Subcutaneous vaccination with attenuated Salmonella enterica serovar Choleraesuis C500 expressing recombinant filamentous hemagglutinin and pertactin antigens protects mice against fatal infections with both S. enterica serovar Choleraesuis and Bordetella bronchiseptica

C500 variants conveying complete mucosal immunity against fatal infections of pigs with Salmonella enterica serovar Choleraesuis C78-1 or F18+ Shiga toxin-producing Escherichia coli

Salmonella enterica serovar Choleraesuis (S. Choleraesuis) C500 strain is a live, attenuated vaccine strain that has been used in China for over 40 years to prevent piglet paratyphoid. However, this vaccine is limited by its toxicity and does not offer protection against diseases caused by F18+ Shiga toxin-producing Escherichia coli (STEC), which accounts for substantial economic losses in the swine industry. We recently generated a less toxic derivative of C500 strain with both asd and crp deletion (S. Choleraesuis C520) and assessed its efficacy in mice. In addition, we demonstrate that C520 is also less toxic in pigs and is effective in protecting pigs against S. Choleraesuis when administered orally. To develop a vaccine with a broader range of protection, we prepared a variant of C520 (S. Choleraesuis C522), which expresses rSF, a fusion protein comprised of the fimbriae adhesin domain FedF and the Shiga toxin-producing IIe B domain antigen. For comparison, we also prepared a control vector strain (S. Choleraesuis C521). After oral vaccination of pigs, these strains contributed to persistent colonization of the intestinal mucosa and lymphoid tissues and elicited both cytokine expression and humoral immune responses. Furthermore, oral immunization with C522 elicited both S. Choleraesuis and rSF-specific immunoglobulin G (IgG) and IgA antibodies in the sera and gut mucosa, respectively. To further evaluate the feasibility and efficacy of these strains as mucosal delivery vectors via oral vaccination, we evaluated their protective efficacy against fatal infection with S. Choleraesuis C78-1, as well as the F18+ Shiga toxin-producing Escherichia coli field strain Ee, which elicits acute edema disease. C521 conferred complete protection against fatal infection with C78-1; and C522 conferred complete protection against fatal infection with both C78-1 and Ee. Our results suggest that C520, C521, and C522 are competent to provide complete mucosal immune protection against fatal infection with S. Choleraesuis in swine and that C522 equally qualifies as an oral vaccine vector for protection against F18+ Shiga toxin-producing Escherichia coli.

Pathogenicity of Bordetella bronchiseptica isolated from apparently healthy rabbits in guinea pig, rat, and mouse

Bordetella bronchiseptica (B. bronchiseptica) is associated with respiratory tract infections in laboratory animals. In our laboratory animal facility, B. bronchiseptica was isolated from 21 of 27 apparently healthy rabbits obtained from a breeding farm contaminated with B. bronchiseptica. Restriction fragment length polymorphism (RFLP) analysis showed that the flagellin genotype of isolates from the laboratory animal facility and breeding farm was type A, which is seen relatively frequently in rabbits in Europe. To examine its pathogenicity, guinea pigs, rats, and mice were inoculated intranasally with a representative strain isolated in the laboratory animal facility. Following inoculation of 107 colony forming unit (cfu), severe inflammation was observed in the lungs of guinea pig and mice, although the inflammation was less severe in rats. The strain was recovered from the trachea and lungs of these species after inoculation with lower dose such as 103 or 104 cfu. These results suggest that the isolated strain causes respiratory tract infection in guinea pigs, rats, and mice, and that its pathogenicity higher in mice than in rats. This study extends our knowledge of interpreting the microbiologic status of laboratory animals, which will contribute to the development of reliable and reproducible animal experiments.

Evaluation of Safety and Protective Efficacy of a waaJ and spiC Double Deletion Korean Epidemic Strain of Salmonella enterica Serovar Gallinarum

With an aim to develop a highly attenuated and strongly immunogenic distinguishable vaccine candidate, a waaJ (a gene involved in the synthesis of lipopolysaccharide) and spiC (a virulence gene) double deletion Korean epidemic strain of S. enterica ser. Gallinarum (SG005) was constructed. Our results showed that the growth and biochemical characteristics were not altered by this double deletion. The double deletion strain contained dual markers. One was a bacteriological marker (rough phenotype) and the other was a serological marker helping distinguish infected chickens from vaccinated chickens. The double deletion strain showed good genetic stability and reduced resistance to environmental stresses in vitro; furthermore, it was extremely safe and highly avirulent in broilers. Single intramuscular or oral immunization of 7-day-old broilers with the double deletion strain could stimulate the body to produce antibody levels similar to the conventional vaccine strain SG9R. In addition, against a lethal wild-type challenge, it conferred effective protection that was comparable to that seen in the group vaccinated with SG9R. In conclusion, this double deletion strain may be an effective vaccine candidate for controlling S. enterica ser. Gallinarum infection in broilers.

Secretory System Components as Potential Prophylactic Targets for Bacterial Pathogens

Bacterial secretory systems are essential for virulence in human pathogens. The systems have become a target of alternative antibacterial strategies based on small molecules and antibodies. Strategies to use components of the systems to design prophylactics have been less publicized despite vaccines being the preferred solution to dealing with bacterial infections. In the current review, strategies to design vaccines against selected pathogens are presented and connected to the biology of the system. The examples are given for Y. pestis, S. enterica, B. anthracis, S. flexneri, and other human pathogens, and discussed in terms of effectiveness and long-term protection.

Isolation, Antimicrobial Resistance Phenotypes, and Virulence Genes of Bordetella bronchiseptica From Pigs in China, 2018-2020

Bordetella bronchiseptica is a leading cause of respiratory diseases in pigs. However, epidemiological data of B. bronchiseptica in pigs particularly in China, the largest pig rearing country in the world is still limited. We isolated 181 B. bronchiseptica strains from 4259 lung samples of dead pigs with respiratory diseases in 14 provinces in China from 2018 to 2020. The average isolation rate of this 3-year period was 4.25% (181/4259). Antimicrobial susceptibility testing performed by disc diffusion method revealed that most of the B. bronchiseptica isolates in this study were resistant to ampicillin (83.98%), while a proportion of isolates were resistant to cefotaxime (30.39%%), chloramphenicol (12.71%), gentamicin (11.60%), florfenicol (11.60%), tetracycline (8.84%), amoxicillin (8.29%), tobramycin (6.63%), ceftriaxone (4.97%), and cefepime (0.55%). There were no isolates with resistant phenotypes to imipenem, meropenem, polymyxin B, ciprofloxacin, enrofloxacin, and amikacin. In addition, ~13.18% of the isolates showed phenotypes of multidrug resistance. Detection of antimicrobial resistance genes (ARGs) by PCR showed that 16.57% of the B. bronchiseptica isolates in this study was positive to aac(3)-IV, while 3.87%, 2.21%, 1.10%, 0.55%, 0.55%, and 0.55% of the isolates were positive to aac6'-Ib, rmtA, bla_TEM, bla_SHV, oqxB, and tetA, respectively. Detection of virulence factors encoding genes (VFGs) by conventional PCR showed that over 90% of the pig B. bronchiseptica isolates in this study were positive to the five VFGs examined (fhaB, 97.24%; prn, 91.16%; cyaA, 98.34%; dnt, 98.34%; betA, 92.82%). These results demonstrate B. bronchiseptica as an important pathogen associated with pig respiratory disorders in China. The present work contributes to the current understanding of the prevalence, antimicrobial resistance and virulence genes of B. bronchiseptica in pigs.

H2O2-Inactivated Salmonella typhimurium RE88 Strain as a New Cancer Vaccine Carrier: Evaluation in a Mouse Model of Cancer

Purpose

This study aimed to describe a novel cancer vaccine developed using H₂O₂-inactivated Salmonella typhimurium RE88 [with deletions of AroA (the first enzyme in the aromatic amino acid biosynthesis pathway) and DNA adenine methylase] as the carrier.

Methods

The pVLT33 plasmid was used to engineer an RE88 strain induced to express ovalbumin (OVA) by isopropylthiogalactoside (RE88-pVLT33-OVA). The immune responses and anticancer effects of H₂O₂-inactivated RE88-pVLT33-OVA were compared with those of non-inactivated RE88-pVLT33-OVA and OVA (positive control) in mice carrying OVA-expressing tumors (EG7-OVA) cells.

Results

Anti-ovalbumin IgG (immunoglobulin G) titer following vaccination with H₂O₂-inactivated RE88-pVLT33-OVA was higher for subcutaneous than for intragastric vaccination. When subcutaneous administration was used, H₂O₂-inactivated RE88-pVLT33-OVA (2 × 10⁹ CFU (colony forming units)/mouse) achieved an anti-ovalbumin IgG titer higher than that for the same dose of RE88-pVLT33-OVA and comparable to that for 10 µg ovalbumin (positive control). The binding of mouse serum antibodies to EG7-OVA cells was stronger for H₂O₂-inactivated RE88-pVLT33-OVA (2 × 10⁹ CFU/mouse) than for 10 µg ovalbumin. Furthermore, subcutaneous vaccination with H₂O₂-inactivated RE88-pVLT33-OVA (2 × 10⁹ CFU/mouse) induced greater activation of splenic T cells and more extensive tumor infiltration with CD4⁺/CD8⁺ T cells compared with 10 µg ovalbumin (positive control). The mice vaccinated subcutaneously with H₂O₂-inactivated RE88-pVLT33-OVA at a dose of 2 × 10⁸ or 6 × 10⁸ CFU/mouse had smaller tumors compared with mice in the negative control groups. Tumor weight in mice vaccinated with H₂O₂-inactivated RE88-pVLT33-OVA at a dose of 2 × 10⁹ CFU/mouse was significantly lower than that in both negative control groups (P < 0.05) and decreased with the increasing dose of H₂O₂-inactivated RE88-pVLT33-OVA. H₂O₂-inactivated RE88-pVLT33-OVA was potentially safer than the non-inactivated strain, could carry exogenous antigens, and had specific epitopes that could be exploited as natural adjuvants to facilitate the induction of cellular and humoral immune responses.

Conclusion

It was anticipated that H₂O₂-inactivated RE88-pVLT33-OVA could be used as a novel delivery system for new cancer vaccines.

Live-attenuated Salmonella enterica serotype Choleraesuis vaccine with regulated delayed fur mutation confer protection against Streptococcus suis in mice

Background

Recombinant Salmonella enterica serotype Choleraesuis (S. Choleraesuis) vaccine vector could be used to deliver heterologous antigens to prevent and control pig diseases. We have previously shown that a live-attenuated S. Choleraesuis vaccine candidate strain rSC0011 (ΔP_crp527::TT araC P_BADcrp Δpmi-2426 ΔrelA199::araC P_BADlacI TT ΔasdA33, Δ, deletion, TT, terminator) delivering SaoA, a conserved surface protein in most of S. suis serotypes, provided excellent protection against S. suis challenge, but occasionally lead to morbidity (enteritidis) in vaccinated mice (approximately 1 in every 10 mice). Thus, alternated attenuation method was sought to reduce the reactogenicity of strain rSC0011. Herein, we described another recombinant attenuated S. Choleraesuis vector, rSC0012 (ΔP_fur88:: TT araC P_BADfur Δpmi-2426 ΔrelA199:: araC P_BADlacI TT ΔasdA33) with regulated delayed fur mutation to avoid inducing disease symptoms while exhibiting a high degree of immunogenicity.

Results

The strain rSC0012 strain with the ΔP_fur88::TT araC P_BADfur mutation induced less production of inflammatory cytokines than strain rSC0011 with the ΔP_crp527::TT araC P_BADcrp mutation in mice. When delivering the same pS-SaoA plasmid, the intraperitoneal LD₅₀ of rSC0012 was 18.2 times higher than that of rSC0011 in 3-week-old BALB/C mice. rSC0012 with either pS-SaoA or pYA3493 was cleared from spleen and liver tissues 7 days earlier than rSC0011 with same vectors after oral inoculation. The strain rSC0012 synthesizing SaoA induced high titers of anti-SaoA antibodies in both systemic (IgG in serum) and mucosal (IgA in vaginal washes) sites, as well as increased level of IL-4, the facilitator of Th2-type T cell immune response in mice. The recombinant vaccine rSC0012(pS-SaoA) conferred high percentage of protection against S. suis or S. Choleraesuis challenge in BALB/C mice.

Conclusions

The live-attenuated Salmonella enterica serotype Choleraesuis vaccine rSC0012(pS-SaoA) with regulated delayed fur mutation provides a foundation for the development of a safe and effective vaccine against S. Choleraesuis and S. suis.

Subcutaneous vaccination with a live attenuated Yersinia pseudotuberculosis plague vaccine

A single oral inoculation to mice of the live attenuated Yersinia pseudotuberculosis VTnF1 strain producing an F1 pseudocapsule protects against bubonic and pneumonic plague. However oral vaccination can fail in humans exposed to frequent intestinal infections. We evaluated in mice the efficacy of subcutaneous vaccine injection as an alternative way to induce protective immunity, while reducing the dose and avoiding strain release in nature. A single subcutaneous dose of up to 10⁸ CFU induced dose-dependent antibody production. At the dose of 10⁷ CFU, i.e. 10 times less than via the oral route, it caused a modest skin reaction and protected 100% against bubonic and 80% against pneumonic plague, caused by high doses of Yersinia pestis. Bacteria migrating to lymph nodes and spleen, but not feces, were rapidly eliminated. Thus, subcutaneous injection of VTnF1 would represent a good alternative when dissemination in nature and human intestinal responsiveness are limitations.

A Marker-Free Bordetella bronchiseptica aroA/bscN Double Deleted Mutant Confers Protection Against Lethal Challenge

Bordetella bronchiseptica is a leading cause of swine respiratory disorders which depict a great threat to well-flourished porcine industry. Vaccination remains an effective way for the prevention of B. bronchiseptica infections, as live B. bronchiseptica vaccines possess many advantages compared to inactivated vaccines and/or sub-unit vaccines, however, their safety is not up to the mark. In present study, we constructed marker-free aroA/bscN double deleted B. bronchiseptica QH09 through two-step homologous recombination strategy. Our data showed that QH09 attenuated virulence to mice compared with the parent aroA deleted B. bronchiseptica QH0814. We also found that QH09 meets the vaccine safety standards, upon challenge in piglets, did not cause any visible clinical signs or lesions on organs. Finally, we demonstrated that vaccination of QH09 activated the systemic as well as the mucosal immunity in pigs and provided protection against lethal bacterial challenge. These findings suggest that the aroA/bscN double deleted B. bronchiseptica QH09 may be an effective vaccine candidate, with safety assurance of animals against B. bronchiseptica infections.

Salmonella enterica serovar Choleraesuis vector delivering SaoA antigen confers protection against Streptococcus suis serotypes 2 and 7 in mice and pigs

Streptococcus suis is one of the major pathogens that cause economic losses in the swine industry worldwide. However, current bacterins only provide limited prophylactic protection in the field. An ideal vaccine against S. suis should protect pigs against the clinical diseases caused by multiple serotypes, or at least protect against the dominant serotype in a given geographic region. A new recombinant Salmonella enterica serotype Choleraesuis vaccine vector, rSC0011, that is based on the regulated delayed attenuation system and regulated delayed antigen synthesis system, was developed recently. In this study, an improved recombinant attenuated Salmonella Choleraesuis vector, rSC0016, was developed by incorporating a sopB mutation to ensure adequate safety and maximal immunogenicity. In the spleens of mice, rSC0016 colonized less than rSC0011. rSC0016 and rSC0011 colonized similarly in Peyer's patches of mice. The recombinant vaccine rSC0016(pS-SaoA) induced stronger cellular, humoral, and mucosal immune responses in mice and swine against SaoA, a conserved surface protein that is present in many S. suis serotypes, than did rSC0011(pS-SaoA) without sopB or rSC0018(pS-SaoA), which is an avirulent, chemically attenuated vaccine strain. rSC0016(pS-SaoA) provided 100% protection against S. suis serotype 2 in mice and pigs, and full cross-protection against SS7 in pigs. This new vaccine vector provides a foundation for the development of a universal vaccine against multiple serotypes of S. suis in pigs.

The efficacy, biodistribution and safety of an inhibin DNA vaccine delivered by attenuated Salmonella choleraesuis

DNA vaccines, the third‐generation vaccines, were extensively studied. The attenuated Salmonella choleraesuis (S. choleraesuis) was widely focused as a carrier to deliver DNA vaccines in the chromosome–plasmid balanced‐lethal system. The efficacy of inhibin DNA vaccine delivered by attenuated S. choleraesuis was proved in mice and cows in our previous studies. In this study, the efficacy of inhibin DNA vaccine was confirmed in rhesus monkeys. To further study the biodistribution and safety, the mice were immunized under laboratory conditions. The results of the rhesus monkeys showed the plasma IgA and IgG titres against inhibin were elevated, and the oestradiol (E₂) and progesterone (P₄) levels were increased with immunizing inhibin DNA vaccine. The biodistribution and safety assessment displayed the body weight, pathological change and haematology indexes where there is no significant difference between vaccinated mice and control. And the genomics analysis showed there was no integration of the inhibin gene into the mouse genome 2 months after immunization. This study indicated the inhibin DNA vaccine delivered by attenuated S. choleraesuis was safe. And this vaccine was a potential means to improve their reproductive traits in primates and other animals.

Mucosal IgA and IFN-γ+ CD8 T cell immunity are important in the efficacy of live Salmonella enteria serovar Choleraesuis vaccines

Salmonellosis, a disease caused by non-typhoidal Salmonella strains which can be transmitted from swine to humans, is one of the leading public health problems around the world. Paratyphoid of swine is controlled by vaccinating swine with Salmonella enterica serovar Choleraesuis (S. Choleraesuis) live vaccine strain C500 in China. Although the vaccine has good prophylactic efficacy, the mechanism of immunogenicity is unclear. Using a C500-derived paratyphoid thermo-stable live vaccine (PTSL vaccine), we demonstrated that the PTSL vaccine induces strong primary and memory immune responses in piglets. Mucosal IgA and IFN-γ⁺/CD8⁺ T cells induced by the PTSL vaccine play key roles in the protection of the host from Salmonella infection. Our findings have important implications on the development of new and improved vaccines against salmonellosis and using live-attenuated Salmonella as vaccine carriers.

Plant-based vaccines against respiratory diseases: current status and future prospects

INTRODUCTION

Respiratory infections have an enormous, worldwide epidemiologic impact on humans and animals. Among the prophylactic measures, vaccination has the potential to neutralize this impact. New technologies for vaccine production and delivery are of importance in this field since they offer the potential to develop new immunization approaches overriding the current limitations that comprise high cost, safety issues, and limited efficacy. Areas covered: In the present review, the state of the art in developing plant-based vaccines against respiratory diseases is presented. The review was based on the analysis of current biomedical literature. Expert commentary: Preclinical and clinical evaluations of several vaccine candidates against influenza, tuberculosis, respiratory syncytial virus, pneumonia, anthrax and asthma are discussed and placed in perspective.

Salmonella Typhimurium strain expressing OprF-OprI protects mice against fatal infection by Pseudomonas aeruginosa

Pseudomonas aeruginosa poses a major threat to human health and to the mink industry. Thus, development of vaccines that elicit robust humoral and cellular immunity against P. aeruginosa is greatly needed. In this study, a recombinant attenuated Salmonella vaccine (RASV) that expresses the outer membrane proteins fusion OprF190-342 -OprI21-83 (F1I2) from P. aeruginosa was constructed and the potency of this vaccine candidate assessed by measuring F1I2-specific humoral immune responses upon vaccination through s.c. or oral routes. S.C. administration achieved higher serum IgG titers and IgA titers in the intestine and induced stronger F1I2-specific IgG and IgA titers in lung homogenate than did oral administration, which resulted in low IgG titers and no local IgA production. High titers of IFN-γ, IL-4, and T-lymphocyte subsets induced a mixed Th1/Th2 response in mice immunized s.c., indicating elicitation of cellular immunity. Importantly, when immunized mice were challenged with P. aeruginosa by the intranasal route 30 days after the initial immunization, s.c. vaccination achieved 77.78% protection, in contrast to 41.18% via oral administration and 66.67% via Escherichia coli-expressed F1I2 (His-F1I2) vaccination. These results indicate that s.c. vaccination provides a better protective response against P. aeruginosa infection than do oral administration and the His-F1I2 vaccine.

Virulence characteristics of extraintestinal pathogenic Escherichia coli deletion of gene encoding the outer membrane protein X

Outer membrane protein X (OmpX) and its homologues have been proposed to contribute to the virulence in various bacterial species. But, their role in virulence of extraintestinal pathogenic Escherichia coli (ExPEC) is yet to be determined. This study evaluates the role of OmpX in ExPEC virulence in vitro and in vivo using a clinical strain PPECC42 of porcine origin. The ompX deletion mutant exhibited increased swimming motility and decreased adhesion to, and invasion of pulmonary epithelial A549 cell, compared to the wild-type strain. A mild increase in LD₅₀ and distinct decrease in bacterial load in such organs as heart, liver, spleen, lung and kidney were observed in mice infected with the ompX mutant. Complementation of the complete ompX gene in trans restored the virulence of mutant strain to the level of wild-type strain. Our results reveal that OmpX contributes to ExPEC virulence, but may be not an indispensable virulence determinant.

Construction of a bivalent DNA vaccine co-expressing S genes of transmissible gastroenteritis virus and porcine epidemic diarrhea virus delivered by attenuated Salmonella typhimurium

Porcine transmissible gastroenteritis virus (TGEV) and porcine epidemic diarrhea virus (PEDV) can cause severe diarrhea in newborn piglets and led to significant economic losses. The S proteins are the main structural proteins of PEDV and TGEV capable of inducing neutralizing antibodies in vivo. In this study, a DNA vaccine SL7207 (pVAXD-PS1-TS) co-expressing S proteins of TGEV and PEDV delivered by attenuated Salmonella typhimurium was constructed and its immunogenicity in piglets was investigated. Twenty-day-old piglets were orally immunized with SL7207 (pVAXD-PS1-TS) at a dosage of 1.6 × 10(11) CFU per piglet and then booster immunized with 2.0 × 10(11) CFU after 2 weeks. Humoral immune responses, as reflected by virus neutralizing antibodies and specific IgG and sIgA, and cellular immune responses, as reflected by IFN-γ, IL-4, and lymphocyte proliferation, were evaluated. SL7207 (pVAXD-PS1-TS) simultaneously elicited immune responses against TGEV and PEDV after oral immunization. The immune levels started to increase at 2 weeks after immunization and increased to levels statistically significantly different than controls at 4 weeks post-immunization, peaking at 6 weeks and declined at 8 weeks. The humoral, mucosal, and cellular immune responses induced by SL7207 (pAXD-PS1-TS) were significantly higher than those of the PBS and SL7207 (pVAXD) (p < 0.01). In particular, the levels of IFN-γ and IL-4 were higher than those induced by the single-gene vaccine SL7207 (pVAXD-PS1) (p < 0.05). These results demonstrated that SL7207 (pVAXD-PS1-TS) possess the immunological functions of the two S proteins of TGEV and PEDV, indicating that SL7207 (pVAXD-PS1-TS) is a candidate oral vaccine for TGE and PED.

Complete Genome Sequence of Salmonella enterica Serovar Choleraesuis Vaccine Strain C500 Attenuated by Chemical Mutation

Salmonella enterica serovar Choleraesuis strain C500 is a live vaccine attenuated by chemical methods. Here, we report the complete genome sequence of the strain, which may be helpful for elucidating the attenuation mechanism of the vaccine strain.

Immunologic study and optimization of Salmonella delivery strains expressing adhesin and toxin antigens for protection against progressive atrophic rhinitis in a murine model

Mice were intranasally inoculated at various times to optimize the vaccination strategy with a new live candidate vaccine expressing the antigens CP39, FimA, PtfA, and ToxA of Pasteurella multocida and F1P2 of Bordetella bronchiseptica in an attenuated live Salmonella system to protect against progressive atrophic rhinitis (PAR). Sixty BALB/c mice were divided equally into 4 groups. The group A mice were vaccinated only at 12 wk of age, the group B mice received a primary vaccination at 9 wk of age and a booster at 12 wk of age, the group C mice received a primary vaccination at 6 wk of age and boosters at 9 and 12 wk of age, and the group D mice were inoculated intranasally with sterile phosphate-buffered saline as a control. The humoral and mucosal immune responses of groups A, B, and C increased significantly compared with those of the control group. Expression of the cytokines interleukin-4 and interferon-γ in splenocytes also increased significantly. In addition, the group B mice exhibited significantly fewer gross lesions in lung tissue compared with the other vaccinated groups after challenge with a virulent P. multocida strain. These results indicate that a strategy of double intranasal vaccination can optimize protection against PAR.

TolC promotes ExPEC biofilm formation and curli production in response to medium osmolarity

While a high osmolarity medium activates Cpx signaling and causes CpxR to repress csgD expression, and efflux protein TolC protein plays an important role in biofilm formation in Escherichia coli, whether TolC also responds to an osmolarity change to regulate biofilm formation in extraintestinal pathogenic E. coli (ExPEC) remains unknown. In this study, we constructed ΔtolC mutant and complement ExPEC strains to investigate the role of TolC in the retention of biofilm formation and curli production capability under different osmotic conditions. The ΔtolC mutant showed significantly decreased biofilm formation and lost the ability to produce curli fimbriae compared to its parent ExPEC strain PPECC42 when cultured in M9 medium or 1/2 M9 medium of increased osmolarity with NaCl or sucrose at 28°C. However, biofilm formation and curli production levels were restored to wild-type levels in the ΔtolC mutant in 1/2 M9 medium. We propose for the first time that TolC protein is able to form biofilm even under high osmotic stress. Our findings reveal an interplay between the role of TolC in ExPEC biofilm formation and the osmolarity of the surrounding environment, thus providing guidance for the development of a treatment for ExPEC biofilm formation.

Evaluation of efficacy, biodistribution and safety of antibiotic-free plasmid encoding somatostatin genes delivered by attenuated Salmonella enterica serovar Choleraesuis

We describe here a balanced-lethal system using an Asd(+) expression plasmid pVGS/2SS-asd encoding two copies of somatostatin (SS) genes carried by Δasd/Δcrp double mutant Salmonella enterica serovar Choleraesuis (named C501). The advantage of this novel system is the use of asd (aspartate-semialdehyde dehydrogenase) gene as selection marker to replace the antibiotic resistance markers, thus eliminating the industrial cultivation and environmental problems. We then evaluated the efficacy, biodistribution and safety of antibiotic-free plasmid delivered by strains C501. Mice orally immunized with C501 (pVGS/2SS-asd) had significantly higher levels of anti-SS total IgG and IgA antibodies than control mice and demonstrated a bias toward Th2-associated responses (IgG1/IgG2a ratio>1). Safety evaluation indicated that vaccinated mice displayed no abnormal clinical signs and histological changes. Biodistribution result revealed that the GS/2SS message was detected in several examined tissues with the exception of ovary and brain, but was rapidly cleared from the body (approximately 10 days). Furthermore, the risk of integration of plasmid pVGS/2SS-asd into the host cellular genome was considered to be negligible. These results may have important implications for the use of vaccine strain C501 (pVGS/2SS-asd) in domestic animals and prompt new perspectives on the safety of DNA vaccines delivered by attenuated bacteria.

Oral vaccination with inhibin DNA delivered using attenuated Salmonella choleraesuis for improving reproductive traits in mice

The objective of this study was to examine the efficacy and safety of a novel inhibin vaccine containing inhibin α (1-32) fragments in mice. A recombinant plasmid pVAX-asd-IS was constructed by inserting recombinant inhibin α (1-32) and the hepatitis B surface antigen S into the plasmid in which the asd gene, rather than the kanamycin gene, was a selection marker. Ninety Kuming mice were divided into six groups consisting of 15 mice each. First group was (C1) injected with 200 µl of PBS, second (C2) received 1 × 10(10) CFU of crp(-) /asd(-) C500/pVAX-asd and served as vector control, third did not receive any treatment (C3), while fourth, fifth, and sixth group received 1 × 10(10) , 1 × 10(9) , 1 × 10(8) CFU of the recombinant inhibin vaccine crp(-) /asd(-) C500/pVAX-asd-IS (group T1, T2, T3), respectively. Western blotting demonstrated that recombinant expressed inhibin protein possessed immune function and that this plasmid could replicate for up to 40 generations stably. Vaccination with this strain at a dose of 1 × 10(10) CFU/200 µl per mouse induced high anti-inhibin antibody levels, significantly increased large-follicle production in T1 group (p < 0.05) and average litter size (p > 0.05) compared with control groups. Integration studies showed no evidence of inhibin fusion gene integrated into mice's genome 2-month after immunization. These results suggest that the vaccine described in the present study may provide a safe method to improve reproductive traits in animals. A trend towards increased litter size and significant increase in large follicle population depict that this vaccine may have direct application in large animal industry.

Dual mechanism of protection by live attenuated Bordetella pertussis BPZE1 against Bordetella bronchiseptica in mice

Bordetella bronchiseptica, a gram-negative bacterium, causes chronic respiratory tract infections in a wide variety of mammalian hosts, including man, and no human vaccine is currently available. Acellular pertussis vaccines protect poorly against B. bronchiseptica, although they contain cross-reactive antigens. We have recently developed Bordetella pertussis BPZE1, a novel, live attenuated pertussis vaccine, currently completing phase I clinical trials in humans, and found that it protects against both B. pertussis and Bordetella parapertussis in mice. Here, we show that a single nasal administration of BPZE1 protects mice against lethal infection with B. bronchiseptica. After challenge, the vaccinated animals displayed markedly reduced lung inflammation and tissue damage, decreased neutrophil infiltration and increased levels of CD4(+)CD25(+)FoxP3(+) regulatory T cells in the lungs compared to non-immunized mice. Depletion of these cells abolished BPZE1-induced protection, indicating that BPZE1 protects against lethal inflammation through the recruitment of regulatory T cells. In addition, the B. bronchiseptica load was significantly decreased in the vaccinated animals. Using passive transfer experiments, protection was found to be essentially cell mediated, and BPZE1-induced Th1 and Th17 T cells recognize whole B. bronchiseptica extracts, although the participation of antibodies in protection cannot be discounted. Thus, a single administration of BPZE1 can confer protection against B. bronchiseptica in mice by a dual mechanism.

The Burkholderia pseudomallei Δasd mutant exhibits attenuated intracellular infectivity and imparts protection against acute inhalation melioidosis in mice

Burkholderia pseudomallei, the cause of serious and life-threatening diseases in humans, is of national biodefense concern because of its potential use as a bioterrorism agent. This microbe is listed as a select agent by the CDC; therefore, development of vaccines is of significant importance. Here, we further investigated the growth characteristics of a recently created B. pseudomallei 1026b Δasd mutant in vitro, in a cell model, and in an animal model of infection. The mutant was typified by an inability to grow in the absence of exogenous diaminopimelate (DAP); upon single-copy complementation with a wild-type copy of the asd gene, growth was restored to wild-type levels. Further characterization of the B. pseudomallei Δasd mutant revealed a marked decrease in RAW264.7 murine macrophage cytotoxicity compared to the wild type and the complemented Δasd mutant. RAW264.7 cells infected by the Δasd mutant did not exhibit signs of cytopathology or multinucleated giant cell (MNGC) formation, which were observed in wild-type B. pseudomallei cell infections. The Δasd mutant was found to be avirulent in BALB/c mice, and mice vaccinated with the mutant were protected against acute inhalation melioidosis. Thus, the B. pseudomallei Δasd mutant may be a promising live attenuated vaccine strain and a biosafe strain for consideration of exclusion from the select agent list.

Construction of a conditional lethal Salmonella mutant via genetic recombination using the ara system and asd gene

In order to construct a conditional lethal Salmonella mutant, an arabinose-regulated recombinant genetic system was used. The Salmonella aspartate semialdehyde dehydrogenase (asd) gene was localized under the control of araC P(araBAD) in a plasmid to create the araC P(araBAD)::asd cassette. The cassette was cloned into a plasmid carrying a p15A replication origin to create the recombinant plasmid pMMP55. The growth of Salmonella MMP10 harboring pMMP55 was dependent on the presence of arabinose. In the presence of arabinose, the Asd deficiency due to chromosomal deletion of asd in the Salmonella host was complemented by the asd gene transcribed and translated under the P(araBAD) promoter and araBAD Shine-Dalgarno (SD) sequence in pMMP55. Growth inhibition of the strain was demonstrated by arabinose depletion in M9 minimal medium, indicating that the strain were unable to grow in an arabinose-limited environment. In addition, the analysis of a 50% lethal dose (LD50) using mice revealed that the strain MMP10 exhibited attenuation by approximately 100-fold relative to that of the unmodified strain. In conclusion, these data suggest that the araC P(araBAD)::asd system developed in this study can be used to construct conditional lethal Salmonella mutants for application as safe, live-attenuated Salmonella vaccines.

Attenuated Actinobacillus pleuropneumoniae as a bacterial vector for expression of Mycoplasma hyopneumoniae P36 gene

BACKGROUND

Actinobacillus pleuropneumoniae and Mycoplasma hyopneumoniae are causative agents of porcine pneumonia. Over the last few years, attenuated A. pleuropneumoniae live vaccines have been shown to provide protection against A. pleuropneumoniae infection. We postulated that attenuated A. pleuropneumoniae could additionally be used as a vaccine vector for protection against M. hyopneumoniae.

METHODS

A mutant strain of A. pleuropneumoniae, SLW36, was constructed by replacing the urease structural gene of mutant strain SLW03 of A. pleuropneumoniae with the L-lactate dehydrogenase gene (p36) of M. hyopneumoniae by transconjugation and counter selection. The urease function and the growth kinetics of SLW36 were measured. Protein expression of P36 was analyzed by sodium dodecylsulfate-polyacrylamide gel electrophoresis and western blotting. The attenuated virulence and immunity of SLW36 were analyzed in a mouse model.

RESULTS

The mutant strain SLW36 was urease negative and four-fold less virulent than the parental strain SLW03. There were no differences in expression levels of p36 at different culture time-points and the foreign gene was stable after in vitro passage. Immunoglobulin G responses against p36 antigen and M. hyopneumoniae whole-cell antigen were detected.

CONCLUSIONS

The mutant strain SLW36 can induce antibody against p36 and M. hyopneumoniae. The mutant strain SLW36 has the potential to be used as a live vaccine for protection against A. pleuropneumoniae and M. hyopneumoniae. Studies in pigs are needed to confirm protective levels of antibodies and to check for rare side-effects of the vaccine.

Immunogenicity of recombinant protective antigen and efficacy against intranasal challenge with Bordetella bronchiseptica

Bordetella bronchiseptica is a Gram-negative respiratory pathogen that causes substantial disease in a variety of animals. Filamentous hemagglutinin (FHA) and pertactin are important attachment factors and protective immunogens, which serve as protective antigens in several animal models of infection with B. bronchiseptica. Here, we showed the efficacy of subcutaneous immunization of mice with a recombinant protein rF1P2, which consisted of the important immunodominant protective type I domain (F1) of FHA and the highly immunogenic region II domain (P2) of pertactin. Groups of mice tested, when challenged with different strains of B. bronchiseptica were fully protected, with long-lasting immunity to lethal B.bronchiseptica challenge, whereas mice immunized with Freund's adjuvant alone or PBS were not. In rF1P2-immunized mice, specific antibodies lasted for more than 120 days, and the IgG1/IgG2a ratio remained at a constant level till the end of the study. This suggests that rF1P2-induced a long-lasting balanced humoral immune responses and immunological memory in mice. rF1P2-specific antisera inhibited hemagglutination associated with full-length mature FHA. Furthermore, passive antiserum transfer from immunized animals completely protected naive mice from subsequent B. bronchiseptica challenge. These data may have implications for the development of safe and efficacious subunit vaccines for the prevention of bordetellosis, and may contribute to future acellular whooping cough vaccines.