plasmid loaded SL7207-BG significantly eliminates H. pylori colonization density in mice model. Thus, it has been demonstrated that this novel bacterial ghost based DNA vaccine could be used as a promising vaccine candidate for the control of H. pylori infection.

Evaluation the surface antigen of the Salmonella typhimurium ATCC 14028 ghosts prepared by "SLRP"

Recently, bacterial ghosts (BGs) were prepared using a protocol based on critical chemical concentrations. It has been given the name "sponge like" (SL) protocol and used in its reduced form "sponge like reduced protocol" (SLRP). While specific antibody for Salmonella is available on the market under the commercial names (of some kits) such as Febrile Antigen Kit (N.S. BIO-TEC), we used the described Kit to investigate the validity of the SLRP. In this study, using SLRP we succeeded to prepare STGs with correct surface antigens could interact with their specific antibodies. Additionally the study has included oral vaccination with STGs with challenge test. The rats serums have been evaluated against both of the O and H antigens. The antigen-antibody interaction (agglutination) results of both the SLRP and the animal experiments prove that we have correct STGs able to immunize the rats against viable Salmonella. STGs could be used as vaccine and as adjuvant and in the antibodies and in the diagnostic kits production. This study is an additional step for the establishment of correct BGs for immunological purposes.

Generation of a safety enhanced Salmonella Gallinarum ghost using antibiotic resistance free plasmid and its potential as an effective inactivated vaccine candidate against fowl typhoid

A safety enhanced Salmonella Gallinarum (SG) ghost was constructed using an antibiotic resistance gene free plasmid and evaluated its potential as fowl typhoid (FT) vaccine candidate. The antibiotic resistance free pYA3342 plasmid possesses aspartate semialdehyde dehydrogenase gene which is complimentary to the deletion of the chromosomal asd gene in the bacterial host. This plasmid was incorporated with a ghost cassette containing the bacteriophage PhiX174 lysis gene E, designated as pJHL101. The plasmid pJHL101 was transformed into a two virulence genes-deleted SG. The SG ghosts with tunnel formation and loss of cytoplasmic contents were observed by scanning electron microscopy and transmission electron microscopy. The cell viability of the culture solution was decreased to 0% at 24h after the induction of gene E expression by an increase in temperature from 37°C to 42°C. The safety and protective efficacy of the SG ghost vaccine was further examined in chickens which were divided into three groups: group A (non-immunized control), group B (orally immunized), and group C (intramuscularly immunized). The birds were immunized at 7d of age. No clinical symptoms associated with FT such as anorexia, depression and greenish diarrhea were observed in the immunized chickens. Upon challenge with a virulent SG strain at 3 week post-immunization, the chickens immunized with the SG ghost via various routes were efficiently protected, as shown by significantly lower mortality and post-mortem lesions in comparison with control group. In addition, all the immunized chickens showed significantly higher antibody responses accompanied by a potent antigen-specific lymphocyte proliferative response along with significantly increased numbers of CD4⁺ and CD8⁺ T lymphocytes. Overall, our results provide a promising approach of generating SG ghosts using the antibiotic resistance free plasmid in order to prepare a non-living bacterial vaccine candidate which could be environmentally safe yet efficient to prevent FT in chickens.

Development of a biosafety enhanced and immunogenic Salmonella enteritidis ghost using an antibiotic resistance gene free plasmid carrying a bacteriophage lysis system

In the development of genetically inactivated bacterial vaccines, plasmid retention often requires the antibiotic resistance gene markers, the presence of which can cause the potential biosafety hazards such as the horizontal spread of resistance genes. The new lysis plasmid was constructed by utilizing the approach of balanced-lethal systems based on auxotrophic gene Aspartate semialdehyde dehydrogenase (asd). The PhiX174 lysis gene E and λPR37-cI857 temperature-sensitive regulatory system was cloned in the asd gene positive plasmid and this novel approach allowed the production of antibiotic resistance marker free Salmonella Enteritidis (S. Enteritidis) ghost. The immunogenic potential of the biosafety enhanced antibiotic resistance gene free S. Enteritidis ghost was evaluated in chickens by employing the prime-boost vaccination strategy using a combination of oral and intramuscular routes. A total of 75 two-week-old chickens were equally divided into five groups: group A (non-immunized control), group B (intramuscularly primed and boosted), group C (primed intramuscularly and boosted orally), group D (primed and boosted orally), and group E (primed orally and boosted intramuscularly). Chickens from all immunized groups demonstrated significant increases in plasma IgG, intestinal secretory IgA levels, and antigen-specific lymphocyte proliferative response. After a virulent S. Enteritidis challenge, all immunized groups showed fewer gross lesions and decreased bacterial recovery from organs in comparison with the non-immunized control group. Among the immunized chickens, groups B and D chickens showed optimized protection, indicating that the prime-booster immunization with the ghost via intramuscular or oral route is efficient. Taken together, our results demonstrate that an antibiotic resistance gene free lysis plasmid was successfully constructed and utilized for production of safety enhanced S. Enteritidis ghost, which can be used as a safe and effective vaccine against virulent S. Enteritidis infections.

Plackett-Burman randomization method for Bacterial Ghosts preparation form E. coli JM109

Plackett-Burman randomization method is a conventional tool for variables randomization aiming at optimization. Bacterial Ghosts (BGs) preparation has been recently established using methods other than the E lysis gene. The protocol has been based mainly on using critical concentrations from chemical compounds able to convert viable cells to BGs. The Minimum Inhibition Concentration (MIC) and the Minimum Growth Concentration (MGC) were the main guide for the BGs preparation. In this study, Escherichia coli JM109 DEC has been used to produce the BGs following the original protocol. The study contained a detail protocol for BGs preparation that could be used as a guide.

Sponge-like: a new protocol for preparing bacterial ghosts

Bacterial Ghosts (BGs) received an increasing interest in the recent years for their promising medicinal and pharmaceutical applications. In this study, for the first time we introduce a new protocol for BGs production. E. coli BL21 (DE3) pLysS (Promega) was used as a model to establish a general protocol for BGs preparation. The protocol is based on using active chemical compounds in concentrations less than the Minimum Inhibition Concentration (MIC). Those chemical compounds are SDS, NaOH, and H2O2. Plackett-Burman experimental design was used to map the best conditions for BGs production. Normal and electronic microscopes were used to evaluate the BGs quality (BGQ). Spectrophotometer was used to evaluate the amount of the released protein and DNA. Agarose gel electrophoresis was used to determine the existence of any residue of DNA after each BGs preparation. Viable cells, which existed after running this protocol, were subjected to lysis by inducing the lysozyme gene carried on pLysS plasmid. This protocol is able to produce BGs that can be used in different biotechnological applications.

Bacteriophage endolysins as novel antimicrobials

Endolysins are enzymes used by bacteriophages at the end of their replication cycle to degrade the peptidoglycan of the bacterial host from within, resulting in cell lysis and release of progeny virions. Due to the absence of an outer membrane in the Gram-positive bacterial cell wall, endolysins can access the peptidoglycan and destroy these organisms when applied externally, making them interesting antimicrobial candidates, particularly in light of increasing bacterial drug resistance. This article reviews the modular structure of these enzymes, in which cell wall binding and catalytic functions are separated, as well as their mechanism of action, lytic activity and potential as antimicrobials. It particularly focuses on molecular engineering as a means of optimizing endolysins for specific applications, highlights new developments that may render these proteins active against Gram-negative and intracellular pathogens and summarizes the most recent applications of endolysins in the fields of medicine, food safety, agriculture and biotechnology.

The Bacterial Ghost platform system: production and applications

The Bacterial Ghost (BG) platform technology is an innovative system for vaccine, drug or active substance delivery and for technical applications in white biotechnology. BGs are cell envelopes derived from Gram-negative bacteria. BGs are devoid of all cytoplasmic content but have a preserved cellular morphology including all cell surface structures. Using BGs as delivery vehicles for subunit or DNA-vaccines the particle structure and surface properties of BGs are targeting the carrier itself to primary antigen-presenting cells. Furthermore, BGs exhibit intrinsic adjuvant properties and trigger an enhanced humoral and cellular immune response to the target antigen. Multiple antigens of the native BG envelope and recombinant protein or DNA antigens can be combined in a single type of BG. Antigens can be presented on the inner or outer membrane of the BG as well as in the periplasm that is sealed during BG formation. Drugs or supplements can also be loaded to the internal lumen or periplasmic space of the carrier. BGs are produced by batch fermentation with subsequent product recovery and purification via tangential flow filtration. For safety reasons all residual bacterial DNA is inactivated during the BG production process by the use of staphylococcal nuclease A and/or the treatment with β-propiolactone. After purification BGs can be stored long-term at ambient room temperature as lyophilized product. The production cycle from the inoculation of the pre-culture to the purified BG concentrate ready for lyophilization does not take longer than a day and thus meets modern criteria of rapid vaccine production rather than keeping large stocks of vaccines. The broad spectrum of possible applications in combination with the comparably low production costs make the BG platform technology a safe and sophisticated product for the targeted delivery of vaccines and active agents as well as carrier of immobilized enzymes for applications in white biotechnology.

Rectal single dose immunization of mice with Escherichia coli O157:H7 bacterial ghosts induces efficient humoral and cellular immune responses and protects against the lethal heterologous challenge

Bacterial ghosts (BGs) have been applied through oral, aerogenic, intraocular or intranasal routes for mucosal immunization using a wide range of experimental animals. All these applications required a booster after primary immunization to achieve protective immunity against the lethal challenge. Here we report for the first time that a single rectal dose of BGs produced from enterohaemorrhagic Escherichia coli (EHEC) O157:H7 fully protects mice against a 50% lethal challenge with a heterologous EHEC strain given at day 55. BGs from EHEC O157:H7 were prepared by a combination of protein E‐mediated cell lysis and expression of staphylococcal nuclease A guaranteeing the complete degradation of pathogen residual DNA. The lack of genetic material in the EHEC BGs vaccine abolished any potential hazard for horizontal gene transfer of plasmid encoded antibiotic resistance genes or pathogenic islands to the recipient's gut flora. Single rectal immunization using EHEC O157:H7 BGs without any addition of adjuvant significantly stimulated efficient humoral and cellular immune responses, and was equally protective as two immunizations, which indicates the possibility to develop a novel efficacious single dose mucosal EHEC O157:H7 BGs vaccine using a simplified immunization regimen.

Relevant uses of surface proteins--display on self-organized biological structures

Proteins are often found attached to surfaces of self‐assembling biological units such as whole microbial cells or subcellular structures, e.g. intracellular inclusions. In the last two decades surface proteins were identified that could serve as anchors for the display of foreign protein functions. Extensive protein engineering based on structure–function data enabled efficient display of technically and/or medically relevant protein functions. Small size, diversity of the anchor protein as well as support structure, genetic manipulability and controlled cultivation of phages, bacterial cells and yeasts contributed to the establishment of designed and specifically functionalized tools for applications as sensors, catalysis, biomedicine, vaccine development and library‐based screening technologies. Traditionally, phage display is employed for library screening but applications in biomedicine and vaccine development are also perceived. For some diagnostic purposes phages are even too small in size so other carrier materials where needed and gave way for cell and yeast display. Only recently, intracellular inclusions such as magnetosomes, polyhydroxyalkanoate granules and lipid bodies were conceived as stable subcellular structures enabling the display of foreign protein functions and showing potential as specific and tailor‐made devices for medical and biotechnological applications.

Generation of Vibrio anguillarum ghost by coexpression of PhiX 174 lysis E gene and staphylococcal nuclease A gene

Vibrio anguillarum ghosts (VAG) were generated, for the first time, using a conjugation vector containing a ghost bacteria inducing cassette, pRK-lambdaP(R)-cI-Elysis, in which the expression of PhiX174 lysis gene E was controlled by the P ( R )/cI regulatory system of lambda phage. By scanning electron microscopy, holes ranging 80-200 nm in diameter were observed in the VAG. To avoid the presence of bacterial genomic DNA and an antibiotic resistance gene in the final VAG product, we constructed a new dual vector, pRK-lambdaP(R)-cI-E-SNA, containing the E-mediated lysis cassette and the staphylococcal nuclease A (SNA)-mediated DNA degradation cassette, and generated safety-enhanced VAG for use as a fish vaccine.

Effective gene transfer to melanoma cells using bacterial ghosts

Bacterial ghosts (BG) are cell envelopes preparations of Gram-negative bacteria devoid of cytoplasmic content produced by controlled expression of PhiX174 plasmid-encoded lysis gene E. Eight melanoma cell lines were investigated for their capacity to bind and phagocyte BG derived from Escherichia coli NM522 and Mannheimia haemolytica A23. High capability to bind BG was observed in almost all of the analyzed cell lines, furthermore cells were able to take up BG independently of the used bacterial species. Further, transfection efficiency of BG loaded with DNA in vitro was measured. The Bowes cells exhibited a high expression level of GFP and the incubation of cells with plasmid loaded BG led up to 82% transfection efficiency.

Bacterial ghosts as adjuvant particles

The development of more advanced and effective vaccines is of great interest in modern medicine. These new-generation vaccines, based on recombinant proteins or DNA, are often less reactogenic and immunogenic than traditional vaccines. Thus, there is an urgent need for the development of new and improved adjuvants. Besides many other immunostimulatory components, the bacterial ghost (BG) system is currently under investigation as a potent vaccine delivery system with intrinsic adjuvant properties. BGs are nonliving cell envelope preparations from Gram-negative cells, devoid of cytoplasmic contents, while their cellular morphology and native surface antigenic structures remain preserved. Owing to the particulate nature of BGs and the fact that they contain many well known immune-stimulating compounds, BGs have the potential to enhance immune responses against ghost-delivered target antigens.