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R Curtiss

Publications and source records attributed to R Curtiss.

At least 19 recordsLinked to original sources
PubMed2001

Intranasal immunogenicity of a Delta cya Delta crp-pabA mutant of Salmonella enterica serotype Typhimurium for the horse.

The aim of this study was to investigate the intranasal immunogenicity for the horse of a Deltacya Deltacrp-pabA mutant (MGN-707) of Salmonella enterica serotype Typhimurium (S. typhimurium). MGN-707 caused no sign of disease, was not detected in feces and a single administration induced strong Salmonella-specific serum and nasal mucosal antibody responses. All ponies had made strong salmonella specific serum IgGa, IgGb, IgA and IgM antibody responses by day 25 after the first immunization. IgM responses to salmonella lipopolysaccharide (LPS) were short lived whereas salmonella specific serum IgGa and IgGb persisted at high levels in all ponies until 83 and 140 days, respectively. Specific nasal mucosal antibody responses dominated by IgA and IgM were evident by day 25 in all ponies except one in which only specific IgGa and IgGb were evident. Specific nasal mucosal IgA persisted in most ponies until day 69. A second immunization on day 140 boosted antibody responses, and stimulated a strong nasal mucosal IgA response in the pony that failed to make an IgA response after primary immunization. At the termination of the experiment, IgA and IgGb dominated jejunal antibody responses whereas vaginal responses were mainly IgA. The latter response unequivocally confirms the existence of a common mucosal immune system in equids. The results indicate that a S. typhimurium Deltacya Deltacrp-pabA mutant has potential as an intranasal vaccine against salmonellosis in the horse.

Adenylyl Cyclases↗
PubMed2001

Intranasal immunogenicity of a Deltacya Deltacrp-pabA mutant of Salmonella enterica serotype Typhimurium for the horse.

The aim of this study was to investigate the intranasal immunogenicity for the horse of a Deltacya Deltacrp-pabA mutant (MGN-707) of Salmonella enterica serotype Typhimurium (S. typhimurium). MGN-707 caused no sign of disease, was not detected in feces and a single administration induced strong Salmonella-specific serum and nasal mucosal antibody responses. All ponies had made strong salmonella specific serum IgGa, IgGb, IgA and IgM antibody responses by day 25 after the first immunization. IgM responses to salmonella lipopolysaccharide (LPS) were short lived whereas salmonella specific serum IgGa and IgGb persisted at high levels in all ponies until 83 and 140 days, respectively. Specific nasal mucosal antibody responses dominated by IgA and IgM were evident by day 25 in all ponies except one in which only specific IgGa and IgGb were evident. Specific nasal mucosal IgA persisted in most ponies until day 69. A second immunization on day 140 boosted antibody responses, and stimulated a strong nasal mucosal IgA response in the pony that failed to make an IgA response after primary immunization. At the termination of the experiment, IgA and IgGb dominated jejunal antibody responses whereas vaginal responses were mainly IgA. The latter response unequivocally confirms the existence of a common mucosal immune system in equids. The results indicate that a S. typhimurium Deltacya Deltacrp-pabA mutant has potential as an intranasal vaccine against salmonellosis in the horse.

Adenylyl Cyclases↗
PubMed2001

Bacteremia associated with live attenuated chi8110 Salmonella enterica serovar Typhi ISP1820 in healthy adult volunteers.

Live attenuated chi8110 Salmonella enterica serovar Typhi ISP1820 vaccine was given in a dose-escalation trial to healthy, adult volunteers. Positive stool and blood cultures were noted, but limited, as were immune responses measured by ELISA and ELISPOT. Only volunteers with bacteremia developed immune responses; however, no symptoms were associated with bacteremia. The vaccine was insufficiently immunogenic for use as a vaccine. It is possible that reduced survival in the gut and reduced immunogenicity may have been due to the thawing of frozen inocula immediately prior to use.

Adolescent↗
PubMed2001

MlrA, a novel regulator of curli (AgF) and extracellular matrix synthesis by Escherichia coli and Salmonella enterica serovar Typhimurium.

Production of curli (AgF) adhesins by Escherichia coli and Salmonella enterica serovar Typhimurium (S. typhimurium) is associated with extracellular matrix production and is optimal at low temperature during stationary phase. Curli and extracellular matrix synthesis involves a complex regulatory network that is dependent on the CsgD (AgfD) regulator. We have identified a novel regulator, termed MlrA, that is required for curli production and extracellular matrix formation. Two cosmids from a genomic library of avian pathogenic E. coli chi7122 conferred mannose-resistant haemagglutination (HA) and curli production to E. coli HB101, which is unable to produce curli owing to a defective regulatory pathway. The rpoS gene, encoding a known positive regulator of curli synthesis, and the E. coli open reading frame (ORF) of unknown function, yehV, identified on each of these cosmids, respectively, conferred curli production and HA to E. coli HB101. We have designated yehV as the mlrA gene for MerR-like regulator A because its product shares similarities with regulatory proteins of the MerR family. HA and curli production by strain chi7122 were abolished by disruption of rpoS, mlrA or csgA, the curli subunit gene. Both csgD and csgBA transcription, required for expression of curli, were inactive in an mlrA mutant grown under conditions that promote curli production. An mlrA homologue was identified in S. typhimurium. Analysis of mlrA-lac operon fusions demonstrated that mlrA was positively regulated by rpoS. mlrA mutants of wild-type S. typhimurium SL1344 or SR-11 no longer produced curli or rugose colony morphology, and exhibited enhanced aggregation and extracellular matrix formation when complemented with the mlrA gene from either S. typhimurium or E. coli present on a low-copy-number plasmid. However, inactivation of mlrA did not affect curli production and aggregative morphology in an upregulated curli producing S. typhimurium derivative containing a temperature- and RpoS-independent agfD promoter region. These results indicate that MlrA is a newly defined transcriptional regulator of csgD/agfD that acts as a positive regulator of RpoS-dependent curli and extracellular matrix production by E. coli and S. typhimurium.

Adhesins, Bacterial↗
PubMed2001

Identification of Salmonella typhi genes expressed within macrophages by selective capture of transcribed sequences (SCOTS).

Salmonella enterica serovar Typhi (S. typhi) is a human-restricted pathogen which causes typhoid fever. Relatively little is known about S. typhi host interaction as animal models of this disease are severely limited by the lack of virulence of S. typhi in other hosts. The virulence of other Salmonella serovars in animal models is dependent on the abilities of these bacteria to survive within host macrophages. We have used selective capture of transcribed sequences (SCOTS) to identify S. typhi genes expressed during growth in human macrophages. This positive cDNA selection technique identified 28 distinct clones representing previously identified as well as novel, uncharacterized and hypothetical gene sequences that are expressed intracellularly. Transcripts for the Vi capsular antigen and genes whose products are involved in stress responses and nutrient acquisition were obtained from intracellular bacteria using SCOTS. Most of these clones are present in the S. typhimurium genome and are also expressed in murine macrophages. Nineteen of these gene sequences were disrupted insertionally in S. typhi, and most of the resulting mutants exhibited a lower level of survival within macrophages compared with the wild-type parent strain. Mutant strains, transformed with a copy of a wild-type gene, exhibited a macrophage survival level similar to that of the parental strain.

Bacterial Proteins↗
PubMed2000

Expression of the rfa, LPS biosynthesis promoter in Salmonella typhimurium during invasion of intestinal epithelial cells.

Salmonella regulates transcription of many of its genes in response to environmental conditions encountered inside or outside the eukaryotic cells it infects. In this paper, we examined Salmonella typhimurium gene expression within epithelial cells, by using bacterial luciferase as a reporter. We focused on gene expression controlled by Salmonella rfa promoter, using lac promoter as a control. We observed down regulation for both promoters during the initial 2 h of invasion. The decreased levels of luciferase activity appeared to be due to metabolic changes, since we observed similar results with tissue culture medium alone. Gene expression stabilized to a new steady state for the Salmonella rfa promoter, while a lac promoter activity steadily decreased. Bacterial luciferase activity was a good indicator of intracellular numbers and allowed us to detect as few as 1000 bacterial cells/infected monolayer. Both promoters were not dependent on host protein synthesis for expression.

Cell Line↗
PubMed2000

Secretion of virulence determinants by the general secretory pathway in gram-negative pathogens: an evolving story.

Secretion of proteins by the general secretory pathway (GSP) is a two-step process requiring the Sec translocase in the inner membrane and a separate substrate-specific secretion apparatus for translocation across the outer membrane. Gram-negative bacteria with pathogenic potential use the GSP to deliver virulence factors into the extracellular environment for interaction with the host. Well-studied examples of virulence determinants using the GSP for secretion include extracellular toxins, pili, curli, autotransporters, and crystaline S-layers. This article reviews our current understanding of the GSP and discusses examples of terminal branches of the GSP which are utilized by factors implicated in bacterial virulence.

Adenosine Triphosphatases↗
PubMed2000

Relationship between the Tsh autotransporter and pathogenicity of avian Escherichia coli and localization and analysis of the Tsh genetic region.

The temperature-sensitive hemagglutinin Tsh is a member of the autotransporter group of proteins and was first identified in avian-pathogenic Escherichia coli (APEC) strain chi7122. The prevalence of tsh was investigated in 300 E. coli isolates of avian origin and characterized for virulence in a 1-day-old chick lethality test. Results indicate that among the tsh-positive APEC isolates, 90.6% belonged to the highest virulence class. Experimental inoculation of chickens with chi7122 and an isogenic tsh mutant demonstrated that Tsh may contribute to the development of lesions within the air sacs of birds but is not required for subsequent generalized infection manifesting as perihepatitis, pericarditis, and septicemia. Conjugation and hybridization experiments revealed that the tsh gene is located on a ColV-type plasmid in many of the APEC strains studied, including strain chi7122, near the colicin V genes in most of these strains. DNA sequences flanking the tsh gene of strain chi7122 include complete and partial insertion sequences and phage-related DNA sequences, some of which were also found on virulence plasmids and pathogenicity islands present in various E. coli pathotypes and other pathogenic members of the Enterobacteriaceae. These results demonstrate that the tsh gene is frequently located on the ColV virulence plasmid in APEC and suggest a possible role of Tsh in the pathogenicity of E. coli for chickens in the early stages of infection.

Adhesins, Escherichia coli↗
PubMed1999

Molecular basis for the enterocyte tropism exhibited by Salmonella typhimurium type 1 fimbriae.

Salmonella typhimurium exhibits a distinct tropism for mouse enterocytes that is linked to their expression of type 1 fimbriae. The distinct binding traits of Salmonella type 1 fimbriae is also reflected in their binding to selected mannosylated proteins and in their ability to promote secondary bacterial aggregation on enterocyte surfaces. The determinant of binding in Salmonella type 1 fimbriae is a 35-kDa structurally distinct fimbrial subunit, FimHS, because inactivation of fimHS abolished binding activity in the resulting mutant without any apparent effect on fimbrial expression. Surprisingly, when expressed in the absence of other fimbrial components and as a translational fusion protein with MalE, FimHS failed to demonstrate any specific binding tropism and bound equally to all cells and mannosylated proteins tested. To determine if the binding specificity of Salmonella type 1 fimbriae was determined by the fimbrial shaft that is intimately associated with FimHS, we replaced the amino-terminal half of FimHS with the corresponding sequence from Escherichia coli FimH (FimHE) that contains the receptor binding domain of FimHE. The resulting hybrid fimbriae bearing FimHES on a Salmonella fimbrial shaft exhibited binding traits that resembled that of Salmonella rather than E. coli fimbriae. Apparently, the quaternary constraints imposed by the fimbrial shaft on the adhesin determine the distinct binding traits of S. typhimurium type 1 fimbriae.

Adhesins, Bacterial↗
PubMed1999

Protection and immune responses induced by attenuated Salmonella typhimurium UK-1 strains.

We previously reported that Salmonella typhimurium SR-11 mutants with deletion mutations in the genes encoding adenylate cyclase (cya) and the cAMP receptor protein (crp) are avirulent and protective in mice. Salmonella typhimurium UK-1 is highly virulent for chicks (oral LD50 of 3x10(3) CFU) and mice (oral LD50 of 8.5x10(3) CFU) and is capable of lethal infections in pigs, calves and horses. We postulated that attenuated derivatives of this lethal strain would probably induce a higher level of protective immunity than achieved with attenuated derivatives of less virulent S. typhimurium strains such as SR11. To test this hypothesis, we have constructed S. typhimurium UK-1 Deltacya-12Deltacrp-11 mutant strain chi3985 and its virulence plasmid cured derivative chi4095 to investigate their avirulence and immunogenicity in mice. We found that the mutants are avirulent and able to induce protective immune responses in BALB/c mice. These mutant strains retained wild-type ability to colonize the gut associated lymphoid tissue but reach and persist in spleen and liver at a significantly lower level than the wild-type parent strain. Mice survived oral infection with >1x10(9) CFU of chi3985 (the equivalent to 10(5) 50% lethal doses of wild-type S. typhimurium UK-1) and were fully protected against challenge with 10(5)times the LD50 of the wild-type parent. Immunized mice developed a high level of serum IgG titre to Salmonella LPS and delayed-type hypersensitivity (DTH) response to S. typhimurium outer membrane proteins. Compared to the virulence plasmid-containing strain chi3985, the virulence plasmid cured DeltacyaDeltacrp mutant strain chi4095 was more attenuated and less protective, as some mice immunized with chi4095 died when challenged with the wild-type UK-1 strain. This work demonstrates that S. typhimurium UK-1 Deltacrp Deltacya mutant strain may be a potential live vaccine to induce protective immunity against Salmonella infection or to deliver foreign antigens to the immune system.

Adenylyl Cyclases↗
PubMed1999

Effects of DksA and ClpP protease on sigma S production and virulence in Salmonella typhimurium.

Salmonella typhimurium responds to a variety of environmental stresses by accumulating the alternative sigma factor sigmaS. The repertoire of sigmaS -dependent genes that are subsequently expressed confers tolerance to a variety of potentially lethal conditions including low pH and stationary phase. The mechanism(s) responsible for triggering sigmaS accumulation are of considerable interest, because they help to ensure survival of the organism during encounters with suboptimal environments. Two genes associated with regulating sigmaS levels in S. typhimurium have been identified. The first is clpP, encoding the protease known to be responsible for degrading sigmaS in Escherichia coli. The second is dksA, encoding a protein of unknown function not previously associated with regulating sigmaS levels. As predicted, clpP mutants accumulated large amounts of sigmaS even in log phase. However, dksA mutants failed to accumulate sigmaS in stationary phase and exhibited lower accumulation during acid shock in log phase. DksA appears to be required for the optimal translation of rpoS based upon dksA mutant effects on rpoS transcriptional and translational lacZ fusions. The region of rpoS mRNA between codons 8 and 73 is required to see the effects of dksA mutations. This distinguishes the role of DksA from that of HF-I (hfq ) in rpoS translation, as the HF-I target area occurs well upstream of the rpoS start codon. DksA appears to be involved in the expression of several genes in addition to rpoS based on two-dimensional SDS-PAGE analysis of whole-cell proteins. As a result of their effects on gene expression, mutations in clpP and dksA decreased the virulence of S. typhimurium in mice, consistent with a role for sigmaS in pathogenesis.

Adenosine Triphosphatases↗
PubMed1999

Genomic subtractive hybridization and selective capture of transcribed sequences identify a novel Salmonella typhimurium fimbrial operon and putative transcriptional regulator that are absent from the Salmonella typhi genome.

Salmonella typhi, the etiologic agent of typhoid fever, is adapted to the human host and unable to infect nonprimate species. The genetic basis for host specificity in S. typhi is unknown. The avirulence of S. typhi in animal hosts may result from a lack of genes present in the broad-host-range pathogen Salmonella typhimurium. Genomic subtractive hybridization was successfully employed to isolate S. typhimurium genomic sequences which are absent from the S. typhi genome. These genomic subtracted sequences mapped to 17 regions distributed throughout the S. typhimurium chromosome. A positive cDNA selection method was then used to identify subtracted sequences which were transcribed by S. typhimurium following macrophage phagocytosis. A novel putative transcriptional regulator of the LysR family was identified as transcribed by intramacrophage S. typhimurium. This putative transcriptional regulator was absent from the genomes of the human-adapted serovars S. typhi and Salmonella paratyphi A. Mutations within this gene did not alter the level of S. typhimurium survival within macrophages or virulence within mice. A subtracted genomic fragment derived from the ferrichrome operon also hybridized to the intramacrophage cDNA. Nucleotide sequence analysis of S. typhimurium and S. typhi chromosomal sequences flanking the ferrichrome operon identified a novel S. typhimurium fimbrial operon with a high level of similarity to sequences encoding Proteus mirabilis mannose-resistant fimbriae. The novel fimbrial operon was absent from the S. typhi genome. The absence of specific genes may have allowed S. typhi to evolve as a highly invasive, systemic human pathogen.

Amino Acid Sequence↗
PubMed1999

Characterization of the avian pathogenic Escherichia coli hemagglutinin Tsh, a member of the immunoglobulin A protease-type family of autotransporters.

We reported earlier that a single gene, tsh, isolated from a strain of avian pathogenic Escherichia coli (APEC) was sufficient to confer on E. coli K-12 a hemagglutinin-positive phenotype and that the deduced sequence of the Tsh protein shared homology to the serine-type immunoglobulin A (IgA) proteases of Neisseria gonorrhoeae and Haemophilus influenzae. In this report we show that E. coli K-12 containing the recombinant tsh gene produced two proteins, a 106-kDa extracellular protein and a 33-kDa outer membrane protein, and was also able to agglutinate chicken erythrocytes. N-terminal sequence data indicated that the 106-kDa protein, designated Tshs, was derived from the N-terminal end of Tsh after the removal of a 52-amino-acid N-terminal signal peptide, while the 33-kDa protein, designated Tshbeta, was derived from the C-terminal end of Tsh starting at residue N1101. The Tshs domain contains the 7-amino-acid serine protease motif that includes the active-site serine (S259), found also in the secreted domains of the IgA proteases. However, site-directed mutagenesis of S259 did not abolish the hemagglutinin activity or the extracellular secretion of Tshs indicating that host-directed proteolysis was mediating the release of Tshs. Studies with an E. coli K-12 ompT mutant strain showed that the surface protease OmpT was not needed for the secretion of Tshs. Tsh belongs to a subclass of the IgA protease family, which also includes EspC of enteropathogenic E. coli, EspP of enterohemorragic E. coli, and SepA and VirG of Shigella flexneri, which seem to involve a host endopeptidase to achieve extracellular release of their N-terminal domains. In proteolytic studies conducted in vitro, Tshs did not cleave the substrate of the IgA proteases, human IgA1 or chicken IgA, and did not show proteolytic activity in a casein-based assay. Correlation of Tsh expression and hemagglutination activity appears to be a very complex phenomenon, influenced by strain and environmental conditions. Nevertheless, for both APEC and recombinant E. coli K-12 strains containing the tsh gene, it was only the whole bacterial cells and not the cell-free supernatants that could confer hemagglutinin activity. Our results provide insights into the expression, secretion, and proteolytic features of the Tsh protein, which belongs to the growing family of gram-negative bacterial extracellular virulence factors, named autotransporters, which utilize a self-mediated mechanism to achieve export across the bacterial cell envelope.

Adhesins, Escherichia coli↗
PubMed1999

The nature of the attenuation of Salmonella typhimurium strains expressing human papillomavirus type 16 virus-like particles determines the systemic and mucosal antibody responses in nasally immunized mice.

We have recently shown by using a recombinant Salmonella typhimurium PhoPc strain in mice the feasibility of using a Salmonella-based vaccine to prevent infection by the genital human papillomavirus type 16 (HPV16). Here, we compare the HPV16-specific antibody responses elicited by nasal immunization with recombinant S. typhimurium strains harboring attenuations that, in contrast to PhoPc, are suitable for human use. For this purpose, chi4989 (Deltacya Deltacrp) and chi4990 [Deltacya Delta(crp-cdt)] were constructed in the ATCC 14028 genetic background, and comparison was made with the isogenic PhoPc and PhoP- strains. Although the levels of expression of HPV16 virus-like particle (VLP) were similar in all strains, only PhoPc HPV16 induced sustained specific antibody responses after nasal immunization, while all strains induced high antibody responses with a single nasal immunization when an unrelated viral hepatitis B core antigen was expressed. The level of the specific antibody responses induced did not correlate with the number of recombinant bacteria surviving in various organs 2 weeks after immunization. Our data suggest that the immunogenicity of attenuated Salmonella vaccine strains does not correlate with either the number of persisting bacteria after immunization or the levels of in vitro expression of the antigen carried. Rather, the PhoPc phenotype appears to provide the unique ability in Salmonella to induce immune responses against HPV16 VLPs.

Animals↗
PubMed1999

Attenuation and immunogenicity of Deltacya Deltacrp derivatives of Salmonella choleraesuis in pigs.

Six different isogenic Deltacya Deltacrp derivatives of a strain of Salmonella choleraesuis var. kunzendorf-chi3246 virulent for pigs were constructed by transposon-mediated deletion mutagenesis. These strains were evaluated for virulence and ability to elicit a protective immune response in young weaned pigs after oral administration and were compared to a commercially available vaccine which lacks the 50-kb virulence plasmid (vpl(-)). These derivatives were Deltacya Deltacrp vpl(+), Deltacya Deltacrp vpl(-), Deltacya Delta(crp-cdt) vpl(+), Deltacya Delta(crp-cdt) vpl(-), Deltacya Deltacrp pmi-3834 vpl(+), and Deltacya Delta(crp-cdt) pmi-3834. In experiments to evaluate safety, no significant adverse effects of any of the vaccine constructs were observed, except that two of the strains which carried the virulence plasmid (vpl(+)) caused a small, short-term elevation in maximum temperature compared to pretreatment temperature values. Orally immunized animals, except for those vaccinated with the Deltacya Deltacrp pmi-3834 vpl(+) strain or SC-54, developed significant serum antibody responses 21 days postvaccination as measured by enzyme-linked immunosorbent assay. No cell-mediated immune responses to heat-killed S. choleraesuis were noted at the same time point as measured with heat-killed bacteria as antigen in a lymphocyte proliferation assay. In an oral challenge exposure model with a highly virulent heterologous strain of S. choleraesuis, the Deltacya Deltacrp strains with deletions in pmi were not protective. As measured by morbidity scores, the responses to challenge of the pigs vaccinated with the other four Deltacya Deltacrp derivatives were significantly better than those of the nonvaccinated, challenged group. With the exception of temperature elevation and slight differences in diarrhea scores postchallenge, none of these strains differed significantly from each other in the other clinical parameters analyzed. While the commercial vaccine was protective by most of the parameters measured, it was not fully protective against challenge with virulent S. choleraesuis as judged by diarrhea scores and temperature elevation. Collectively, these data demonstrate that Deltacya Deltacrp derivatives, with or without the virulence plasmid but not with deletions in the pmi gene, are candidates for vaccines for protection against salmonellosis in pigs.

Animals↗
PubMed1998

Virulence of a Salmonella typhimurium OmpD mutant.

An ompD mutation caused by a Tn10 insertion was transduced into Salmonella typhimurium SL1344 and UK-1. The adherence and invasion capabilities of the resultant ompD mutants were examined by tissue culture analysis. The virulence of the S. typhimurium ompD mutants was ascertained by a 50% lethal dose (LD50) study and by determining colonization ability with BALB/c mice. We found no statistically significant difference in adherence and invasion capacities between the S. typhimurium wild type strains and their corresponding ompD mutants. Furthermore, the LD50 and colonization studies revealed that there is no statistically significant difference in virulence between the S. typhimurium wild type strains and their corresponding ompD mutants. These results differ from those reported previously (C. J. Dorman, S. Chatfield, C. F. Higgins, C. Hayward, and G. Dougan, Infect. Immun. 57:2136-2140, 1989).

Animals↗
PubMed1998

Molecular and functional characterization of Salmonella enterica serovar typhimurium poxA gene: effect on attenuation of virulence and protection.

Salmonella enterica poxA mutants exhibit a pleiotropic phenotype, including reduced pyruvate oxidase activity; reduced growth rate; and hypersensitivity to the herbicide sulfometuron methyl, alpha-ketobutyrate, and amino acid analogs. These mutants also failed to grow in the presence of the host antimicrobial peptide, protamine. In this study, PoxA- mutants of S. enterica serovar Typhimurium (S. typhimurium) were found to be 10,000-fold attenuated in orally inoculated BALB/c mice and 1,000-fold attenuated in intraperitoneally inoculated BALB/c mice, compared to wild-type S. typhimurium UK-1. In addition, poxA mutants were found to be capable of colonizing the spleen, mesenteric lymph nodes, and Peyer's patches; to induce strong humoral immune responses; and to protect mice against a lethal wild-type Salmonella challenge. A 2-kb DNA fragment was isolated from wild-type S. typhimurium UK-1 based on its ability to complement an isogenic poxA mutant. The nucleotide sequence of this DNA fragment revealed an open reading frame of 325 amino acids capable of encoding a polypeptide of 36.8 kDa that was confirmed in the bacteriophage T7 expression system. Comparison of the translated sequence to the available databases indicated high homology to a family of lysyl-tRNA synthetases. Our results indicate that a mutation of poxA has an attenuating effect on Salmonella virulence. Further, poxA mutants are immunogenic and could be useful in designing live vaccines with a variety of bacterial species. To our knowledge, this is the first report on the effect of poxA mutation on bacterial virulence.

Animals↗