Trivalent outer membrane vesicles-based combination vaccine candidate induces protective immunity against Campylobacter and invasive non-typhoidal Salmonella in adult mice.

Campylobacter and invasive non-typhoidal Salmonella (iNTS) are among the most common causative agents of gastroenteritis worldwide. As of now, no single combination licensed vaccine is available for public health use against both iNTS and Campylobacter species. Outer-membrane vesicles (OMVs) are nanoscale proteoliposomes released from the surface of gram-negative bacteria during log phase and harbor a variety of immunogenic proteins. Based on epidemiology of infections, we formulated a novel trivalent outer membrane vesicles (TOMVs)-based vaccine candidate against Campylobacter jejuni (CJ), Salmonella Typhimurium (ST) and Salmonella Enteritidis (SE). Isolated OMVs from CJ, ST and SE were combined in equal ratios for formulation of TOMVs and 5 µg of the developed vaccine candidate was used for intraperitoneal immunization of adult BALB/c mice. Immunization with TOMVs significantly activated both the humoral and cellular arm of adaptive immune response. Robust bactericidal effect was elicited by TOMVs immunized adult mice sera. TOMVs immunization induced long-term protective efficacy against CJ, ST and SE infections in mice. The study illustrates the ability of TOMVs-based combination immunogen in eliciting broad-spectrum protective immunity against prevalent Campylobacter and iNTS pathogens. According to the findings, TOMVs can work as a potent combination-based acellular vaccine candidate for amelioration of Campylobacter and iNTS-mediated gastroenteritis.

Development of a nano-emulsion based multivalent protein subunit vaccine against Pseudomonas aeruginosa.

Pseudomonas aeruginosa (Pa) is an opportunistic bacterial pathogen responsible for severe hospital acquired infections in immunocompromised and elderly individuals. Emergence of increasingly drug resistant strains and the absence of a broad-spectrum prophylactic vaccine against both T3SA+ (type III secretion apparatus) and ExlA+/T3SA- Pa strains worsen the situation in a post-pandemic world. Thus, we formulated a candidate subunit vaccine (called ExlA/L-PaF/BECC/ME) against both Pa types. This bivalent vaccine was generated by combining the C-terminal active moiety of exolysin A (ExlA) produced by non-T3SA Pa strains with our T3SA-based vaccine platform, L-PaF, in an oil-in-water emulsion. The ExlA/L-PaF in ME (MedImmune emulsion) was then mixed with BECC438b, an engineered lipid A analogue and a TLR4 agonist. This formulation was administered intranasally (IN) to young and elderly mice to determine its potency across a diverse age-range. The elderly mice were used to mimic the infection seen in elderly humans, who are more susceptible to serious Pa disease compared to their young adult counterparts. After Pa infection, mice immunized with ExlA/L-PaF/BECC/ME displayed a T cell-mediated adaptive response while PBS-vaccinated mice experienced a rapid onset inflammatory response. Important genes and pathways were observed, which give rise to an anti-Pa immune response. Thus, this vaccine has the potential to protect aged individuals in our population from serious Pa infection.

Pentavalent outer membrane vesicles immunized mice sera confers passive protection against five prevalent pathotypes of diarrhoeagenic Escherichia coli in neonatal mice.

Diarrhoeagenic Escherichia coli (DEC) pathotypes are one of the major causative agents of diarrhoea induced childhood morbidity and mortality in developing countries. Licensed vaccines providing broad spectrum protection against DEC mediated infections are not available. Outer membrane vesicles (OMVs) are microvesicles released by gram-negative bacteria during the growth phase and contain multiple immunogenic proteins. Based on prevalence of infections, we have formulated a pentavalent outer-membrane vesicles (POMVs) based immunogen targeting five main pathotypes of DEC responsible for diarrhoeal diseases. Following isolation, OMVs from five DEC pathotypes were mixed in equal proportions to formulate POMVs and 10 µg of the immunogen was intraperitoneally administered to adult BALB/c mice. Three doses of POMVs induced significant humoral immune response against whole cell lysates (WCLs), outer membrane proteins (OMPs) and lipopolysaccharides (LPS) isolated from DEC pathotypes along with significant induction of cellular immune response in adult mice. Passive transfer of POMVs immunized adult mice sera protected neonatal mice significantly against DEC infections. Overall, this study finds POMVs to be immunogenic in conferring broad-spectrum passive protection to neonatal mice against five main DEC pathotypes. Altogether, these findings suggest that POMVs can be used as a potent vaccine candidate to ameliorate the DEC-mediated health burden.

Bacterial ghost cell based bivalent candidate vaccine against Salmonella Typhi and Salmonella Paratyphi A: A prophylactic study in BALB/c mice.

Typhoid and emerging paratyphoid fever are a severe enteric disease worldwide with high morbidity and mortality. Licensed typhoid vaccines are in the market, but no paratyphoid vaccine is currently available. In the present study we developed a bivalent vaccine against Salmonella Typhi and Paratyphi A using a bacterial ghost platform. Bacterial ghost cells (BGs) are bacteria-derived cell membranes without cytoplasmic contents that retain their cellular morphology, including all cell surface features. Furthermore, BGs have inherent adjuvant properties that promote an enhanced humoral and cellular immune reaction to the target antigen. Sodium hydroxide was used to prepare ghost cells of Salmonella Typhi and Paratyphi A. The bacterial ghost cells were characterised using electron microscopy. Then BALB/c mice were immunized three times (0th, 14th and 28th day) with the bivalent typhoidal bacterial ghost cells. Haematological study of adult mice throughout immunization period reflected that the immunogen was safe to administer and does not affect the animals' health. After complete immunization, we found significant serum antibody titter against whole cell lysate, outer membrane protein and lipopolysaccharide of both bacteria, and cell-mediated immunity was observed in an ex-vivo experiment. CD4+, CD8a+ and CD19+ splenic cell populations were increased in immunized animals. Bivalent Typhoidal ghost cell immunized mice showed better survival, less bacterial colonization in systemic organs, and less inflammation and/or destruction of tissue in histopathological analysis than non-immunized control mice.Serum antibodies of immunized animals can significantly inhibit bacterial motility and mucin penetration ability with better killing properties against Salmonella Typhi and Paratyphi A. Furthermore, significant passive protection was observed through the adoptive transfer of serum antibody and lymphocytes of immunized animals to naïve animals after bacterial infection. In summary, Bivalent Typhoidal Bacterial Ghost cells (BTBGs) enhances immunogenic properties and serves as a safe and effective prevention strategy against Salmonella Typhi and Paratyphi A.

A tetravalent Shigella outer membrane vesicles based candidate vaccine offered cross-protection against all the serogroups of Shigella in adult mice.

In today's world and mostly in low and middle income countries, Shigella flexneri and Shigella sonnei remains the major causative agent of clinical bacillary dysentery. Based on contemporary epidemiology, a tetravalent Outer Membrane Vesicle (OMVs) based immunogen was formulated using the most commonly circulating Shigella strains, namely, S. flexneri 2a, S. flexneri 3a, S. flexneri 6 and S. sonnei I, in a 1:1:1:1 ratio. Adult BALB/c mice were orally immunized in a prime-boost-boost manner. Tetravalent Shigella OMVs immunogen induced significant and persistent serum and mucosal antibodies against OMVs, Outer Membrane Proteins (OMPs) and lipopolysaccharides (LPS). Tetravalent OMVs also primed cell mediated immune response effectively. Protective efficacy against six heterologous Shigella strains was checked in an intra-peritoneal mouse model. Immunized mice survived lethal infection better than the non-immunized mice cohort with fewer replicating bacteria isolated from their gut. This study establishes the possibilities of tetravalent OMVs immunogen to become a potent vaccine candidate against human shigellosis, overcoming the limitations of sero-specific cross-protection of Shigella species.

An Experimental Adult Zebrafish Model for Shigella Pathogenesis, Transmission, and Vaccine Efficacy Studies.

Shigellosis has been a menace to society for ages. The absence of an effective vaccine against Shigella, improper sanitation, and unhygienic use of food and water allow the disease to flourish. Shigella can also be transmitted via natural water bodies. In the absence of a good animal model, the actual nature of pathogenesis and transmission remains unclear. Zebrafish larvae have previously been described as a model for Shigella pathogenesis. However, larval fish lack a mature intestinal microbiota and immune system. Here, the adult zebrafish was assessed as a potential model for Shigella pathogenesis. Their well-developed innate and adaptive immune responses mimic the mammalian immune system. Shigella showed a clear dose-, time-, and temperature-dependent colonization of the adult zebrafish gut. Efficacy of a three-dose immunization regime was tested using bath immunization with heat-killed trivalent Shigella immunogen. The present study demonstrates the efficacy of an adult zebrafish model for pathogenesis, transmission, and vaccine efficacy studies. IMPORTANCE Shigellosis is a diarrheal disease that is prevalent in developing countries and especially dangerous in young children. Currently, animal models for shigellosis are unable to model some aspects of the infectious cycle. Here, we describe a new shigellosis model in adult zebrafish, an increasingly common model organism for studying bacterial pathogens. The zebrafish model can be used to study Shigella colonization, transmission, and immune responses, as well as test vaccine efficacy.

Development of a novel trivalent invasive non-typhoidal Salmonella outer membrane vesicles based vaccine against salmonellosis and fowl typhoid in chickens.

Poultry animals act as natural reservoirs of invasive non-typhoidal Salmonella [iNTS] serovars and consumption of iNTS contaminated poultry meat and eggs is one of the major sources of iNTS infection in developed and developing countries. Irrational use of antibiotics in the poultry industry gives rise to the global emergence of multi drug resistant iNTS strains. Among different strategies to control iNTS infection in poultry farms, vaccination is now being widely used. There are several licensed vaccines available in the market for poultry animals to ameliorate iNTS infection but none of them have broad spectrum protective efficacy. In this study we have formulated a single novel trivalent iNTS outer membrane vesicles [OMVs] based immunogen which can confer long term broad spectrum protection against most prevalent iNTS serovars. We have isolated OMVs from Salmonella Typhimurium [ST], Salmonella Enteritidis [SE], and Salmonella Gallinarum [SG] and formulated the trivalent immunogen by mixing OMVs in a 1:1:1 ratio. One day old chicks were immunized thrice via oral route at two week intervals. Vaccination significantly induced serovar specific antibodies detected up to 180 days post immunization. Post challenge with both homologous and heterologous [S. Infantis] serovars, immunized birds showed reduced level of fecal shedding and organ invasion. A long term efficacy study also showed reduced levels of tissue invasion up to one year post immunization. These results demonstrate that our novel formulation of immunogen could be a broad spectrum potential vaccine for both layer and broiler breeds against iNTS mediated salmonellosis and fowl typhoid.

Development of a Self-Adjuvanting, Cross-Protective, Stable Intranasal Recombinant Vaccine for Shigellosis.

With the acquirement of antibiotic resistance, Shigella has resulted in multiple epidemics of shigellosis, an infectious diarrheal disease, causing thousands of deaths per year. Unfortunately, there are no licensed vaccines, primarily due to low or serotype-specific immunogenicity. Thus, conserved subunit vaccines utilizing recombinant invasion plasmid antigens (Ipa) have been explored as cross-protective vaccine candidates. However, achieving cross-protection against Shigella dysenteriae 1, which caused multiple pandemics/epidemics in the recent past, has been difficult. Therefore, a rational approach to improve cross-protection in the preparation for a possible pandemic should involve conserved proteins from S. dysenteriae 1 (Sd1). IpaC is one such conserved immunogenic protein that is less explored as an independent vaccine due to its instability/aggregation. Therefore, to improve cross-protection and potential immunogenicity and to be prepared for a future epidemic/pandemic, herein, we stabilized recombinant Sd1 IpaC, expressed without its chaperone, using a previously reported stabilizing detergent (LDAO) in a modified protocol and assessed its vaccine potential without an adjuvant. The protein assembled into heterogeneous complex spherical structures in the presence of LDAO and showed improved stability at storage temperatures of -80, -20, 4, 25, and 37 °C while providing enhanced yield and concentration. The protein could also be stably lyophilized and reconstituted, increasing the convenience of transportation and storage. Upon intranasal administration in BALB/c mice, the stabilized-IpaC-immunized groups generated significant antibody response and were not only protected against a high intraperitoneal dose of homologous S. dysenteriae 1 but also showed 100% survival against heterologous Shigella flexneri 2a without an adjuvant, while the control animals showed visible diarrhea (bloody-Sd1 challenge), lethargy, and weight loss with 0% survival. Overall, this work demonstrates that stabilized IpaC can be explored as a minimalist, self-adjuvanting, cross-protective, intranasal, single-antigen Shigella vaccine.

Bivalent non-typhoidal Salmonella outer membrane vesicles immunized mice sera confer passive protection against gastroenteritis in a suckling mice model.

Invasive non-typhoidal Salmonella (iNTS) serovars, especially Salmonella Typhimurium (ST) and Salmonella Enteritidis (SE), cause gastroenteritis worldwide. Due to the emergence of multi-drug resistance in iNTS, a broad-spectrum vaccine is urgently needed for the prevention of iNTS infection. Currently, there is no effective licensed vaccine against iNTS available in the market. We have formulated an outer membrane vesicles (OMVs) based bivalent immunogen as a vaccine candidate to generate broad-spectrum protective immunity against both recently circulating prevalent ST and SE. We have isolated OMVs from ST and SE and formulated the immunogen by mixing both OMVs (1:1 ratio). Three doses of bivalent immunogen significantly induced humoral immune responses against lipopolysaccharides (LPSs) and outer membrane proteins (OMPs) as well as a cell-mediated immune response in adult mice. We also observed that proteins of OMVs act as an adjuvant for generation of high levels of anti-LPS antibodies through T cell activation. We then characterized the one-day old suckling mice model for both ST and SE mediated gastroenteritis and used the model for a passive protection study. In the passive protection study, we found the passive transfer of bivalent OMVs immunized sera significantly reduced ST and SE mediated colonization and gastroenteritis symptoms in the colon of suckling mice compared to non-immunized sera recipients. The overall study demonstrated that OMVs based bivalent vaccine could generate broad-spectrum immunity against prevalent iNTS mediated gastroenteritis. This study also established the suckling mice model as a suitable animal model for vaccine study against iNTS mediated gastroenteritis.

Molecular insights into the genome dynamics and interactions between core and acquired genomes of Vibrio cholerae.

Bacterial species are hosts to horizontally acquired mobile genetic elements (MGEs), which encode virulence, toxin, antimicrobial resistance, and other metabolic functions. The bipartite genome of Vibrio cholerae harbors sporadic and conserved MGEs that contribute in the disease development and survival of the pathogens. For a comprehensive understanding of dynamics of MGEs in the bacterial genome, we engineered the genome of V. cholerae and examined in vitro and in vivo stability of genomic islands (GIs), integrative conjugative elements (ICEs), and prophages. Recombinant vectors carrying the integration module of these GIs, ICE and CTXΦ, helped us to understand the efficiency of integrations of MGEs in the V. cholerae chromosome. We have deleted more than 250 acquired genes from 6 different loci in the V. cholerae chromosome and showed contribution of CTX prophage in the essentiality of SOS response master regulator LexA, which is otherwise not essential for viability in other bacteria, including Escherichia coli In addition, we observed that the core genome-encoded RecA helps CTXΦ to bypass V. cholerae immunity and allow it to replicate in the host bacterium in the presence of similar prophage in the chromosome. Finally, our proteomics analysis reveals the importance of MGEs in modulating the levels of cellular proteome. This study engineered the genome of V. cholerae to remove all of the GIs, ICEs, and prophages and revealed important interactions between core and acquired genomes.

Studies on formulation of a combination heat killed immunogen from diarrheagenic Escherichia coli and Vibrio cholerae in RITARD model.

Multiple diarrheagenic enteric bacterial infections cause global morbidity and mortality. A combination vaccine is needed to combat different diarrhea-causing organisms. In our present work, we formulated a combination of antigens from three different diarrheagenic Escherichia coli strains and three different Vibrio cholerae strains. We demonstrated that our newly formulated combination immunogen was able to raise species-specific immunogenicity. This formulation also gave protection against different diarrheagenic E. coli strains in the removable intestinal tie-adult rabbit diarrhea model. However, protective efficacy was not found against the V. cholerae El Tor Ogawa Haitian variant, but challenged with V. cholerae El Tor Inaba or O139 showed protection in rabbits. This is the first report of a single formulated nonliving heat-killed combination immunogen from different diarrheagenic E. coli and V. cholerae that could bestow protection against different bacteria in an animal model.

Development of a novel S. Typhi and Paratyphi A outer membrane vesicles based bivalent vaccine against enteric fever.

Salmonella Typhi and Salmonella Paratyphi A are the leading causative agents of enteric fever which cause morbidity and mortality worldwide. Currently, there is no combination vaccine which could protect infection from both the strains. In this paper, we are focusing on the development of a novel bivalent typhoidal Outer Membrane Vesicles (OMVs) based immunogen against enteric fever. We have isolated Salmonella Typhi and Paratyphi A OMVs and also characterized OMVs associated antigens. Then we immunized adult mice with three doses of our newly formulated bivalent immunogen orally (25 µg/200 µl). After three doses of oral immunization, we found our immunogen could significantly induce humoral response. We have also found serum IgG against LPS, Vi-polysaccharide etc. OMV immunization induces CD4, CD8 and CD19 population in immunized mice spleen. It also induces Th1 and Th17-cell mediated immunity. We also found bivalent OMVs immunization can prevent more than lethal dose of heterologous Salmonella strains mediated systemic infection in adult mice model. We determined that, the protective immune responses depend on the humoral and cell-mediated immune response. Furthermore, we have evaluated the mode of protective immune response carried out by anti-OMVs antibody by significantly inhibiting bacterial motility and mucin penetration ability. Taken together, these findings suggest that our bivalent immunogen could be used as a novel candidate vaccine against enteric fever.

A brief review on the immunological scenario and recent developmental status of vaccines against enteric fever.

Enteric fever has been one of the leading causes of severe illness and deaths worldwide. S. Typhi and S. Paratyphi A, B and C are important enteric fever-causing organisms globally. This infection causes about 21 million cases among which 222,000 typhoid related deaths occurred in 2015. These estimates do not reflect the ultimate and real status of the disease due to the lack of unified diagnostic and proper reporting system from typhoid endemic and other regions. Current control strategies have become increasingly ineffective due to the emergence of multi-drug resistance among the strains. This situation worsens the disease-burden in developing as well as in developed countries. Moreover the emergence of S. Paratyphi A as a major enteric fever-causing organism in several Asian countries, demands a prophylactic measure at this hour. Other than two licensed vaccines of S. Typhi, there are no exsisting vaccines for S. Paratyphi A. Moreover, travelers returning from endemic regions are becoming more susceptible to have these infections. In this situation, a need for bivalent approach is required where a single immunogen (consisting from each organism) will be effective against the disease. In this review, we have focused on the general information about typhoidal fever, its spread and epidemiology in brief and the present status of typhoidal vaccines and its future. This review highlights existing gaps in the typhoidal salmonellae research with a special emphasis on the status of present typhoidal salmonellae vaccine research.

Zebrafish as a novel model for non-typhoidal Salmonella pathogenesis, transmission and vaccine efficacy.

Salmonella-induced gastroenteritis causes massive morbidity and mortality in both adults and children of developing countries. However, it is difficult to study the mode of infection and vaccine efficacy due to inadequacies of current animal models. For this reason, we have explored using zebrafish as an improved model for non-typhoidal Salmonella (NTS) infection, including Salmonella enterica Typhimurium, Salmonella enterica Enteritidis and Salmonella enterica Weltevreden. In this study, we found that after infection of zebrafish with NTS, severe diarrhea like symptoms were observed and NTS significantly colonized the zebrafish intestine without any manipulation of the normal intestinal microbiota of the fish. Furthermore, these strains can colonize for longer than 72h and induce severe inflammation in the intestine, which may induce fish death. We also found that infected fish can transmit the pathogen into naïve fish. Moreover, we have established that zebrafish is an excellent model for vaccine study. Successive triple bath vaccination with heat-killed single serotype S. Typhimurium and S. Enteritidis immunogen induced protective efficacy against a high dose (10(8)CFU/ml) of infection with these pathogens. This study provides a natural infection model for the study of NTS infection, transmission and vaccine efficacy.