Inhibition of Severe Acute Respiratory Syndrome Coronavirus 2 Replication by Hypertonic Saline Solution in Lung and Kidney Epithelial Cells

An unprecedented global health crisis has been caused by a new virus called severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We performed experiments to test if a hypertonic saline solution was capable of inhibiting virus replication. Our data show that 1.2% NaCl inhibited virus replication by 90%, achieving 100% of inhibition at 1.5% in the nonhuman primate kidney cell line Vero, and 1.1% of NaCl was sufficient to inhibit the virus replication by 88% in human epithelial lung cell line Calu-3. Furthermore, our results indicate that the inhibition is due to an intracellular mechanism and not to the dissociation of the spike SARS-CoV-2 protein and its human receptor. NaCl depolarizes the plasma membrane causing a low energy state (high ADP/ATP concentration ratio) without impairing mitochondrial function, supposedly associated with the inhibition of the SARS-CoV-2 life cycle. Membrane depolarization and intracellular energy deprivation are possible mechanisms by which the hypertonic saline solution efficiently prevents virus replication in vitro assays.

Biosensor-based selective detection of Zika virus specific antibodies in infected individuals

Zika virus (ZIKV) recently emerged as a global threat subsequent to its global spread because it induces microencephaly and other brain damages in infants born to infected mothers. Epidemiological monitoring of infection has been hampered by the absence of reliable serological tests capable to distinguish between ZIKV and other Flavivirus infections, in particular Dengue virus (DENV). As both viruses are transmitted by the same mosquito-species, their distributions largely overlap and reliable serological distinction between the viruses is essential. Here we develop a novel biosensor which is based on recombinant forms of ZIKV non-structural protein 1 (NS1) and the domain III of the envelope protein (EDIII). Using electrochemical impedance spectroscopy (EIS) and square wave voltammetry (SWV), we demonstrate that in addition to extremely sensitive detection of ZIKV-specific antibodies in serum and saliva, the biosensor promptly distinguished ZIKV and DENV-specific antibodies. Hence, this novel biosensor allows assessing ZIKV antibodies in blood and saliva and results are unaffected by presence of DENV virus-specific antibodies.

Induction of resident memory T cells enhances the efficacy of cancer vaccine

Tissue-resident memory T cells (Trm) represent a new subset of long-lived memory T cells that remain in tissue and do not recirculate. Although they are considered as early immune effectors in infectious diseases, their role in cancer immunosurveillance remains unknown. In a preclinical model of head and neck cancer, we show that intranasal vaccination with a mucosal vector, the B subunit of Shiga toxin, induces local Trm and inhibits tumour growth. As Trm do not recirculate, we demonstrate their crucial role in the efficacy of cancer vaccine with parabiosis experiments. Blockade of TFGβ decreases the induction of Trm after mucosal vaccine immunization, resulting in the lower efficacy of cancer vaccine. In order to extrapolate this role of Trm in humans, we show that the number of Trm correlates with a better overall survival in lung cancer in multivariate analysis. The induction of Trm may represent a new surrogate biomarker for the efficacy of cancer vaccine. This study also argues for the development of vaccine strategies designed to elicit them.

Sublingual immunization with the phosphate-binding-protein (PstS) reduces oral colonization by Streptococcus mutans

Bacterial ATP-binding cassette (ABC) transporters play a crucial role in the physiology and pathogenicity of different bacterial species. Components of ABC transporters have also been tested as target antigens for the development of vaccines against different bacterial species, such as those belonging to the Streptococcus genus. Streptococcus mutans is the etiological agent of dental caries, and previous studies have demonstrated that deletion of the gene encoding PstS, the substrate-binding component of the phosphate uptake system (Pst), reduced the adherence of the bacteria to abiotic surfaces. In the current study, we generated a recombinant form of the S. mutans PstS protein (rPstS) with preserved structural features, and we evaluated the induction of antibody responses in mice after sublingual mucosal immunization with a formulation containing the recombinant protein and an adjuvant derived from the heat-labile toxin from enterotoxigenic Escherichia coli strains. Mice immunized with rPstS exhibited systemic and secreted antibody responses, measured by the number of immunoglobulin A-secreting cells in draining lymph nodes. Serum antibodies raised in mice immunized with rPstS interfered with the adhesion of bacteria to the oral cavity of naive mice challenged with S. mutans. Similarly, mice actively immunized with rPstS were partially protected from oral colonization after challenge with the S. mutans NG8 strain. Therefore, our results indicate that S. mutans PstS is a potential target antigen capable of inducing specific and protective antibody responses after sublingual administration. Overall, these observations raise interesting perspectives for the development of vaccines to prevent dental caries.

Role of bacteriophages in STEC infections: new implications for the design of prophylactic and treatment approaches

Shiga toxin (Stx) is considered the main virulence factor in Shiga toxin-producing Escherichia coli (STEC) infections. Previously we reported the expression of biologically active Stx by eukaryotic cells in vitro and in vivo following transfection with plasmids encoding Stx under control of the native bacterial promoter ^1,2. Since stx genes are present in the genome of lysogenic bacteriophages, here we evaluated the relevance of bacteriophages during STEC infection. We used the non-pathogenic E. coli C600 strain carrying a lysogenic 933W mutant bacteriophage in which the stx operon was replaced by a gene encoding the green fluorescent protein (GFP). Tracking GFP expression using an In Vivo Imaging System (IVIS), we detected fluorescence in liver, kidney, and intestine of mice infected with the recombinant E. coli strain after treatment with ciprofloxacin, which induces the lytic replication and release of bacteriophages. In addition, we showed that chitosan, a linear polysaccharide composed of d-glucosamine residues and with a number of commercial and biomedical uses, had strong anti-bacteriophage effects, as demonstrated at in vitro and in vivo conditions. These findings bring promising perspectives for the prevention and treatment of haemolytic uremic syndrome (HUS) cases.

Enterotoxigenic Escherichia coli CS21 pilus contributes to adhesion to intestinal cells and to pathogenesis under in vivo conditions

Colonization surface antigens (CSs) represent key virulence-associated factors of enterotoxigenic Escherichia coli (ETEC) strains. They are required for gut colonization, the first step of the diarrhoeal disease process induced by these bacteria. One of the most prevalent CSs is CS21, or longus, a type IV pili associated with bacterial self-aggregation, protection against environmental stresses, biofilm formation and adherence to epithelial cell lines. The objectives of this study were to assess the role of CS21 in adherence to primary intestinal epithelial cells and to determine if CS21 contributes to the pathogenesis of ETEC infection in vivo. We evaluated adherence of a CS21-expressing wild-type ETEC strain and an isogenic CS21-mutant strain to pig-derived intestinal cell lines. To determine the role of CS21 in pathogenesis we used the above ETEC strains in a neonatal mice challenge infection model to assess mortality. Quantitative adherence assays confirmed that ETEC adheres to primary intestinal epithelial cells lines in a CS21-dependent manner. In addition, the CS21-mediated ETEC adherence to cells was specific as purified LngA protein, the CS21 major subunit, competed for binding with the CS21-expressing ETEC while specific anti-LngA antibodies blocked adhesion to intestinal cells. Neonatal DBA/2 mice died after intra-stomach administration of CS21-expressing strains while lack of CS21 expression drastically reduced the virulence of the wild-type ETEC strain in this animal model. Collectively these results further support the role of CS21 during ETEC infection and add new evidence on its in vivo relevance in pathogenesis.

The role of adjuvants in therapeutic protection against paracoccidioidomycosis after immunization with the P10 peptide

Paracoccidioidomycosis (PCM), a common chronic mycosis in Latin America, is a granulomatous systemic disease caused by the thermo-dimorphic fungus Paracoccidioides brasiliensis. The glycoprotein gp43 is the main antigen target of P. brasiliensis and a 15-mer internal peptide (QTLIAIHTLAIRYAN), known as P10, defines a major CD4(+)-specific T cell epitope. Previous results have indicated that, besides having a preventive role in conventional immunizations prior to challenge with the fungus, protective anti-fungal effects can be induced in P. brasiliensis-infected mice treated with P10 administered with complete Freund's adjuvant (CFA). The peptide elicits an IFN-γ-dependent Th1 immune response and is the main candidate for effective immunotherapy of patients with PCM, as an adjunctive approach to conventional chemotherapy. In the present study we tested the therapeutic effects of P10 combined with different adjuvants [aluminum hydroxide, CFA, flagellin, and the cationic lipid dioctadecyl-dimethylammonium bromide (DODAB)] in BALB/c mice previously infected with the P. brasiliensis Pb18 strain. Significant reductions in the number of colony forming units of the fungus were detected in lungs of mice immunized with P10 associated with the different adjuvants 52 days after infection. Mice treated with DODAB and P10, followed by mice treated with P10 and flagellin, showed the most prominent effects as demonstrated by the lowest numbers of viable yeast cells as well as reductions in granuloma formation and fibrosis. Concomitantly, secretion of IFN-γ and TNF-α, in contrast to interleukin (IL)-4 and IL-10, was enhanced in the lungs of mice immunized with P10 in combination with the tested adjuvants, with the best results observed in mice treated with P10 and DODAB. In conclusion, the present results demonstrate that the co-administration of the synthetic P10 peptide with several adjuvants, particularly DODAB, have significant therapeutic effects in experimental PCM.

Distribution and biological role of the oligopeptide-binding protein (OppA) in Xanthomonas species

In this study we investigated the prevalence of the oppA gene, encoding the oligopeptide binding protein (OppA) of the major bacterial oligopeptide uptake system (Opp), in different species of the genus Xanthomonas. The oppA gene was detected in two Xanthomonas axonopodis strains among eight tested Xanthomonas species. The generation of an isogenic oppA-knockout derivative of the Xac 306 strain, showed that the OppA protein neither plays a relevant role in oligopeptide uptake nor contributes to the infectivity and multiplication of the bacterial strain in leaves of sweet orange (Citrus sinensis) and Rangpur lime (Citrus limonia). Taken together these results suggest that the oppA gene has a recent evolutionary history in the genus and does not contribute in the physiology or pathogenesis of X. axonopodis.

Antibody responses elicited in mice immunized with Bacillus subtilis vaccine strains expressing Stx2B subunit of enterohaemorragic Escherichia coli O157:H7

No effective vaccine or immunotherapy is presently available for patients with the hemolytic uremic syndrome (HUS) induced by Shiga-like toxin (Stx) produced by enterohaemorragic Escherichia coli (EHEC) strains, such as those belonging to the O157:H7 serotype. In this work we evaluated the performance of Bacillus subtilis strains, a harmless spore former gram-positive bacterium species, as a vaccine vehicle for the expression of Stx2B subunit (Stx2B). A recombinant B. subtilis vaccine strain expressing Stx2B under the control of a stress inducible promoter was delivered to BALB/c mice via oral, nasal or subcutaneous routes using both vegetative cells and spores. Mice immunized with vegetative cells by the oral route developed low but specific anti-Stx2B serum IgG and fecal IgA responses while mice immunized with recombinant spores developed anti-Stx2B responses only after administration via the parenteral route. Nonetheless, serum anti-Stx2B antibodies raised in mice immunized with the recombinant B. subtilis strain did not inhibit the toxic effects of the native toxin, both under in vitro and in vivo conditions, suggesting that either the quantity or the quality of the induced immune response did not support an effective neutralization of Stx2 produced by EHEC strains.

Production of the refolded oligopeptide-binding protein (OppA) encoded by the citrus pathogen Xanthomonas axonopodis pv. Citri

The oligopeptide-binding protein, OppA, binds and ushers oligopeptide substrates to the membrane-associated oligopeptide permease (Opp), a multi-component ABC-type transporter involved in the uptake of oligopeptides expressed by several bacterial species. In the present study, we report the cloning, purification, refolding and conformational analysis of a recombinant OppA protein derived from Xanthomonas axonopodis pv. citri (X. citri), the etiological agent of citrus canker. The oppA gene was expressed in Escherichia coli BL21 (DE3) strain under optimized inducing conditions and the recombinant protein remained largely insoluble. Solubilization was achieved following refolding of the denatured protein. Circular dichroism analysis indicated that the recombinant OppA protein preserved conformational features of orthologs expressed by other bacterial species. The refolded recombinant OppA represents a useful tool for structural and functional analyses of the X. citri protein.

Structural model and ligand interactions of the Xanthomonas axonopodis pv. citri oligopeptide-binding protein

The oligopeptide-binding protein, OppA, ushers oligopeptide substrates to the membrane-associated oligopeptide permease (Opp), a multi-component ABC-type transporter involved in the uptake of oligopeptides by several bacterial species. In the present study, we report a structural model and an oligopeptide docking analysis of the OppA protein expressed by Xanthomonas axonopodis pv. citri (X. citri), the etiological agent of citrus canker. The X. citri OppA structural model showed a conserved three-dimensional structure, irrespective of the low amino acid identities with previously defined structures of Bacillus subtilis and Salmonella typhimurium orthologs. Oligopeptide docking analysis carried out with the proposed model indicated that the X. citri OppA preferentially binds tri- and tetrapeptides. The present study represents the first structural analysis of an OppA ortholog expressed by a phytopathogen and contributes to the understanding of the physiology and nutritional strategies of X. citri.

The oligopeptide (opp) gene cluster of Streptococcus mutans: identification, prevalence, and characterization

INTRODUCTION

The Opp system is an ATP-binding cassette-type transporter formed by membrane-associated proteins required for the uptake of oligopeptides in bacteria. In gram-positive bacteria, the Opp system, and particularly the oligopeptide-binding protein (OppA), has been shown to be involved in different aspects of cell physiology, including intercellular communication and binding to host proteins.

METHODS

In the present study we began to investigate the Opp system of Streptococcus mutans, the main etiological agent of dental caries.

RESULTS

Five opp genes (oppABCDF) organized in a single operon were identified in the genome of the S. mutans UA159 strain. Amino acid sequence analyses showed that the S. mutans OppA is closely related to an ortholog found in Streptococcus agalactiae. Incubation of S. mutans UA159 cells with an anti-OppA-specific serum did not inhibit biofilm formation on polystyrene plates. Moreover, S. mutans UA159 derivatives carrying deletions on the oppA or oppB genes did not show significant growth impairment, increased sensitivity to aminopterin, or defective capacity to form biofilms on polystyrene wells in the presence or not of saliva. Remarkably, only two out of three laboratory strains and one out of seven clinical strains recovered from tooth decay processes harbored a copy of the oppA gene and expressed the OppA protein.

CONCLUSION

Collectively, these results indicate that, in contrast to other Streptococcus species, the S. mutans Opp system, and particularly the OppA protein, does not represent an important trait required for growth and colonization.

Anti-tumor DNA vaccines based on the expression of human papillomavirus-16 E6/E7 oncoproteins genetically fused with the glycoprotein D from herpes simplex virus-1

DNA vaccines encoding the human papillomavirus type-16 (HPV-16) E6 and E7 oncoproteins genetically fused to the human herpes simplex virus type 1 (HSV-1) gD protein were tested in mice for induction of T cell-mediated immunity and protection against tumor cell challenge. Hybrid genes, generated after insertion of E6 or E7-encoding sequences into internal sites of the gD-encoding gene, were transcribed in vitro and the chimeric proteins were expressed at the surface of in vitro-transfected mammalian cells. Female C57BL/6 mice immunized with 4 intramuscular doses (100 microg of DNA/dose) of the DNA vaccines encoding E7 efficiently generated E7-specific CD8(+) T cells. Vaccination of mice with the DNA vaccines encoding the E7, or both E6 and E7, conferred complete protection to challenges from TC-1 tumor cells and partial therapeutic effect (40%) in mice inoculated with TC-1 cells on the same day or 5 days prior to the first vaccine dose.

Construction of plasmid-based expression vectors for Bacillus subtilis exhibiting full structural stability

A series of plasmid-based expression vectors have been constructed allowing stable intracellular expression of recombinant proteins in Bacillus subtilis strains. These expression vectors are based on the recently described Escherichia coli-B. subtilis shuttle vector pMTLBS72 which replicates as theta circles. Besides the weak constitutive promoter P(lepA), we inserted three different controllable promoters: P(gsiB) which can be induced by heat and acid shock, and by ethanol, P(xylA) and P(spac) which respond to the addition of xylose and IPTG, respectively. The versatility of these expression vectors was demonstrated by fusing their promoters to a reporter gene and by overexpression of the HtpG protein with three of them. All recombinant vectors exhibited full structural stability.

Prime-boost vaccine regimen confers protective immunity to human-derived enterotoxigenic Escherichia coli

Development of effective vaccines against diarrhea caused by enterotoxigenic Escherichia coli (ETEC) strains is still a priority for those living at or traveling to endemic regions. In this work, we evaluated the protective role of an anti-ETEC vaccine regimen based on parenteral priming with a DNA vaccine, pRECFA, followed by oral boosting with a recombinant attenuated Salmonella Typhimurium vaccine strain, HG3, both encoding the same antigen, the structural subunit (CfaB) of the ETEC CFA/I fimbriae. The DNA-priming Salmonella-boosting protocol enhanced both murine anti-CfaB serum IgG and fecal IgA antibody responses and increased the ability of serum antibodies to inhibit the adhesive properties of the CFA/I fimbriae expressed by live bacteria, as compared to mice immunized with only one vaccine type. Addition of a mucosal adjuvant (LTR192G) to the Salmonella vaccine strain further enhanced the synergic effects of the vaccine regimen on the induced CfaB-specific antibody responses. DBA/2 dams submitted to the prime-boost regimen transferred complete passive protection to suckling neonates challenged with a virulent ETEC strain. Detection of milk anti-CfaB IgA antibodies and protection conferred by vaccinated dams to neonates born from non-vaccinated dams indicated that secretion of antigen-specific IgA is the immune response induced by the protective vaccine regimen. These results demonstrate that priming with a DNA vaccine and boosting with a Salmonella strain enhances both quantitatively and qualitatively the antibody responses to the CfaB antigen and represents an alternative for either active or passive immunization approach to ETEC-associated diarrhea.

Combined vaccine regimen based on parenteral priming with a DNA vaccine and administration of an oral booster consisting of a recombinant Salmonella enterica serovar Typhimurium vaccine strain for immunization against infection with human-derived enterotoxigenic Escherichia coli strains

Repeated evidence has demonstrated that combined primer-booster immunization regimens can improve both secreted and humoral immune responses to antigens derived from viral, bacterial, and parasitic pathogens. For the present work, we evaluated the synergic serum immunoglobulin G (IgG) and fecal IgA antibody responses elicited in BALB/c mice who were intramuscularly primed with a DNA vaccine, pRECFA, followed by oral boosting with an attenuated Salmonella enterica serovar Typhimurium vaccine (HG3) strain, with both vaccines encoding the structural subunit (CfaB) of the CFA/I fimbriae produced by human-derived enterotoxigenic Escherichia coli (ETEC) strains. The immunological properties of the vaccine regimen were evaluated according to the order of the administered vaccines, the nature of the oral antigen carrier, the age of the vaccinated animals, the interval between the priming and boosting doses, and the amount of injected DNA. The production of gamma interferon and the IgG2a subclass in serum indicated that mice immunized with the primer-booster regimen developed prevailing type 1 T-cell-dependent immune responses. The synergic effect of the vaccine regimen on the induced antibody responses was also revealed by its ability to block the adhesive properties of CFA/I fimbriae expressed by live bacteria, as shown by the inhibition of Caco-2 cell and human erythrocyte binding. Moreover, DBA2 newborn mice were protected from lethal challenges with a CFA/I+ ETEC strain after the incubation of live bacteria with serum samples harvested from mice who were subjected to the primer-booster regimen. We propose, therefore, that the DNA primer-Salmonella booster regimen represents an alternative for the development of vaccines requiring both mucosal and systemic antibody responses for immunological protection.

Host and bacterial factors affecting induction of immune responses to flagellin expressed by attenuated Salmonella vaccine strains

Previous observations demonstrated that the delivery of recombinant Salmonella enterica serovar Dublin strains to mice via mucosal routes did not efficiently activate systemic and secreted antibody responses to either type d flagellin or genetically fused heterologous B-cell epitopes, thus reducing the usefulness of the protein as a carrier of epitopes for vaccine purposes. In this work, we investigated murine systemic and mucosal flagellin immunogenicity after oral immunization with attenuated Salmonella strains. The reduced anti-type d flagellin antibody responses in mice immunized via mucosal routes with three doses of flagellated S. enterica serovar Dublin strains were not caused by oral tolerance and could not be restored by coadministration of a mucosal adjuvant. The induction of antibody responses to Salmonella flagellins was shown to differ according to the genetic background, but not the haplotype, of the mouse lineage. Moreover, BALB/c mice orally immunized with S. enterica serovar Typhimurium strains developed anti-type i flagellin sera and secreted antibody responses, which indicated that the serovar of the Salmonella vaccine strain also affected flagellin immunogenicity. Analyses of cytokine responses of BALB/c mice immunized with three oral doses of flagellated S. enterica serovar Dublin vaccine strains showed that, in spite of the lack of antibody responses, elevated type d flagellin-specific CD4-cell-activation-dependent gamma interferon (IFN-gamma) and interleukin-10 responses were elicited after the administration of the vaccine strains via either parenteral or mucosal routes. Similar cytokine production patterns were detected to a T-cell heterologous epitope, derived from the CFA/I fimbriae of enterotoxigenic Escherichia coli (ETEC), in mice orally immunized with a Salmonella vaccine strain expressing hybrid flagella. These results indicate that the immunogenicities of Salmonella flagellins can differ significantly, depending on the murine host and on the bacterial vector used, and demonstrate that the induction of CD4-cell-activation-dependent IFN-gamma production represents a major immune response triggered by flagellin and in-frame fused heterologous T-cell epitopes after the oral administration of recombinant S. enterica serovar Dublin vaccine strains.

Altered expression of oligopeptide-binding protein (OppA) and aminoglycoside resistance in laboratory and clinical Escherichia coli strains

Oligopeptide-binding protein (OppA) is the periplasmic component of the major oligopeptide transport system of enteric bacteria. Genetic and biochemical evidence suggests that OppA plays a role in the uptake of aminoglycoside antibiotics in Escherichia coli K-12. Forty-six (82%) of 56 aminoglycoside-resistant mutants of E. coli K-12 selected in vitro had reduced or undetectable OppA levels, as compared with their parent strain. Moreover, nine (36%) of 25 aminoglycoside-resistant clinical isolates of E. coli expressed reduced or undetectable levels of OppA. No decrease in OppA expression was observed among aminoglycoside-sensitive E. coli strains from patients. Twenty-three (42%) of 56 aminoglycoside-resistant mutants of E. coli K-12 and six (24%) of 25 clinical isolates also were deficient for expression of ornithine or arginine decarboxylases, or both, and these deficiencies might negatively affect OppA expression by reducing polyamine synthesis. These results support the view that reduced OppA expression is associated with aminoglycoside resistance in E. coli strains.

Peptides 14VIDLL18 and 96FEAAAL101 defined as epitopes of antibodies raised against amino acid sequences of enterotoxigenic Escherichia coli colonization factor antigen I fused to Salmonella flagellin

Antibodies raised against four hybrid Salmonella flagellins carrying amino acid sequences derived from the fimbrial subunit of the colonization factor I antigen (CFA/I) of enterotoxigenic Escherichia coli (ETEC), i.e. hybrid flagellins Fla I (aa 1-15), Fla II (aa 11-25), Fla III (aa 32-45) and Fla IV (aa 88-102), were not able to inhibit the in vitro binding of CFA/I-expressing ETEC bacteria to enterocyte-like Caco-2 cells. However, one of the hybrid flagellins (Fla II) was recognized by a previously described anti-CFA/I subunit mAb (S-CFA/I 17:8) which was able to block adhesion of CFA/I-expressing bacteria to Caco-2 cells and to bind to the amino acid sequences 15IDLLQ19 of the CFA/I fimbrial subunit. Pepscan analysis of antibodies raised against the hybrid flagellins Fla II and Fla IV showed that they were specific for the sequences 14VIDLL18 and 96FEAAAL101, respectively, of the CFA/I fimbrial subunit. Thus, the discrepancy in the abilities of the anti-Fla II serum and the mAb S-CFA/I 17:8 to block binding might be ascribed to their slightly different fine specificity for epitopes.