Mice protected by oral immunization with Lactobacillus reuteri secreting fusion protein of Escherichia coli enterotoxin subunit protein

Designer probiotics: Opening the new horizon in diagnosis and prevention of human diseases

Probiotic microorganisms have been used for therapeutic purposes for over a century, and recent advances in biotechnology and genetic engineering have opened up new possibilities for developing therapeutic approaches using indigenous probiotic microorganisms. Diseases are often related to metabolic and immunological factors, which play a critical role in their onset. With the help of advanced genetic tools, probiotics can be modified to produce or secrete important therapeutic peptides directly into mucosal sites, increasing their effectiveness. One potential approach to enhancing human health is through the use of designer probiotics, which possess immunogenic characteristics. These genetically engineered probiotics hold promise in providing novel therapeutic options. In addition to their immunogenic properties, designer probiotics can also be equipped with sensors and genetic circuits, enabling them to detect a range of diseases with remarkable precision. Such capabilities may significantly advance disease diagnosis and management. Furthermore, designer probiotics have the potential to be used in diagnostic applications, offering a less invasive and more cost-effective alternative to conventional diagnostic techniques. This review offers an overview of the different functional aspects of the designer probiotics and their effectiveness on different diseases and also, we have emphasized their limitations and future implications. A comprehensive understanding of these functional attributes may pave the way for new avenues of prevention and the development of effective therapies for a range of diseases.

Immunological effects of recombinant Lactobacillus casei expressing pilin MshB fused with cholera toxin B subunit adjuvant as an oral vaccine against Aeromonas veronii infection in crucian carp

Aeromonas veronii is a zoonotic agent capable of infecting fish and mammals, including humans, posing a serious threat to the development of aquaculture and public health safety. Currently, few effective vaccines are available through convenient routes against A. veronii infection. Herein, we developed vaccine candidates by inserting MSH type VI pili B (MshB) from A. veronii as an antigen and cholera toxin B subunit (CTB) as a molecular adjuvant into Lactobacillus casei and evaluated their immunological effect as vaccines in a crucian carp (Carassius auratus) model. The results suggested that recombinant L. casei Lc-pPG-MshB and Lc-pPG-MshB-CTB can be stably inherited for more than 50 generations. Oral administration of recombinant L. casei vaccine candidates stimulated the production of high levels of serum-specific immunoglobulin M (IgM) and increased the activity of acid phosphatase (ACP), alkaline phosphatase (AKP) superoxide dismutase (SOD), lysozyme (LZM), complement 3 (C3) and C4 in crucian carp (carassius auratus) compared to the control group (Lc-pPG612 group and PBS group) without significant changes. Moreover, the expression levels of interleukin-10 (IL-10), interleukin-1β (IL-1β), tumour necrosis factor-α (TNF-α) and transforming growth factor-β (TGF-β) genes in the gills, liver, spleen, kidney and gut of crucian carp orally immunized with recombinant L. casei were significantly upregulated compared to the control groups, indicating that recombinant L. casei induced a significant cellular immune response. In addition, viable recombinant L. casei can be detected and stably colonized in the intestine tract of crucian carp. Particularly, crucian carp immunized orally with Lc-pPG-MshB and Lc-pPG-MshB-CTB exhibited higher survival rates (48% for Lc-pPG-MshB and 60% for Lc-pPG-MshB-CTB) and significantly reduced loads of A. veronii in the major immune organs after A. veronii challenge. Our findings indicated that both recombinant L. casei strains provide favorable immune protection, with Lc-pPG-MshB-CTB in particular being more effective and promising as an ideal candidate for oral vaccination.

Characterization of a novel theta-type replicon of indigenous plasmid pTE15 from Lactobacillus reuteri N16

BACKGROUND

pTE15 is a ~ 15-kb narrow-host-range indigenous plasmid from Lactobacillus reuteri N16 that does not replicate in selected Bacillus spp., Staphylococcus spp., and other Lactobacillus spp.

METHODS

Combined deletion analysis the minireplicon essential of pTE15 with replicon-probe vector pUE80 (-) to confirmed sufficient for replication and from the ssDNA intermediate detection, plasmid amplification tested by chloramphenicol treatment, and replication origin sequence analysis to delineated the novel theta-type replication of pTE15.

RESULTS

Single-stranded intermediate of pTE15 DNA was not detected in L. reuteri, indicating that this plasmid does not replicate via a rolling circle mechanism. The replicon of pTE15 did not display the structural organization typical of rolling-circle plasmids, nor were they similar to known rolling-circle plasmids. We further provided evidence that this plasmid applied a new mode of theta-type replication mechanism: (1) the size of this plasmid was > 10-kb; (2) the minireplicon consisted of AT-rich (directed repeat, iteron) and DnaA sequences; (3) the minireplicon did not contain double-strand origin (DSO) and essential rep genes, and it also showed no single-strand origin (SSO) structure; (4) the intermediate single-stranded DNA products were not observed for pTE15 replication; (5) the minireplicon did not contain a typical essential replication protein, Rep, (6) its copy number was decreased by chloramphenicol treatment, and (7) genes in pTE15 replication region encoded truncated RepA (TRepA), RepB and RepC, which were replication-associated proteins, but they were not essential for pTE15 replication.

CONCLUSIONS

Collectively, our results strongly suggested that the indigenous plasmid pTE15 of L. reuteri N16 belongs to a new class of theta replicons.

Whole Genome Sequencing and CRISPR/Cas9 Gene Editing of Enterotoxigenic Escherichia coli BE311 for Fluorescence Labeling and Enterotoxin Analyses

Some prevention strategies, including vaccines and antibiotic alternatives, have been developed to reduce enterotoxigenic Escherichia coli proliferation in animal production. In this study, a wild-type strain of BE311 with a virulent heat-stable enterotoxin gene identical to E. coli K99 was isolated for its high potential for gene expression ability. The whole genome of E. coli BE311 was sequenced for gene analyses and editing. Subsequently, the fluorescent gene mCherry was successfully knocked into the genome of E. coli BE311 by CRISPR/Cas9. The E. coli BE311−mCherry strain was precisely quantified through the fluorescence intensity and red colony counting. The inflammatory factors in different intestinal tissues all increased significantly after an E. coli BE311−mCherry challenge in Sprague−Dawley rats (p < 0.05). The heat-stable enterotoxin gene of E. coli BE311 was knocked out, and an attenuated vaccine host E. coli BE311-STKO was constructed. Flow cytometry showed apoptotic cell numbers were lower following a challenge of IPEC-J2 cells with E. coli BE311-STKO than with E. coli BE311. Therefore, the E. coli BE311−mCherry and E. coli BE311-STKO strains that were successfully constructed based on the gene knock-in and knock-out technology could be used as ideal candidates in ETEC challenge models and for the development of attenuated vaccines.

Peptide-Based Vaccines for Tuberculosis

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis. As a result of the coronavirus disease 2019 (COVID-19) pandemic, the global TB mortality rate in 2020 is rising, making TB prevention and control more challenging. Vaccination has been considered the best approach to reduce the TB burden. Unfortunately, BCG, the only TB vaccine currently approved for use, offers some protection against childhood TB but is less effective in adults. Therefore, it is urgent to develop new TB vaccines that are more effective than BCG. Accumulating data indicated that peptides or epitopes play essential roles in bridging innate and adaptive immunity and triggering adaptive immunity. Furthermore, innovations in bioinformatics, immunoinformatics, synthetic technologies, new materials, and transgenic animal models have put wings on the research of peptide-based vaccines for TB. Hence, this review seeks to give an overview of current tools that can be used to design a peptide-based vaccine, the research status of peptide-based vaccines for TB, protein-based bacterial vaccine delivery systems, and animal models for the peptide-based vaccines. These explorations will provide approaches and strategies for developing safer and more effective peptide-based vaccines and contribute to achieving the WHO's End TB Strategy.

Prophylactic vaccine delivery systems against epidemic infectious diseases

Prophylactic vaccines have evolved from traditional whole-cell vaccines to safer subunit vaccines. However, subunit vaccines still face problems, such as poor immunogenicity and low efficiency, while traditional adjuvants are usually unable to meet specific response needs. Advanced delivery vectors are important to overcome these barriers; they have favorable safety and effectiveness, tunable properties, precise location, and immunomodulatory capabilities. Nevertheless, there has been no systematic summary of the delivery systems to cover a wide range of infectious pathogens. We herein summarized and compared the delivery systems for major or epidemic infectious diseases caused by bacteria, viruses, fungi, and parasites. We also included the newly licensed vaccines (e.g., COVID-19 vaccines) and those close to licensure. Furthermore, we highlighted advanced delivery systems with high efficiency, cross-protection, or long-term protection against epidemic pathogens, and we put forward prospects and thoughts on the development of future prophylactic vaccines.

Futuristic Non-antibiotic Therapies to Combat Antibiotic Resistance: A Review

The looming problem of resistance to antibiotics in microorganisms is a global health concern. The drug-resistant microorganisms originating from anthropogenic sources and commercial livestock farming have posed serious environmental and health challenges. Antibiotic-resistant genes constituting the environmental "resistome" get transferred to human and veterinary pathogens. Hence, deciphering the origin, mechanism and extreme of transfer of these genetic factors into pathogens is extremely important to develop not only the therapeutic interventions to curtail the infections, but also the strategies to avert the menace of microbial drug-resistance. Clinicians, researchers and policymakers should jointly come up to develop the strategies to prevent superfluous exposure of pathogens to antibiotics in non-clinical settings. This article highlights the present scenario of increasing antimicrobial-resistance in pathogenic bacteria and the clinical importance of unconventional or non-antibiotic therapies to thwart the infectious pathogenic microorganisms.

The potential of proteins, hydrolysates and peptides as growth factors forLactobacillusandBifidobacterium: current research and future perspectives

Probiotics are live microorganisms that provide health benefits to the host when consumed in adequate concentrations.

Comparison of eight Lactobacillus species for delivery of surface-displayed mycobacterial antigen

Lactobacillus spp. comprise a large group of Gram-positive lactic acid bacteria with varying physiological, ecological and immunomodulatory properties that are widely exploited by mankind, primarily in food production and as health-promoting probiotics. Recent years have shown increased interest in using lactobacilli for delivery of vaccines, mainly due to their ability to skew the immune system towards pro-inflammatory responses. We have compared the potential of eight Lactobacillus species, L. plantarum, L. brevis, L. curvatus, L. rhamnosus, L. sakei, L. gasseri, L. acidophilus and L. reuteri, as immunogenic carriers of the Ag85B-ESAT-6 antigen from Mycobacterium tuberculosis. Surface-display of the antigen was achieved in L. plantarum, L. brevis, L. gasseri and L. reuteri and these strains were further analyzed in terms of their in vitro and in vivo immunogenicity. All strains activated human dendritic cells in vitro. Immunization of mice using a homologous prime-boost regimen comprising a primary subcutaneous immunization followed by three intranasal boosters, led to slightly elevated IgG levels in serum in most strains, and, importantly, to significantly increased levels of antigen-specific mucosal IgA. Cellular immunity was assessed by studying antigen-specific T cell responses in splenocytes, which did not reveal proliferation as assessed by the expression of Ki67, but which showed clear antigen-specific IFN-γ and IL-17 responses for some of the groups. Taken together, the present results indicate that L. plantarum and L. brevis are the most promising carriers of TB vaccines.

Internalin AB-expressing recombinant Lactobacillus casei protects Caco-2 cells from Listeria monocytogenes-induced damages under simulated intestinal conditions

Background

Listeria monocytogenes is an intracellular foodborne pathogen that employs a number of strategies to survive challenging gastrointestinal conditions. It proliferates in the gut and subsequently causes listeriosis in high-risk individuals. Therefore, inhibition of its adherence to the intestinal receptors is crucial in controlling its infection. In this study, the effect of our previously developed recombinant Lactobacillus casei strain expressing invasion protein, Internalin AB of L. monocytogenes (Lbc^InlAB) on epithelial infection processes of the latter under simulated intestinal conditions was investigated.

Materials and methods

The confluent Caco-2 cell monolayer was pre-exposed to different L. casei strains at a multiplicity of exposure (MOE) of 10 for various periods before infection with L. monocytogenes at a multiplicity of infection (MOI) of 10 under simulated intestinal conditions. Subsequently, L. monocytogenes adhesion, invasion, and translocation, cytotoxicity and impact on tight junction integrity of the Caco-2 cells were analyzed.

Results

Under the simulated gastrointestinal condition, Lbc^InlAB showed a significant increase (p<0.0001) in adherence to, invasion and translocation through the Caco-2 cells when compared with the wild type strain. Although Lbc^InlAB strain exhibited enhanced inhibition of L. monocytogenes, it was not able to displace L. monocytogenes cells already attached to the monolayer. Additionally, pre-exposure to Lbc^InlAB reduced L. monocytogenes-mediated cytotoxicity and protected the tight junction barrier function.

Conclusion

The recombinant L. casei expressing InlAB shows potential for use as a prophylactic intervention strategy for targeted control of L. monocytogenes during the intestinal phase of infection.

Lactobacillus reuteri HCM2 protects mice against Enterotoxigenic Escherichia coli through modulation of gut microbiota

Enterotoxigenic Escherichia coli (ETEC) is a leading cause of infectious diarrhea in children and postweaning piglets. ETEC infection results in induced pro-inflammatory responses in intestinal epithelial cells and dysbiosis of intestinal microbiota. Here, a Lactobacillus reuteri strain, HCM2, isolated from a healthy piglet showed a high survival rate in the harsh gastrointestinal tract environment and inhibited the growth of ETEC and its adherence to intestinal epithelial cells. Pre-supplementation with L. reuteri HCM2 for 14 days reduced the ETEC load in the jejunum of ETEC-infected mice and prevented the disruption of intestinal morphology by ETEC. The colonic microbiota of mice with or without HCM2 pre-supplementation were analyzed, and this analysis revealed that HCM2 could prevent dysbiosis caused by ETEC infection by stabilizing the relative abundance of dominant bacteria. These results indicate that L. reuteri HCM2 has the potential to attenuate the effect of ETEC on the colonic microbiota in infected mice.

Vaccines as alternatives to antibiotics for food producing animals. Part 2: new approaches and potential solutions

Vaccines and other alternative products are central to the future success of animal agriculture because they can help minimize the need for antibiotics by preventing and controlling infectious diseases in animal populations. To assess scientific advancements related to alternatives to antibiotics and provide actionable strategies to support their development, the United States Department of Agriculture, with support from the World Organisation for Animal Health, organized the second International Symposium on Alternatives to Antibiotics. It focused on six key areas: vaccines; microbial-derived products; non-nutritive phytochemicals; immune-related products; chemicals, enzymes, and innovative drugs; and regulatory pathways to enable the development and licensure of alternatives to antibiotics. This article, the second part in a two-part series, highlights new approaches and potential solutions for the development of vaccines as alternatives to antibiotics in food producing animals; opportunities, challenges and needs for the development of such vaccines are discussed in the first part of this series. As discussed in part 1 of this manuscript, many current vaccines fall short of ideal vaccines in one or more respects. Promising breakthroughs to overcome these limitations include new biotechnology techniques, new oral vaccine approaches, novel adjuvants, new delivery strategies based on bacterial spores, and live recombinant vectors; they also include new vaccination strategies in-ovo, and strategies that simultaneously protect against multiple pathogens. However, translating this research into commercial vaccines that effectively reduce the need for antibiotics will require close collaboration among stakeholders, for instance through public–private partnerships. Targeted research and development investments and concerted efforts by all affected are needed to realize the potential of vaccines to improve animal health, safeguard agricultural productivity, and reduce antibiotic consumption and resulting resistance risks.

Evaluation of recombinant Salmonella vaccines to provide cross-serovar and cross-serogroup protection

Historically, Salmonella vaccines have been either live attenuated or killed bacterin vaccines that fail to offer cross-serogroup protection, which limits risk mitigation and protection of consumers. Subunit recombinant vaccines which possess highly conserved antigens offer potential to provide cross-serogroup protection, and the ability to express immune-enhancing molecules that promote recognition by the immune system. Six Salmonella subunit vaccine candidates were developed in either attenuated S. Enteritidis (SE) or S. Typhimurium (ST) that cell-surface express antigenic epitopes of high mobility group box 1 immune-enhancing sequence (H), peptidoglycan associated lipoprotein (P), and Omp18 protein Cj0113 (C) in different pattern arrangements for evaluation against S. Heidelberg (SH) challenge in broilers. In exp. 1, chicks were orally vaccinated with SE-CPH, SE-HCP, SE-CHP, ST-CPH, ST-HCP, or ST-CHP at 1 × 107 cfu/chick, or saline on d 1 and d 14. On d 17 all birds were challenged with 6 × 106 cfu/chick SH, and ceca collected on d 23 and d 28. On d 23 only SE-CPH reduced (P < 0.05) SH recovery at 0.34 ± 0.23 log10 cfu when compared to control at 1.19 ± 0.26 log10 cfu. On d 28, SE-CPH and ST-HCP reduced SH recovery at 0.40 ± 0.40 and 0.51 ± 0.26 log10 cfu, respectively in comparison to control at 1.36 ± 0.23 log10 cfu. For exp. 2, chicks were orally vaccinated with 1 × 108 cfu/chick SE-CPH, SE-HCP, SE-CHP or saline on d 1. At d 7 all chicks were orally challenged with 7 × 106 cfu/chick SH and ceca collected on d 28 and d 35. SE-CPH reduced (P < 0.05) SH recovery on d 28 when compared to control (6.16 ± 0.13 vs. 4.71 ± 0.55 log10 cfu). In exp 3, chicks were vaccinated by spray in a commercial vaccination cabinet with SE-CPH vaccination, 1.6 × 107 cfu/chick, or saline. Birds were challenged on d 14 with 3 × 107 cfu/chick SH and ceca collected on d 18 and d 25. SE-CPH reduced SH recovery (P < 0.05) on d 18, 2.75 ± 0.05 log10 cfu, and d 25, 1.89 ± 0.43 log10 cfu, as compared to control chickens at 5.6 ± 0.37 (d 18) and 3.98 ± 0.5 log10 cfu (d 25). The results of these experiments suggest that cross-serogroup protection is possible using these SE and ST-vectored subunit vaccines.

Lactobacillus Mucosal Vaccine Vectors: Immune Responses against Bacterial and Viral Antigens

Lactic acid bacteria (LAB) have been utilized since the 1990s for therapeutic heterologous gene expression. The ability of LAB to elicit an immune response against expressed foreign antigens has led to their exploration as potential mucosal vaccine candidates. LAB vaccine vectors offer many attractive advantages: simple, noninvasive administration (usually oral or intranasal), the acceptance and stability of genetic modifications, relatively low cost, and the highest level of safety possible. Experimentation using LAB of the genus Lactobacillus has become popular in recent years due to their ability to elicit strong systemic and mucosal immune responses. This article reviews Lactobacillus vaccine constructs, including Lactobacillus species, antigen expression, model organisms, and in vivo immune responses, with a primary focus on viral and bacterial antigens.

Expression of the alpha toxin of Clostridium perfringens in Lactobacillus casei genome and evaluation of its immune effects in mice

We previously developed a stable and marker-free Lactobacillus casei strain (PPαT Δupp) that contained a chromosomally integrated expression cassette (PPαT) that enabled the surface expression of the Clostridium perfringens alpha toxin. To measure immune responses against the alpha toxin, specific-pathogen-free BALB/c mice were inoculated with L. casei PPαT Δupp by oral gavage. Then, specific immunoglobulin A (IgA) and immunoglobulin G (IgG) antibodies and cytokines were measured by enzyme-linked immunosorbent assay (ELISA) and flow cytometry (FCM). The results showed that alpha toxin-specific IgA and IgG antibodies and cytokines were markedly increased following immunization. Natural alpha toxin challenge and neutralization tests were performed. The results showed that immunized mice can fully resist 1.5 minimum lethal doses of toxin. These results indicated that the immunized mice can produce not only humoral immunity, but also cellular immunity. These results provide a new pathway for the development of a safe, effective, and food-grade vaccine.

Engineered Probiotics: Applications and Biological Containment

Bioengineered probiotics represent the next generation of whole cell-mediated biotherapeutics. Advances in synthetic biology, genome engineering, and DNA sequencing and synthesis have enabled scientists to design and develop probiotics with increased stress tolerance and the ability to target specific pathogens and their associated toxins, as well as to mediate targeted delivery of vaccines, drugs, and immunomodulators directly to host cells. Herein, we review the most significant advances in the development of this field. We discuss the critical issue of biological containment and consider the role of synthetic biology in the design and construction of the probiotics of the future.

Expression and Purification of the Uropathogenic Escherichia coli PapG Protein and its Surface Absorption on Lactobacillus reuteri: Implications for Surface Display System Vaccines

Background:

Uropathogenic Escherichia coli (UPEC) is one of the most common bacteria that can cause urinary tract infections (UTIs). Unfortunately, no human vaccine against UTIs has been developed. Therefore, it is necessary to develop an efficient and safe vaccine that is able to induce mucosal and systemic immune responses. The use of lactic acid bacteria as a delivery system is a promising method to induce the immune system.

Objectives:

The aim of this study was to establish Lactobacillus reuteri harboring the E. coli PapG antigen on its surface.

Materials and Methods:

In this study, the gene encoding PapG was fused to the AcmA gene (which encodes an anchor protein in Lactobacillus) and cloned into the pEX A vector. The PapG.AcmA fusion gene was digested with BamHI and NdeI and sub-cloned into the pET21a expression vector at the digestion sites. Subsequently, the recombinant plasmids (pET21a-PapG.AcmA and pET21a-PapG) were transformed into the E. coli Origami strain using the calcium chloride method and the fusion protein was expressed under 1 mM IPTG induction. The expression of the fusion protein was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western blotting. Purification of the PapG and PapG.AcmA proteins was carried out using a Ni-NTA column, and surface adsorption was estimated on Lactobacillus. Finally, surface localization of the fusion protein was verified by an enzyme-linked immunosorbent assay (ELISA).

Results:

The PapG.AcmA fusion was successfully sub-cloned in the pET21a expression vector. The expression of PapG and PapG.AcmA proteins in the E. coli Origami strain was indicated as protein bands in SDS-PAGE and confirmed by western blotting. In addition, the fusion protein was displayed on the surface of L. reuteri.

Conclusions:

In conclusion, we developed a method to express the PapG.AcmA protein on the surface of Lactobacillus. This is the first report on the successful application of lactic acid bacteria displaying the PapG.AcmA fusion protein. It will be interesting to determine the immune responses against the PapG protein in near future using this surface display strategy.

Antigen Delivery System II

This chapter reviews papers mostly written since 2005 that report results using live attenuated bacterial vectors to deliver after administration through mucosal surfaces, protective antigens, and DNA vaccines, encoding protective antigens to induce immune responses and/or protective immunity to pathogens that colonize on or invade through mucosal surfaces. Papers that report use of such vaccine vector systems for parenteral vaccination or to deal with nonmucosal pathogens or do not address induction of mucosal antibody and/or cellular immune responses are not reviewed.

Characterization of two truncated forms of xylanase recombinantly expressed by Lactobacillus reuteri with an introduced rumen fungal xylanase gene

The xylanase R8 gene (xynR8) from uncultured rumen fungi was cloned and successfully expressed in Lactobacillus reuteri. A xylanase activity of 132.1 U/mL was found in the broth of L. reuteri R8, the transformant containing pNZ3004 vector with xynR8 gene insertion. Two distinct forms of recombinant xylanase with different hydrophobicities and molecular weights were found in the broth after purification. According to the results of Western blotting, only the T7-tag, fused in the N-terminus of XynR8, could be bound to the expressed proteins, which indicated that the C-terminus of XynR8 had been truncated. These results, combined with tryptic digestion and mass spectrometry analyses, allow us to attribute the two xylanase forms to an optional cleavage of C-terminal sequences, and XynR8A, a 13 amino acid residues truncated form, and XynR8B, a 22 amino acid residues truncated form, were the main products in the extracellular fraction of L. reuteri R8. The specific activities of XynR8A and R8B were 1028 and 395 U/mg protein. Both forms of recombinant xylanase displayed a typical endoxylanase activity when they were reacted with xylan, but XynR8A demonstrated a better specific activity, catalytic efficiency and thermostability than XynR8B according to the results of enzyme characterization. These changes in enzyme properties were highly possibly caused by the present of the β-sheet in the C-terminal undeleted fragment of XynR8A. This study demonstrates that modified forms with different enzyme properties could be produced when a gene was recombinantly expressed by a L. reuteri transformant.

Bioengineered probiotics, a strategic approach to control enteric infections

Enteric infections account for high morbidity and mortality and are considered to be the fifth leading cause of death at all ages worldwide. Seventy percent of all enteric infections are foodborne. Thus significant efforts have been directed toward the detection, control and prevention of foodborne diseases. Many antimicrobials including antibiotics have been used for their control and prevention. However, probiotics offer a potential alternative intervention strategy owing to their general health beneficial properties and inhibitory effects against foodborne pathogens. Often, antimicrobial probiotic action is non-specific and non-discriminatory or may be ineffective. In such cases, bioengineered probiotics expressing foreign gene products to achieve specific function is highly desirable. In this review we summarize the strategic development of recombinant bioengineered probiotics to control enteric infections, and to examine how scientific advancements in the human microbiome and their immunomodulatory effects help develop such novel and safe bioengineered probiotics.

Recent advances in understanding enteric pathogenic Escherichia coli

Although Escherichia coli can be an innocuous resident of the gastrointestinal tract, it also has the pathogenic capacity to cause significant diarrheal and extraintestinal diseases. Pathogenic variants of E. coli (pathovars or pathotypes) cause much morbidity and mortality worldwide. Consequently, pathogenic E. coli is widely studied in humans, animals, food, and the environment. While there are many common features that these pathotypes employ to colonize the intestinal mucosa and cause disease, the course, onset, and complications vary significantly. Outbreaks are common in developed and developing countries, and they sometimes have fatal consequences. Many of these pathotypes are a major public health concern as they have low infectious doses and are transmitted through ubiquitous mediums, including food and water. The seriousness of pathogenic E. coli is exemplified by dedicated national and international surveillance programs that monitor and track outbreaks; unfortunately, this surveillance is often lacking in developing countries. While not all pathotypes carry the same public health profile, they all carry an enormous potential to cause disease and continue to present challenges to human health. This comprehensive review highlights recent advances in our understanding of the intestinal pathotypes of E. coli.

Immune responses of chickens inoculated with recombinant Lactobacillus expressing the haemagglutinin of the avian influenza virus

AIMS

To develop a safe, effective and convenient vaccine for the prevention of highly pathogenic avian influenza (HPAI), we have successfully constructed a recombinant lactobacillus (LDL17-pH) that expresses the foreign HPAI protein, haemagglutinin 1 (HA1 ).

METHODS AND RESULTS

The mucosal and systemic immune responses that are triggered by LDL17-pH following the oral administration to 10-day-old chickens were evaluated. The results showed that LDL17-pH could significantly increase the specific anti-HA1 IgA antibody level in the mucosa and the anti-HA1 IgG level in sera. Tissues were isolated from trachea and Peyer's patches(PPs)and caecal tonsils of chickens, and gene expression was analysed via real-time quantitative PCR.

CONCLUSIONS

The results showed that LDL17-pH could significantly induce the specific anti-HA1 IgA antibody level in the trachea and intestine and the specific anti-HA1 IgG antibody level in the serum (P < 0·05). Additionally, LDL17-pH was in the capacity to induce the expression of cytokines IFN-γ, TLR-2 and AvBD-9 in the PPs and caecal tonsils. Most importantly, the chickens that were immunized with LDL17-pH were protected against lethal challenge of the H5N1 virus to some extent.

SIGNIFICANCE AND IMPACT OF THE STUDY

Therefore, LDL17-pH could be a promising oral vaccine candidate against HPAI.

Class A β-lactamases as versatile scaffolds to create hybrid enzymes: applications from basic research to medicine

Designing hybrid proteins is a major aspect of protein engineering and covers a very wide range of applications from basic research to medical applications. This review focuses on the use of class A β-lactamases as versatile scaffolds to design hybrid enzymes (referred to as β-lactamase hybrid proteins, BHPs) in which an exogenous peptide, protein or fragment thereof is inserted at various permissive positions. We discuss how BHPs can be specifically designed to create bifunctional proteins, to produce and to characterize proteins that are otherwise difficult to express, to determine the epitope of specific antibodies, to generate antibodies against nonimmunogenic epitopes, and to better understand the structure/function relationship of proteins.

Codon optimisation to improve expression of a Mycobacterium avium ssp. paratuberculosis-specific membrane-associated antigen by Lactobacillus salivarius

Subunit and DNA-based vaccines against Mycobacterium avium ssp. paratuberculosis (MAP) attempt to overcome inherent issues associated with whole-cell formulations. However, these vaccines can be hampered by poor expression of recombinant antigens from a number of disparate hosts. The high G+C content of MAP invariably leads to a codon bias throughout gene expression. To investigate if the codon bias affects recombinant MAP antigen expression, the open reading frame of a MAP-specific antigen MptD (MAP3733c) was codon optimised for expression against a Lactobacillus salivarius host. Of the total 209 codons which constitute MAP3733c, 172 were modified resulting in a reduced G+C content from 61% for the native gene to 32.7% for the modified form. Both genes were placed under the transcriptional control of the PnisA promoter; allowing controlled heterologous expression in L. salivarius. Expression was monitored using fluorescence microscopy and microplate fluorometry via GFP tags translationally fused to the C-termini of the two MptD genes. A > 37-fold increase in expression was observed for the codon-optimised MAP3733synth variant over the native gene. Due to the low cost and improved expression achieved, codon optimisation significantly improves the potential of L. salivarius as an oral vaccine stratagem against Johne's disease.

Oral immunization with recombinant Lactococcus lactis expressing the hemagglutinin of the avian influenza virus induces mucosal and systemic immune responses

AIMS

The aim of the study in this article is to explore a safe, convenient and effective oral mucosal vaccine candidate against highly pathogenic avian influenza.

MATERIALS & METHODS

We have constructed an oral mucosal vaccine, LL36EH, by use of the genetically stable θ-replicating vector pMG36E, which expressed the fusion protein hemagglutinin 1 (HA(1)) in a live carrier, Lactococcus lactis MG1363. LL36EH was administered orally to mice three times at 2-week intervals. The specific serum IgG and mucosal IgA antibodies were detected and evaluated at different time points after immunization.

RESULTS

The results showed that LL36EH could significantly induce specific anti-HA(1) IgA antibody in the intestine and specific anti-HA(1) IgG antibody in the serum (p < 0.05). Additionally, when the splenic lymphocytes isolated from immunized mice were stimulated by HA(1) antigen in vitro, splenic lymphocyte proliferative reaction and secretions of the cytokines IFN-γ and IL-4 were also significantly increased. Most importantly, the mice that were immunized with LL36EH were protected to some extent against lethal challenge of the H5N1 virus.

CONCLUSION

LL36EH triggered the anti-HA(1)-specific humoral and cellular immune responses and protective immunity. Therefore, oral immunization with LL36EH could be a valuable strategy against highly pathogenic avian influenza for humans and animals.

Development of vaccine delivery vehicles based on lactic acid bacteria

Live recombinant bacteria represent attractive antigen delivery systems able to induce both mucosal and systemic immune responses against heterologous antigens. The first live recombinant bacterial vectors developed were derived from attenuated pathogenic microorganisms. In addition to the difficulties often encountered in the construction of stable attenuated mutants of pathogenic organisms, attenuated pathogens may retain a residual virulence level that renders them unsuitable for the vaccination of partially immunocompetent individuals such as infants, the elderly or immunocompromised patients. As an alternative to this strategy, non-pathogenic food-grade lactic acid bacteria (LAB) maybe used as live antigen carriers. This article reviews LAB vaccines constructed using antigens other than tetanus toxin fragment C, against bacterial, viral, and parasitic infective agents, for which protection studies have been performed. The antigens utilized for the development of LAB vaccines are briefly described, along with the efficiency of these systems in protection studies. Moreover, the key factors affecting the performance of these systems are highlighted.

Mucosal and systemic immune responses induced by recombinant Lactobacillus spp. expressing the hemagglutinin of the avian influenza virus H5N1

To develop a safe, effective, and convenient vaccine for the prevention of highly pathogenic avian influenza (HPAI), we have successfully constructed two recombinant lactobacillus strains (LA4356-pH and DLD17-pH) that express the foreign HPAI virus protein hemagglutinin 1 (HA(1)). The mucosal and systemic immune responses triggered by these two recombinant lactobacilli following oral administration to BALB/c mice were evaluated. The results showed that both LA4356-pH and DLD17-pH could significantly increase the specific anti-HA(1) IgA antibody level in the mucosa and the anti-HA(1) IgG level in serum, as well as stimulating the splenic lymphocyte proliferative reaction through increased expression of interleukin-4 (IL-4). Compared with LA4356-pH, DLD17-pH was more effective at inducing systemic and mucosal immune responses, with higher anti-HA(1)-specific IgA and IgG levels. Therefore, DLD17-pH could be a promising oral vaccine candidate against HPAI.

Platform technology to deliver prophylactic molecules orally: an example using the Class A select agent Yersinia pestis

Consumed for centuries, lactic acid bacteria are excellent candidates for the development of safe mucosal delivery vehicles for prophylactic and therapeutic molecules. We have recently reported that the immune response to an effective OspA-expressing L. plantarum vaccine for Lyme disease is modulated by the lipid modification of the antigen. In this study, we investigated if this technology can be applied to developing vaccines for other diseases by focusing on the Class A select agent, Yersinia pestis. We used a number of biochemistry and immunology techniques to determine the localization of the immunogen in our delivery vehicle and to evaluate the mucosal as well as the systemic immune response to the immunogen. We found that only LcrV cloned downstream of the signal sequence of B. burgdorferi OspA ((ss)LcrV), but not wildtype LcrV (LcrV), is localized to the desired peptidoglycan layer of the delivery vehicle. In addition, only mice that received L. plantarum expressing (ss)LcrV produced significant titers of IgG antibody as well as IgA in distant mucosal sites such as lungs and vagina. Furthermore, only L. plantarum expressing (ss)LcrV induced significant amounts of pro-inflammatory cytokines TNFα, IL-12, IFNγ and IL-6 as well as anti-inflammatory IL-10 in human peripheral blood mononuclear cells derived dendritic cells, suggesting that the mechanism by which LcrV-expressing L. plantarum stimulates the immune response involves polarization to Th1 mediated immunity with some involvement of Th2. The study reported here proves that this system is a platform technology to develop oral vaccines for multiple diseases.

Immune response to Lactobacillus plantarum expressing Borrelia burgdorferi OspA is modulated by the lipid modification of the antigen

BACKGROUND

Over the past decade there has been increasing interest in the use of lactic acid bacteria as mucosal delivery vehicles for vaccine antigens, microbicides and therapeutics. We investigated the mechanism by which a mucosal vaccine based in recombinant lactic acid bacteria breaks the immunological tolerance of the gut in order to elicit a protective immune response.

METHODOLOGY/PRINCIPAL FINDINGS

We analyzed how the lipid modification of OspA affects the localization of the antigen in our delivery vehicle using a number of biochemistry techniques. Furthermore, we examined how OspA-expressing L. plantarum breaks the oral tolerance of the gut by stimulating human intestinal epithelial cells, peripheral blood mononuclear cells and monocyte derived dendritic cells and measuring cytokine production. We show that the leader peptide of OspA targets the protein to the cell envelope of L. plantarum, and it is responsible for protein export across the membrane. Mutation of the lipidation site in OspA redirects protein localization within the cell envelope. Further, we show that lipidated-OspA-expressing L. plantarum does not induce secretion of the pro-inflammatory cytokine IL-8 by intestinal epithelial cells. In addition, it breaks oral tolerance of the gut via Th1/Th2 cell mediated immunity, as shown by the production of pro- and anti-inflammatory cytokines by human dendritic cells, and by the production of IgG2a and IgG1 antibodies, respectively.

CONCLUSIONS/SIGNIFICANCE

Lipid modification of OspA expressed in L. plantarum modulates the immune response to this antigen through a Th1/Th2 immune response.

Comparison of expression vectors in Lactobacillus reuteri strains

The synthesis of heterologous proteins in lactobacilli is strongly influenced by the promoter selected for the expression. In addition, the activity of the promoters themselves may vary among different bacterial hosts. Three different promoters were investigated for their capability to drive enhanced green fluorescent protein (EGFP) expression in Lactococcus lactis spp. cremoris MG1363, in Lactobacillus reuteri DSM 20016(T) and in five L. reuteri strains isolated from chicken crops. The promoters of the Lactobacillus acidophilus surface layer protein gene (slp), L. acidophilus lactate dehydrogenase gene (ldhL) and enterococcal rRNA adenine N-6-methyltransferase gene (ermB) were fused to the coding sequence of EGFP and inserted into the backbone of the pTRKH3 shuttle vector (pTRKH3-slpGFP, pTRKH3-ldhGFP, pTRKH3-ermGFP). Besides conventional analytical methods, a new quick fluorimetric approach was set up to quantify the EGFP fluorescence in transformed clones using the Qubit() fluorometer. ermB proved to be the most effective promoter in L. reuteri isolates, producing 3.90 x 10(-7) g of fluorescent EGFP (mL OD(stationary culture))(-1). Under the same conditions, the ldhL promoter produced 2.66 x 10(-7) g of fluorescent EGFP (mL OD(stationary culture))(-1). Even though the slp promoter was efficient in L. lactis spp. cremoris MG1363, it was nearly inactive both in L. reuteri DSM 20016(T) and in L. reuteri isolates.

Heat-stable enterotoxin of enterotoxigenic Escherichia coli as a vaccine target

Enterotoxigenic Escherichia coli (ETEC) is responsible for 280 million to 400 million episodes of diarrhea and about 380,000 deaths annually. Epidemiological data suggest that ETEC strains which secrete heat-stable toxin (ST), alone or in combination with heat-labile toxin (LT), induce the most severe disease among children in developing countries. This makes ST an attractive target for inclusion in an ETEC vaccine. ST is released upon colonization of the small intestine and activates the guanylate cyclase C receptor, causing profuse diarrhea. To generate a successful toxoid, ST must be made immunogenic and nontoxic. Due to its small size, ST is nonimmunogenic in its natural form but becomes immunogenic when coupled to an appropriate large-molecular-weight carrier. This has been successfully achieved with several carriers, using either chemical conjugation or recombinant fusion techniques. Coupling of ST to a carrier may reduce toxicity, but further reduction by mutagenesis is desired to obtain a safe vaccine. More than 30 ST mutants with effects on toxicity have been reported. Some of these mutants, however, have lost the ability to elicit neutralizing immune responses to the native toxin. Due to the small size of ST, separating toxicity from antigenicity is a particular challenge that must be met. Another obstacle to vaccine development is possible cross-reactivity between anti-ST antibodies and the endogenous ligands guanylin and uroguanylin, caused by structural similarity to ST. Here we review the molecular and biological properties of ST and discuss strategies for developing an ETEC vaccine that incorporates immunogenic and nontoxic derivatives of the ST toxin.

Induction of immune responses in mice after oral immunization with recombinant Lactobacillus casei strains expressing enterotoxigenic Escherichia coli F41 fimbrial protein

In an effort to develop a safe and effective vaccine for the prevention of enterotoxigenic Escherichia coli (ETEC) F41 infections, we have developed a surface antigen display system using poly-gamma-glutamate synthetase A (PgsA) as an anchoring matrix. The recombinant fusion proteins comprised of PgsA and fimbrial protein of F41 were stably expressed in Lactobacillus casei 525. Surface localization of the fusion protein was verified by immunoblotting, immunofluorescence microscopy, and flow cytometry. Oral inoculation of recombinant L. casei 525 into specific-pathogen-free BALB/c mice resulted in significant mucosal immunoglobulin A (IgA) titers that remained elevated for >16 weeks. High levels of IgG responses in sera specific for F41 fimbriae were also induced, with prominent IgG1 titers as well as IgG2a and IgG2b titers. The helper T-cell (Th) response was Th2-cell dominant, as evidenced by increased mucosal and systemic interleukin-4-producing T cells and a concomitant elevation of serum IgG1 antibody responses. More than 80% of the mice were protected against challenge with a 2 x 10(4)-fold 50% lethal dose of standard-type F41 (C83919). The induced antibodies were important for eliciting a protective immune response against F41 infection. These results indicated that the use of recombinant L. casei 525 could be a valuable strategy for future vaccine development for ETEC.

Characterization of the cattle serum antibody responses against TEM beta-lactamase and the nonimmunogenic Escherichia coli heat-stable enterotoxin (STaI)

In order to test the use of a subunit recombinant vaccine for its capacity to induce antibodies against the nonimmunogenic heat-stable enterotoxin STa from Escherichia coli and the TEM-1 beta-lactamase, cattle were immunized with a hybrid protein created by insertion of the STa sequence at position 197 of the TEM-1 beta-lactamase. Specific anti-STa IgG and IgG1 antibodies were detected at low levels, while no IgG2 antibodies were detected. In contrast, high levels of the different anti-TEM IgG subtypes were detected in cattle sera. In addition, beta-lactamase activity was inhibited by the sera. The presence of antibodies against STa and TEM-1 beta-lactamase was assessed in sera from 366 cattle taken from the field. No significant level of IgGs against the toxin or the TEM-1 was detected. A comparison of the antibody level between the immunized and the nonimmunized animals clearly demonstrated that STa was not able to induce a significant level of antibodies in the vaccinated animals. In contrast, a strong antibody response against TEM-1 beta-lactamase was demonstrated.

Immunization of mice with Lactobacillus casei expressing intimin fragments produces antibodies able to inhibit the adhesion of enteropathogenic Escherichia coli to cultivated epithelial cells

Enteropathogenic Escherichia coli (EPEC) are frequently isolated as a cause of infantile diarrhea in developing countries. Its pathogenicity is distinguished by histopathological alterations at the site of infection, known as attaching and effacing (A/E) lesions, in which bacterial virulence factors and host proteins participate. Intimin, a bacterial adhesin expressed by all EPEC described to date, is responsible for the intimate adherence of the bacteria to host cells and is essential for the formation of A/E lesions. Mucosal vaccination may represent an efficacious intervention to prevent EPEC infection and lower morbidity and mortality rates. Strategies for mucosal vaccinations that use lactic acid bacteria for the delivery of heterologous antigens rely on their safety profile and ability to stimulate the immune system. In the present work, we have constructed Lactobacillus casei strains expressing different fragments of intimin beta, a subtype that is frequently expressed by EPEC strains. Mucosal immunization of mice with L. casei expressing intimin fragments induced specific systemic and mucosal antibodies. These antibodies were able to recognize native intimin on the surface of EPEC and to inhibit in vitro EPEC binding to epithelial cells.

Oral immunization with recombinant lactobacillus plantarum induces a protective immune response in mice with Lyme disease

Mucosal immunization is advantageous over other routes of antigen delivery because it can induce both mucosal and systemic immune responses. Our goal was to develop a mucosal delivery vehicle based on bacteria generally regarded as safe, such as Lactobacillus spp. In this study, we used the Lyme disease mouse model as a proof of concept. We demonstrate that an oral vaccine based on live recombinant Lactobacillus plantarum protects mice from tick-transmitted Borrelia burgdorferi infection. Our method of expressing vaccine antigens in L. plantarum induces both systemic and mucosal immunity after oral administration. This platform technology can be applied to design oral vaccine delivery vehicles against several microbial pathogens.