Determination of the optimal route of administration of Salmonella typhimurium A1-R to target breast cancer in nude mice

We have developed the genetically-modified Salmonella typhimurium A1-R strain that selectively targets tumors. S. typhimurium A1-R is auxotrophic for Leu and Arg, which precludes it from growing continuously in normal tissues but allows high tumor virulence. We report here the efficacy and safety of three different routes of S. typhimurium A1-R administration: oral (p.o.), intravenous (i.v.), and intra-tumoral (i.t.) in nude mice with orthotopic human breast cancer. Nude mice with MDA-MB-435 human breast cancer, expressing red fluorescent protein (RFP), were administered S. typhimurium A1-R by one of the three routes: [p.o.: 2×10(8) colony forming units (CFU)/200 μl; i.v.: 2.5×10(7) CFU/100 μl; i.t.: 2.5×10(7) CFU/50 μl] twice a week. Tumor growth was monitored by fluorescence imaging and caliper measurement in two dimensions. S. typhimurium A1-R targeted tumors at much higher levels than normal organs after all three routes of administration. The fewest bacteria were detected in normal organs after p.o. administration, which suggests that p.o. administration has the highest safety. The i.v. route had the greatest antitumor efficacy. There were no obvious toxic effects on the host with any of the routes of administration. The results of this study suggest that p.o. administration was the most safe to the host and the i.v. route was most effective for tumor targeting with S. typhimurium A1-R.

Variable carbon catabolism among Salmonella enterica serovar Typhi isolates

Background

Salmonella enterica serovar Typhi (S. Typhi) is strictly a human intracellular pathogen. It causes acute systemic (typhoid fever) and chronic infections that result in long-term asymptomatic human carriage. S. Typhi displays diverse disease manifestations in human infection and exhibits high clonality. The principal factors underlying the unique lifestyle of S. Typhi in its human host during acute and chronic infections remain largely unknown and are therefore the main objective of this study.

Methodology/Principal Findings

To obtain insight into the intracellular lifestyle of S. Typhi, a high-throughput phenotypic microarray was employed to characterise the catabolic capacity of 190 carbon sources in S. Typhi strains. The success of this study lies in the carefully selected library of S. Typhi strains, including strains from two geographically distinct areas oftyphoid endemicity, an asymptomatic human carrier, clinical stools and blood samples and sewage-contaminated rivers. An extremely low carbon catabolic capacity (27% of 190 carbon substrates) was observed among the strains. The carbon catabolic profiles appeared to suggest that S. Typhi strains survived well on carbon subtrates that are found abundantly in the human body but not in others. The strains could not utilise plant-associated carbon substrates. In addition, α-glycerolphosphate, glycerol, L-serine, pyruvate and lactate served as better carbon sources to monosaccharides in the S. Typhi strains tested.

Conclusion

The carbon catabolic profiles suggest that S. Typhi could survive and persist well in the nutrient depleted metabolic niches in the human host but not in the environment outside of the host. These findings serve as caveats for future studies to understand how carbon catabolism relates to the pathogenesis and transmission of this pathogen.

Cloning, protein expression and display of synthetic multi-epitope mycobacterial antigens on Salmonella typhi Ty21a cell surface

Expressing proteins of interest as fusion to proteins of bacterial envelope is a powerful technique for biotechnological and medical applications. The synthetic gene (VacII) encoding for T-cell epitopes of selected genes of Mycobacterium tuberculosis namely, ESAT6, MTP40, 38 kDa, and MPT64 was fused with N- terminus of Pseudomonas syringae ice nucleation protein (INP) outer membrane protein. The fused genes were cloned into a bacterial expression vector pKK223-3. The recombinant protein was purified by Ni-NAT column. VacII gene was displayed on the cell surface of Salmonella typhi Ty21a using N-terminal region of ice nucleation proteins (INP) as an anchoring motif. Glycine method confirmed that VacII was anchored on the cell surface. Western blot analysis further identified the synthesis of INP derivatives containing the N-terminal domain INP- VacII fusion protein of the expected size (52 kDa).

TolA mediates the differential detergent resistance pattern between the Salmonella enterica subsp. enterica serovars Typhi and Typhimurium

The tol-pal genes are essential for maintaining the outer membrane integrity and detergent resistance in various Gram-negative bacteria, including Salmonella. The role of TolA has been well established for the bile resistance of Salmonella enterica subsp. enterica serovar Typhimurium. We compared the bile resistance pattern between the S. enterica serovars Typhi and Typhimurium and observed that Typhi is more resistant to bile-mediated damage. A closer look revealed a significant difference in the TolA sequence between the two serovars which contributes to the differential detergent resistance. The tolA knockout of both the serovars behaves completely differently in terms of membrane organization and morphology. The role of the Pal proteins and difference in LPS organization between the two serovars were verified and were found to have no direct connection with the altered bile resistance. In normal Luria broth (LB), S. Typhi ΔtolA is filamentous while S. Typhimurium ΔtolA grows as single cells, similar to the wild-type. In low osmolarity LB, however, S. Typhimurium ΔtolA started chaining and S. Typhi ΔtolA showed no growth. Further investigation revealed that the chaining phenomenon observed was the result of failure of the outer membrane to separate in the dividing cells. Taken together, the results substantiate the evolution of a shorter TolA in S. Typhi to counteract high bile concentrations, at the cost of lower osmotic tolerance.

Occurrence & antibiogram of Salmonella Typhi & S. Paratyphi A isolated from Rourkela, Orissa

BACKGROUND & OBJECTIVES

Almost round-the-year occurrence of Salmonella Typhi and Salmonella Paratyphi A has been noticed in Rourkela since last 13 and five years respectively. The incidence of infection along with the antibiogram of these two serotypes in this area were carried out.

METHODS

The study was carried out at Ispat General Hospital, Rourkela, India, between January 2005 and December 2008 with 5340 blood samples collected from patients with suspected enteric fever and pyrexia of unknown origin. Isolation, identification and antibiogram of the causative organisms were performed according to standard bacteriological procedures.

RESULTS

A total of 298 Salmonella isolates showed an overall per cent positivity of 5.58. Multidrug resistance was found in 11.96 per cent and 15.62 per cent isolates of S. Typhi and S. Paratyphi A respectively. Less than 2 per cent isolates of Salmonella showed resistance to ciprofloxacin. A resistance of 3.0 to 6.25 per cent against third generation cephalosporins was observed among the salmonella isolates.

INTERPRETATION & CONCLUSION

A round-the-year occurrence of Salmonella spp. in Rourkela might have been due to the presence of a considerable number of carriers in the locality, poor sanitation in nearby slum areas, and inadequate and contaminated community water supply at times. Higher degree of susceptibility among S. Typhi isolates against various antibiotics was encouraging, but increasing trend of resistance observed among S. Paratyphi A isolates was a matter of concern.

Effects of two different dosing regimens of terlipressin on organ functions in ovine endotoxemia

OBJECTIVE AND DESIGN

To test the hypothesis that a continuous infusion of the vasopressin analog terlipressin is associated with less organ dysfunction as compared to intermittent bolus infusion in an ovine sepsis model.

SUBJECTS

Twenty-seven adult female sheep.

TREATMENT

All sheep were subjected to a Salmonella typhosa endotoxin infusion (10 ng/kg/min). After 16 h of endotoxemia, the surviving animals (n = 24) were randomized to (1) an untreated control group, (2) a continuous terlipressin group (2 mg/24 h), or (3) a terlipressin bolus group (1 mg/6 h).

METHODS

Hemodynamic variables were measured and blood was withdrawn at specific time points for the assessment of organ functions.

RESULTS

Continuous terlipressin infusion was associated with improved surrogate parameters of myocardial, renal, and hepatic function as compared with terlipressin bolus infusion. Reduced vascular hyperpermeability was evidenced by an attenuated decrease in plasma protein concentrations in sheep treated with continuous terlipressin infusion as compared to bolus injection or no treatment.

CONCLUSIONS

Continuous infusion of low-dose terlipressin preserved several surrogate parameters of organ function better than intermittent bolus injections in sheep with systemic inflammation.

Comparative proteomic analysis of the PhoP regulon in Salmonella enterica serovar Typhi versus Typhimurium

Background

S. Typhi, a human-restricted Salmonella enterica serovar, causes a systemic intracellular infection in humans (typhoid fever). In comparison, S. Typhimurium causes gastroenteritis in humans, but causes a systemic typhoidal illness in mice. The PhoP regulon is a well studied two component (PhoP/Q) coordinately regulated network of genes whose expression is required for intracellular survival of S. enterica.

Methodology/Principal Findings

Using high performance liquid chromatography mass spectrometry (HPLC-MS/MS), we examined the protein expression profiles of three sequenced S. enterica strains: S. Typhimurium LT2, S. Typhi CT18, and S. Typhi Ty2 in PhoP-inducing and non-inducing conditions in vitro and compared these results to profiles of phoP⁻/Q⁻ mutants derived from S. Typhimurium LT2 and S. Typhi Ty2. Our analysis identified 53 proteins in S. Typhimurium LT2 and 56 proteins in S. Typhi that were regulated in a PhoP-dependent manner. As expected, many proteins identified in S. Typhi demonstrated concordant differential expression with a homologous protein in S. Typhimurium. However, three proteins (HlyE, STY1499, and CdtB) had no homolog in S. Typhimurium. HlyE is a pore-forming toxin. STY1499 encodes a stably expressed protein of unknown function transcribed in the same operon as HlyE. CdtB is a cytolethal distending toxin associated with DNA damage, cell cycle arrest, and cellular distension. Gene expression studies confirmed up-regulation of mRNA of HlyE, STY1499, and CdtB in S. Typhi in PhoP-inducing conditions.

Conclusions/Significance

This study is the first protein expression study of the PhoP virulence associated regulon using strains of Salmonella mutant in PhoP, has identified three Typhi-unique proteins (CdtB, HlyE and STY1499) that are not present in the genome of the wide host-range Typhimurium, and includes the first protein expression profiling of a live attenuated bacterial vaccine studied in humans (Ty800).

Priming of Salmonella enterica serovar typhi-specific CD8(+) T cells by suicide dendritic cell cross-presentation in humans

BACKGROUND

The emergence of antibiotic-resistant strains of Salmonella enterica serovar Typhi (S. Typhi), the etiologic agent of typhoid fever, has aggravated an already important public health problem and added new urgency to the development of more effective typhoid vaccines. To this end it is critical to better understand the induction of immunity to S. Typhi. CD8(+) T cells are likely to play an important role in host defense against S. Typhi by several effector mechanisms, including killing of infected cells and IFN-gamma secretion. However, how S. Typhi regulates the development of specific CD8(+) responses in humans remains unclear. Recent studies in mice have shown that dendritic cells (DC) can either directly (upon uptake and processing of Salmonella) or indirectly (by bystander mechanisms) elicit Salmonella-specific CD8(+) T cells.

METHODOLOGY/PRINCIPAL FINDINGS

We report here that upon infection with live S. Typhi, human DC produced high levels of pro-inflammatory cytokines IL-6, IL-8 and TNF-alpha, but low levels of IL-12 p70 and IFN-gamma. In contrast, DC co-cultured with S. Typhi-infected cells, through suicide cross-presentation, uptake S. Typhi-infected human cells and release high levels of IFN-gamma and IL-12p70, leading to the subsequent presentation of bacterial antigens and triggering the induction of memory T cells, mostly CD3(+)CD8(+)CD45RA(-)CD62L(-) effector/memory T cells.

CONCLUSIONS/SIGNIFICANCE

This study is the first to demonstrate the effect of S. Typhi on human DC maturation and on their ability to prime CD8(+) cells and highlights the significance of these phenomena in eliciting adaptive immunity to S. Typhi.

Characterization of MgtC, a virulence factor of Salmonella enterica Serovar Typhi

The MgtC is a virulence factor in Salmonella Typhimurium that is required for growth at low-Mg2+ concentrations and intramacrophage survival. This gene is codified in a conserved region of the Salmonella pathogenicity island 3 (SPI-3), and is also present in the chromosome of other Salmonella serovars. In this study we characterized the MgtC factor in S. Typhi, a human specific pathogen, by using mgtC and SPI-3 mutant strains. We found that MgtC is the most important factor codified in the SPI-3 of S. Typhi for growth in low-Mg2+ media and survival within human cells. In addition, by using reporter genes we determined that the low-Mg2+ concentration, acidic media and PhoP regulator induce mgtC expression in S. Typhi. We suggest that MgtC is the most important virulence factor codified in the SPI-3 of S. Typhi.

A sensitive liquid chromatography/mass spectrometry-based assay for quantitation of amino-containing moieties in lipid A

A novel sensitive liquid chromatography/mass spectrometry-based assay was developed for the quantitation of aminosugars, including 2-amino-2-deoxyglucose (glucosamine, GlcN), 2-amino-2-deoxygalactose (galactosamine, GalN), and 4-amino-4-deoxyarabinose (aminoarabinose, AraN), and for ethanolamine (EtN), present in lipid A. This assay enables the identification and quantitation of all amino-containing moieties present in lipopolysaccharide or lipid A from a single sample. The method was applied to the analysis of lipid A (endotoxin) isolated from a variety of biosynthetic and regulatory mutants of Salmonella enterica serovar Typhimurium and Francisella tularensis subspecies novicida. Lipid A is treated with trifluoroacetic acid to liberate and deacetylate individual aminosugars and mass tagged with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate, which reacts with primary and secondary amines. The derivatives are separated using reversed-phase chromatography and analyzed using a single quadrupole mass spectrometer to detect quantities as small as 20 fmol. GalN was detected only in Francisella and AraN only in Salmonella, while GlcN was detected in lipid A samples from both species of bacteria. Additionally, we found an approximately 10-fold increase in the level of AraN in lipid A isolated from Salmonella grown in magnesium-limited versus magnesium-replete conditions. Salmonella with defined mutations in lipid A synthesis and regulatory genes were used to further validate the assay. Salmonella with null mutations in the phoP, pmrE, and prmF genes were unable to add AraN to their lipid A, while Salmonella with constitutively active phoP and pmrA exhibited AraN modification of lipid A even in the normally repressive magnesium-replete growth condition. The described assay produces excellent repeatability and reproducibility for the detection of amino-containing moieties in lipid A from a variety of bacterial sources.

Regulation of Vi capsular polysaccharide synthesis in Salmonella enterica serotype Typhi

The synthesis of Vi polysaccharide, a major virulence determinant in Salmonella enterica serotype Typhi (S. Typhi), is under the control of two regulatory systems, ompR-envZ and rscB-rscC, which respond to changes in osmolarity. Some S. Typhi isolates exhibit over-expression of Vi polysaccharide, which masks clinical detection of LPS O-antigen. This variation in Vi polysaccharide and O-antigen display (VW variation) has been observed since the initial studies of S. Typhi. We have reported that the status of the rpoS gene is responsible for this phenomenon. We review the regulatory network of the Vi polysaccharide, linking osmolarity and RpoS expression. Also, we discuss how this may impact live attenuated Salmonella vaccine development.

Synthesis, spectroscopic and biological aspects of iron(II) complexes

Five novel coordinated complexes of iron(II) with ciprofloxacin and neutral bidentate ligands have been prepared and characterized using elemental analyses, magnetic measurements, IR spectra, UV-VIS spectral, thermogravimetric analyses, 1H-NMR and 13C-NMR. The antimicrobial activity of the individual ligands, metal salt and metal complexes with respect to Bacillus subtilis, Escherichia coli, Bacillus cereus, Staphylococcus aureus, Salmonella typhi, Serratia marcescens, Aspergillus niger, Aspergillus flavus and Lasiodiplodia theobromae were evaluated by the agar-plate technique in comparison to reference standard drugs (ofloxacin, levofloxacin and fluconozole). Binding of the complexes to DNA was studied and is discussed.

Synthesis, spectral, catalytic and antimicrobial studies of PPh3/AsPh3 complexes of Ru(II) with dibasic tridentate O, N, S donor ligands

Complexes of the type [Ru(CO)(EPh(3))(B)(L)] (E = P or As; B = PPh(3), AsPh(3), py or pip; L=dianion of the Schiff bases derived from thiosemicarbazone with acetoacetanilide, acetoacet-o-toluidide and o-chloro acetoacetanilide) have been synthesized from the reactions of equimolar amounts of [RuHCl(CO)(EPh(3))(2)(B)] and Schiff bases in benzene. The new complexes have been characterized by analytical and spectral (IR, electronic, NMR) data. The arrangement of PPh(3) groups around ruthenium metal was determined from (31)P NMR spectra. An octahedral structure has been assigned for all the new complexes. All the complexes exhibited catalytic activity for the oxidation of benzyl alcohol and cyclohexanol in presence of N-methylmorpholine-N-oxide as co-oxidant. The complexes also exhibited antibacterial activity against E. coli, Aeromonas hydrophilla and Salmonella typhi. The activity was compared with standard streptomycin.

Dissecting the Salmonella response to copper

Intracellular copper homeostasis in bacteria is maintained as the result of a complex ensemble of cellular processes that in Escherichia coli involve the coordinated action of two systems, cue and cus. In contrast, the pathogenic bacterium Salmonella harbours only the cue regulon, including copA, which is shown here to be transcriptionally controlled by CueR. Mutant strains in the CueR-regulated genes were constructed to characterize the response of Salmonella enterica serovar Typhimurium to high concentrations of extracellular copper under both aerobic and anaerobic conditions. Unlike its counterpart in E. coli, inactivation of cuiD displays the most severe phenotype and is also required for copper tolerance under anaerobic conditions. Deletion of copA has a mild effect in aerobiosis, but strongly impairs survival in the absence of oxygen. In a DeltacopA strain, a second Salmonella-specific P-type ATPase, GolT, can substitute the copper transporter, diminishing the effect of its deletion. The overall results highlight the importance of the cue system for controlling intracellular copper stress. The observed differences between Salmonella and E. coli in handling copper excess may contribute to our understanding of the distinct capability of these related pathogenic bacteria to survive outside the host.

Identification of a transcriptional regulator that controls intracellular gene expression in Salmonella Typhi

Salmonella enterica serovar Typhi (S. Typhi), the aetiological agent of typhoid fever, is an exclusively human pathogen. Little is known about specific factors that may confer to this bacterium its unique pathogenic features. One of these determinants is CdtB, a homologue of the active subunit of the cytolethal distending toxin, which causes DNA damage leading to cell cycle arrest and distension of intoxicated cells. A unique property of S. Typhi CdtB is that it is only synthesized when this bacterium is within an intracellular compartment. Through a genetic screen, we have identified a transcriptional regulatory protein that controls the intracellular expression of cdtB. This regulator, which we have named IgeR, is a member of the DeoR family of transcriptional regulatory proteins and is highly conserved in all S. enterica serovars. IgeR directly binds the cdtB promoter and represses its expression in the extracellular environment. Microarray analysis identified additional IgeR-regulated genes that are involved in virulence. Constitutive expression of igeR resulted in the reduction of intracellular expression of cdtB by S. Typhi and in significant impairment of the virulence of Salmonella enterica serovar Typhimurium (S. Typhimurium) in mice. We propose that IgeR may co-ordinate gene expression during Salmonella's transition from an extracellular to an intracellular environment.

Type IVB pilus operon promoter controlling expression of the severe acute respiratory syndrome-associated coronavirus nucleocapsid gene in Salmonella enterica Serovar Typhi elicits full immune response by intranasal vaccination

Attenuated Salmonella enterica serovar Typhi strains have been considered to be attractive as potential live oral delivery vector vaccines because of their ability to elicit the full array of immune responses in humans. In this study, we constructed an attenuated S. enterica serovar Typhi strain stably expressing conserved nucleocapsid (N) protein of severe acute respiratory syndrome-associated coronavirus (SARS-CoV) by integrating the N gene into the pilV gene, which was under the control of the type IVB pilus operon promoter in S. enterica serovar Typhi. BALB/c mice were immunized with this recombinant strain through different routes: intranasally, orogastrically, intraperitoneally, and intravenously. Results showed that the intranasal route caused the highest production of specific immunoglobulin G (IgG), IgG2a, and secretory IgA, where IgG2a was imprinted as a Th1 cell bias. Moreover, this recombinant live vaccine induced significantly high levels of specific cytotoxic T-lymphocyte activities and increased gamma interferon-producing T cells compared with the parental strain. Our work provides insights into how the type IVB pilus operon promoter controlling SARS-CoV N gene expression in Salmonella might be attractive for a live-vector vaccine against SRAS-CoV infection, for it could induce mucosal, humoral, and cellular immune responses. Our work also indicates that the type IVB pilus operon promoter controlling foreign gene expression in Salmonella can elicit full immune responses by intranasal vaccination.

[Characterization of two typhoid fever outbreaks in Apartadó, Antioquia, 2005]

INTRODUCTION

The characterization of typhoid fever outbreaks is important because it is necessary to find the source of the infection and development control measures.

OBJECTIVE

A typhoid fever outbreak is described from Apartadó and the Salmonella Typhi isolates characterized by phenotypic and genotypic methods.

MATERIALS AND METHODS

From 44 patients, 15 blood cultures and 7 stools cultures were recovered. Phenotypic identification of isolates was done by biochemical and serological tests, and antibiotic susceptibility was tested. Genes hilA, invA and the IS200 marker were evaluated by polymerase chain reaction; pulsed field gel electrophoresis was used for the XbaI gene. Eight water samples were examined by polymerase chain reaction and culture methods in order to isolate Salmonella spp.

RESULTS

Fifteen patients were confirmed for typhoid fever, 13 by blood cultures and two by stools cultures. All S. Typhi isolates were susceptible to the antimicrobials tested. The presence of hilA, invA and IS200 were confirmed by polymerase chain reaction in all isolates. The pulsed field gel electrophoresis method grouped 10 isolates in COINJPP.X01.0035 pattern, three in COINJPPX01.0002, one in COINJPP.X01.0012 and one in COINJPPX01.0037. Water isolates were negatives for Salmonella spp.

CONCLUSIONS

Pulsed field gel electrophoresis discriminated the isolates in two outbreaks. Initially the cases were described as only one outbreak, by epidemiological criteria and phenotypic test. Additionally two isolates with different clonal origin were discriminated, indicating that they were unrelated to the other cases. It was not possible to confirm the infection source from water samples.

Effects of thoracic epidural anesthesia on hemodynamics and global oxygen transport in ovine endotoxemia

Besides providing effective analgesia, thoracic epidural anesthesia (TEA) has been shown to decrease perioperative morbidity and mortality. Because of its vasodilatory properties in association with the sympathetic blockade, however, TEA may potentially aggravate cardiovascular dysfunctions resulting from sepsis and systemic inflammatory response syndrome. The objective of the present study was to assess the effects of TEA on hemodynamics, global oxygen transport, and renal function in ovine endotoxemia. After a baseline measurement in healthy sheep (n = 18), Salmonella typhosa endotoxin was centrally infused at incremental doses to induce and maintain a hypotensive-hypodynamic circulation using an established protocol. The animals were then randomly assigned to one of two groups. In the treatment group, continuous TEA was initiated with 0.1 mL.kg of 0.125% bupivacaine at the onset of endotoxemia and maintained with 0.1 mL.kg.h. In the control group, the same amount of isotonic sodium chloride solution was injected through the epidural catheter. In the animals surviving the entire experiment (n = 7 per group), cardiac index and mean arterial pressure decreased in a dose-dependent manner during endotoxin infusion. In the TEA group, neither systemic hemodynamics nor global oxygen transport were impaired beyond the changes caused by endotoxemia itself. Urinary output was increased in the TEA group as compared with the control group (P < 0.05). In this model of endotoxic shock, TEA improved renal perfusion without affecting cardiopulmonary hemodynamics and global oxygen transport.

Functional changes of macrophages induced by dimeric glycosaminylmuramyl pentapeptide

Under the influence of dimeric glucosaminylmuramyl pentapeptide (diGMPP), a component of bacterial cell wall, macrophages undergo certain changes similar to those associated with dendritic cell (DC) maturation. The effect of diGMPP on DCs resulted in maturation and expression of CD83. Macrophages treated with diGMPP displayed reduced phagocytic activity and elevated ability to kill ingested bacteria. Reduced phagocytosis may be due to phenotypic changes that occur in macrophages during the maturation process, such as reduced expression of receptors that mediate ingesting of microorganisms (CD16, CD64, and CD11b). Down-regulated expression of pattern-recognizing receptors (TLR2, TLR4, and CD206) was accompanied by elevated expression of antigen-presenting (HLA-DR) and costimulating molecules (CD86 and CD40), similar to alterations observed in maturating DCs. In addition, diGMPP treatment of macrophages resulted in enhanced synthesis of IL-12, TNF-alpha, and IL-1beta.

Role of RpoS in fine-tuning the synthesis of Vi capsular polysaccharide in Salmonella enterica serotype Typhi

Regulation of the synthesis of Vi polysaccharide, a major virulence determinant in Salmonella enterica serotype Typhi, is under the control of two regulatory systems, ompR-envZ and rscB-rscC, which respond to changes in osmolarity. Some serotype Typhi strains exhibit overexpression of Vi polysaccharide, which masks clinical detection of lipopolysaccharide O antigen. This variation in Vi polysaccharide and O antigen display (VW variation) has been observed since the initial studies of serotype Typhi. In this study, we report that rpoS plays a role in this increased expression in Vi polysaccharide. We constructed a variety of isogenic serotype Typhi mutants that differed in their expression levels of RpoS and examined the role of the rpoS product in synthesis of Vi polysaccharide under different osmolarity conditions. Vi polysaccharide synthesis was also examined in serotype Typhi mutants in which the native promoter of the rpoS was replaced by an araCP(BAD) cassette, so that the expression of rpoS was arabinose dependent. The RpoS(-) strains showed increased syntheses of Vi polysaccharide, which at low and medium osmolarities masked O antigen detection. In contrast, RpoS(+) strains showed lower syntheses of Vi polysaccharide, and an increased detection of O antigen was observed. During exponential growth, when rpoS is unstable or present at low levels, serotype Typhi RpoS(+) strains overexpress the Vi polysaccharide at levels comparable to those for RpoS(-) strains. Our results show that RpoS is another regulator of Vi polysaccharide synthesis and contributes to VW variation in serotype Typhi, which has implications for the development of recombinant attenuated Salmonella vaccines in humans.

The Salmonella enterica serovar Typhi type IVB self-association pili are detached from the bacterial cell by the PilV minor pilus proteins

Salmonella enterica serovar Typhi and some strains (Vi+) of serovar Dublin use type IVB pili to facilitate bacterial self-association, but only when the PilV proteins (potential minor pilus proteins) are not synthesized. Pilus-mediated self-association may be important in the pathogenesis of enteric fever. We have shown previously that the extent of DNA supercoiling controls the rate of Rci-catalyzed inversion of a DNA fragment which includes the C-terminal portions of the PilV proteins. This inversion therefore controls PilV synthesis as a high inversion rate prohibits transcription of pilV-encoding DNA. Here, we describe the manner in which PilV protein expression inhibits bacterial self-association and present data which suggest that incorporation of one or a few PilV protein molecules into a growing pilus, comprised of PilS subunits, causes the pilus to detach at the bacterial membrane. The bacteria are then unable to self-associate. We suggest that this phenomenon may be relevant to the pathogenesis of typhoid fever.

Involvement of caspase-3, lipid peroxidation and TNF-alpha in causing apoptosis of macrophages by coordinately expressed Salmonella phenotype under stress conditions

Invasive Salmonella has been reported to induce apoptosis of macrophages as a part of its infection process, which may allow it to avoid detection by the innate immune system. However, the bacterial components capable of inducing apoptosis, particularly under the environments offered by the host have not been fully identified. Therefore, in the present study, attempts were made to evaluate the apoptotic potential of Salmonella enterica serovar Typhi (S. typhi) outer membrane protein expressed under stress conditions like iron, oxidative and anaerobic simulating the in vivo situations encountered by the pathogen. Analysis of data revealed that a coordinately expressed 69kDa outer membrane protein (OMP) expressed with enhanced intensity under iron, oxidative and anaerobic stress conditions caused apoptotic cell death in 51% of macrophages, whereas OMPs of S. typhi extracted under normal conditions accounted for apoptotic cell death in only 31% of macrophages. A significantly enhanced activity of caspase-3 was observed during macrophage-apoptosis induced by this protein. A significant increase in the extent of lipid peroxidation (levels of oxidant) and decrease in the activities of antioxidants was also observed which correlated with the increased generation of tumor necrosis factor-alpha, interleukine-1alpha and interleukine-6. These results suggest that caspase-3 and tumor necrosis factor-alpha in conjunction with other cytokines may induce apoptotic cell death through the up-regulation of oxidants and down-regulation of antioxidants. These findings may be relevant for the better understanding of the disease pathophysiology and for the future developments of diagnostic and preventive strategies during the host-pathogen interactions.

Tumour necrosis factor alpha mediated apoptosis in murine macrophages by Salmonella enterica serovar Typhi under oxidative stress

Invasive Salmonella has been reported to induce apoptosis of macrophages as part of its infection process, which may allow it to avoid detection by the innate immune system. However, the induction of apoptosis under the different host environments remains to be examined, including the oxidative stress experienced by pathogens in the macrophage milieu. To simulate in vivo oxidative conditions, Salmonella enterica serovar Typhi was grown in the presence of hydrogen peroxide and its ability to induce apoptosis of murine macrophages was assessed. Analysis of data revealed that oxidative stressed S. Typhi caused apoptotic cell death in 51% of macrophages, whereas S. Typhi grown under normal conditions accounted for apoptotic cell death in only 32% of macrophages. A significant increase in the levels of oxidants and decrease in the antioxidant was also observed which correlated with the increased generation of tumour necrosis factor alpha, interleukin-1alpha and interleukin-6. These results suggest that tumour necrosis factor alpha in conjunction with other cytokines may induce apoptotic cell death through the up-regulation of lipid peroxidation and down-regulation of superoxide dismutase. This finding may help us to understand better the host-pathogen interactions and may be of clinical importance in the development of preventive intervention against infection.

The MgtC virulence factor of Salmonella enterica serovar Typhimurium activates Na(+),K(+)-ATPase

The mgtC gene of Salmonella enterica serovar Typhimurium encodes a membrane protein of unknown function that is important for full virulence in the mouse. Since mgtC is part of an operon with mgtB which encodes a Mg(2+)-transporting P-type ATPase, MgtC was hypothesized to function in ion transport, possibly in Mg(2+) transport. Consequently, MgtC was expressed in Xenopus laevis oocytes, and its effect on ion transport was evaluated using ion selective electrodes. Oocytes expressing MgtC did not exhibit altered currents or membrane potentials in response to changes in extracellular H(+), Mg(2+), or Ca(2+), thus ruling out a previously postulated function as a Mg(2+)/H(+) antiporter. However, addition of extracellular K(+) markedly hyperpolarized membrane potential instead of the expected depolarization. Addition of ouabain to block the oocyte Na(+),K(+)-ATPase completely prevented hyperpolarization and restored the normal K(+)-induced depolarization response. These results suggested that the Na(+),K(+)-ATPase was constitutively activated in the presence of MgtC resulting in a membrane potential largely dependent on Na(+),K(+)-ATPase. Consistent with the involvement of Na(+),K(+)-ATPase, oocytes expressing MgtC exhibited an increased rate of (86)Rb(+) uptake and had increased intracellular free [K(+)] and decreased free [Na(+)] and ATP. The free concentrations of Mg(2+) and Ca(2+) and cytosolic pH were unchanged, although the total intracellular Ca(2+) content was slightly elevated. These results suggest that the serovar Typhimurium MgtC protein may be involved in regulating membrane potential but does not directly transport Mg(2+) or another ion.

Vi antigen biosynthesis in Salmonella typhi: characterization of UDP-N-acetylglucosamine C-6 dehydrogenase (TviB) and UDP-N-acetylglucosaminuronic acid C-4 epimerase (TviC)

Vi antigen, the virulence factor of Salmonella typhi, has been used clinically as a molecular vaccine. TviB and TviC are two enzymes involved in the formation of Vi antigen, a linear polymer consisting of alpha-1,4-linked N-acetylgalactosaminuronate. Protein sequence analysis suggests that TviB is a dehydrogenase and TviC is an epimerase. Both enzymes are expected to be NAD(+) dependent. In order to verify their functions, TviB and TviC were cloned, expressed in Escherichia coli, and characterized. The C-terminal His(6)-tagged TviB protein, purified from soluble cell fractions in the presence of 10 mM DTT, shows UDP-N-acetylglucosamine 6-dehydrogenase activity and is capable of catalyzing the conversion of UDP-N-acetylglucosamine (UDP-GlcNAc) to UDP-N-acetylglucosaminuronic acid (UDP-GlcNAcA) with a k(cat) value of 15.5 +/- 1.0 min(-)(1). The K(m) values of TviB for UDP-GlcNAc and NAD(+) are 77 +/- 9 microM and 276 +/- 52 microM, respectively. TviC, purified as C-terminal hexahistidine-tagged protein, shows UDP-GlcNAcA 4-epimerase and UDP-N-acetylgalactosamine (UDP-GalNAc) 4-epimerase activities. The K(m) values of TviC for UDP-GlcNAcA and UDP-N-acetylgalactosaminuronic acid (UDP-GalNAcA) are 20 +/- 1 microM and 42 +/- 2 microM, respectively. The k(cat) value for the conversion of UDP-GlcNAcA to UDP-GalNAcA is 56.8 +/- 0.5 min(-)(1), while that for the reverse reaction is 39.1 +/- 0.6 min(-)(1). These results show that the biosynthesis of Vi antigen is initiated by the TviB-catalyzed oxidation of UDP-GlcNAc to UDP-GalNAc, followed by the TviC-catalyzed epimerization at C-4 to form UDP-GalNAcA, which serves as the building block for the formation of Vi polymer. These results set the stage for future in vitro biosynthesis of Vi antigen. These enzymes may also be drug targets to inhibit Vi antigen production.