Pathogenic effects of Opolysaccharide from Shigella flexneri strain

RNA-seq analysis of the influence of anaerobiosis and FNR on Shigella flexneri

Background

Shigella flexneri is an important human pathogen that has to adapt to the anaerobic environment in the gastrointestinal tract to cause dysentery. To define the influence of anaerobiosis on the virulence of Shigella, we performed deep RNA sequencing to identify transcriptomic differences that are induced by anaerobiosis and modulated by the anaerobic Fumarate and Nitrate Reduction regulator, FNR.

Results

We found that 528 chromosomal genes were differentially expressed in response to anaerobic conditions; of these, 228 genes were also influenced by FNR. Genes that were up-regulated in anaerobic conditions are involved in carbon transport and metabolism (e.g. ptsG, manX, murQ, cysP, cra), DNA topology and regulation (e.g. ygiP, stpA, hns), host interactions (e.g. yciD, nmpC, slyB, gapA, shf, msbB) and survival within the gastrointestinal tract (e.g. shiA, ospI, adiY, cysP). Interestingly, there was a marked effect of available oxygen on genes involved in Type III secretion system (T3SS), which is required for host cell invasion and pathogenesis. These genes, located on the large Shigella virulence plasmid, were down regulated in anaerobiosis in an FNR-dependent manner. We also confirmed anaerobic induction of csrB and csrC small RNAs in an FNR-independent manner.

Conclusions

Anaerobiosis promotes survival and adaption strategies of Shigella, while modulating virulence plasmid genes involved in T3SS-mediated host cell invasion. The influence of FNR on this process is more extensive than previously appreciated, although aside from the virulence plasmid, this transcriptional regulator does not govern expression of genes on other horizontally acquired sequences on the chromosome such as pathogenicity islands.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-438) contains supplementary material, which is available to authorized users.

Topological investigation of glucosyltransferase V in Shigella flexneri using the substituted cysteine accessibility method

Modification of the lipopolysaccharide O-antigen of Shigella converts the serotype, which is significant as acquired immune responses are serotype specific. Glucosyltransferases (Gtrs) modify the O-antigen by the addition of glucosyl-groups; however the precise mechanism of O-antigen modification is not fully understood. This study aims to substantiate inferences made on the GtrV topological structure using the substituted cysteine accessibility method (SCAM). Twenty-one amino acid residues were tested to clarify three features of GtrV: the extramembrane regions, a proposed reentrant loop, and a membrane border region. Overall, the results agreed with a previous topology proposed for GtrV. The topology of GtrV consists of 11 extramembrane regions with a cytoplasmic N-terminus, periplasmic C-terminus and 9 transmembrane (TM) helices. The existence of a reentrant loop between TM helices IV and V was verified, and the cytoplasmic membrane border region of TM helix II was examined in depth.

Molecular pathogenesis of Shigella spp.: controlling host cell signaling, invasion, and death by type III secretion

Shigella spp. are gram-negative pathogenic bacteria that evolved from harmless enterobacterial relatives and may cause devastating diarrhea upon ingestion. Research performed over the last 25 years revealed that a type III secretion system (T3SS) encoded on a large plasmid is a key virulence factor of Shigella flexneri. The T3SS determines the interactions of S. flexneri with intestinal cells by consecutively translocating two sets of effector proteins into the target cells. Thus, S. flexneri controls invasion into EC, intra- and intercellular spread, macrophage cell death, as well as host inflammatory responses. Some of the translocated effector proteins show novel biochemical activities by which they intercept host cell signal transduction pathways. An understanding of the molecular mechanisms underlying Shigella pathogenesis will foster the development of a safe and efficient vaccine, which, in parallel with improved hygiene, should curb infections by this widespread pathogen.

O-antigen modal chain length in Shigella flexneri 2a is growth-regulated through RfaH-mediated transcriptional control of the wzy gene

Shigella flexneri 2a 2457T produces lipopolysaccharide (LPS) with two O-antigen (OAg) chain lengths: a short (S-OAg) controlled by WzzB and a very long (VL-OAg) determined by Wzz(pHS-2). This study demonstrates that the synthesis and length distribution of the S. flexneri OAg are under growth-phase-dependent regulation. Quantitative electrophoretic analysis showed that the VL-OAg increased during growth while the S-OAg distribution remained constant. Increased production of VL-OAg correlated with the growth-phase-regulated expression of the transcription elongation factor RfaH, and was severely impaired in a DeltarfaH mutant, which synthesized only low-molecular-mass OAg molecules and a small amount of S-OAg. Real-time RT-PCR revealed a drastic reduction of wzy polymerase gene expression in the DeltarfaH mutant. Complementation of this mutant with the wzy gene cloned into a high-copy-number plasmid restored the bimodal OAg distribution, suggesting that cellular levels of Wzy influence not only OAg polymerization but also chain-length distribution. Accordingly, overexpression of wzy in the wild-type strain resulted in production of a large amount of high-molecular-mass OAg molecules. An increased dosage of either wzzB or wzz(pHS-2) also altered OAg chain-length distribution. Transcription of wzzB and wzz(pHS-2) genes was regulated during bacterial growth but in an RfaH-independent manner. Overall, these findings indicate that expression of the wzy, wzzB and wzz(pHS-2) genes is finely regulated to determine an appropriate balance between the proteins responsible for polymerization and chain-length distribution of S. flexneri OAg.

Complete genome sequence of Shigella flexneri 5b and comparison with Shigella flexneri 2a

Background

Shigella bacteria cause dysentery, which remains a significant threat to public health. Shigella flexneri is the most common species in both developing and developed countries. Five Shigella genomes have been sequenced, revealing dynamic and diverse features. To investigate the intra-species diversity of S. flexneri genomes further, we have sequenced the complete genome of S. flexneri 5b strain 8401 (abbreviated Sf8401) and compared it with S. flexneri 2a (Sf301).

Results

The Sf8401 chromosome is 4.5-Mb in size, a little smaller than that of Sf301, mainly because the former lacks the SHI-1 pathogenicity island (PAI). Compared with Sf301, there are 6 inversions and one translocation in Sf8401, which are probably mediated by insertion sequences (IS). There are clear differences in the known PAIs between these two genomes. The bacteriophage SfV segment remaining in SHI-O of Sf8401 is clearly larger than the remnants of bacteriophage SfII in Sf301. SHI-1 is absent from Sf8401 but a specific related protein is found next to the pheV locus. SHI-2 is involved in one intra-replichore inversion near the origin of replication, which may change the expression of iut/iuc genes. Moreover, genes related to the glycine-betaine biosynthesis pathway are present only in Sf8401 among the known Shigella genomes.

Conclusion

Our data show that the two S. flexneri genomes are very similar, which suggests a high level of structural and functional conservation between the two serotypes. The differences reflect different selection pressures during evolution. The ancestor of S. flexneri probably acquired SHI-1 and SHI-2 before SHI-O was integrated and the serotypes diverged. SHI-1 was subsequently deleted from the S. flexneri 5b genome by recombination, but stabilized in the S. flexneri 2a genome. These events may have contributed to the differences in pathogenicity and epidemicity between the two serotypes of S. flexneri.

Identification of alkA gene related to virulence of Shigella flexneri 2a by mutational analysis

AIM: In vivo induced genes are thought to play an important role during infection of host. AlkA was identified as an in vivo-induced gene by in vivo expression technology (IVET), but its virulence in Shigella flexneri was not reported. The purpose of this study was to identify the role of alkA gene in the pathogenesis of S. flexneri.

METHODS: PCR was used to amplify alkA gene of S. flexneri 2a and fragment 028pKm. The fragment was then transformed into 2457T05 strain, a S flexneri 2a strain containing Red recombination system, which was constructed with a recombinant suicide plasmid pXLkd46. By in vivo homologous recombination, alkA mutants were obtained and verified by PCR and sequencing. Intracellular survival assay and virulence assay were used to test the intracellular survival ability in HeLa cell model and the virulence in mice lung infection model respectively.

RESULTS: Deletion mutant of S. flexneri 2a alkA was successfully constructed by λ Red recombination system. The mutant exhibited significant survival defects and much significant virulence defects in mice infection assay.

CONCLUSION: AlkA gene plays an important role in the infection of epithelial cells and is a virulent gene of Shigella spp.

Identification of RanBMP interacting with Shigella flexneri IpaC invasin by two-hybrid system of yeast

AIM: Bacillary dysentery caused by Shigella flexneri is still a threat to human health. Of four invasion plasmid antigen proteins (IpaA, B, C and D), IpaC plays an important role in the pathogenicity of this pathogen. The purpose of this study was to investigate the proteins interacting with IpaC in the host cell during the pathogenic process of this disease.

METHODS: By applying two-hybrid system, the bait plasmid containing ipaC gene was constructed and designated pGBKT-ipaC. The bait plasmid was transformed AH109, and proved to express IpaC and then HeLa cDNA library plasmids were introduced into the above transformed AH109. The transformation mixture was plated on medium lacking Trp, Leu, and His in the initial screen, then restreaked on medium lacking Trp, Leu, His and Ade. Colonies growing on the selection medium were further assayed for β-galactosidase activity. BLAST was carried out in the database after sequencing the inserted cDNA of the positive library plasmid.

RESULTS: Among the 2 × 10⁶ transformants, 64 positive clones were obtained as determined by activation of His, Ade and LacZ reporter genes. Sequence analysis revealed that cDNA inserts of two colonies were highly homologous to a known human protein, RanBPM.

CONCLUSION: These results provide evidence that IpaC may be involved in the invasion process of S. flexneri by interacting with RanBPM, and RanBPM is most likely to be the downstream target of IpaC in the cascade events of S. flexneri infection.

Distribution of nitric oxide synthase in stomach myenteric plexus of rats

AIM: To study the distribution of nitric oxide synthase (NOS) in rat stomach myenteric plexus.

METHODS: The distribution of NOS in gastric wall was studied in quantity and location by the NADPH-diaphorase (NDP) histochemical staining method and whole mount preparation technique.

RESULTS: NOS was distributed in whole stomach wall, most of them were located in myenteric plexus, and distributed in submucosal plexus. The shape of NOS positive neurons was basically similar, most of them being round and oval in shape. But their density, size and staining intensity varied greatly in the different parts of stomach. The density was 62 ± 38 cells/mm² (antrum), 43 ± 32 cells/mm² (body), and 32 ± 28 cells/mm² (fundus), respectively. The size and staining intensity of NOS positive neurons in the fundus were basically the same, the neurons being large and dark stained, while they were obviously different in antrum. In the body of the stomach, the NOS positive neurons were in an intermediate state from fundus to antrum. There were some beadlike structures which were strung together by NOS positive varicosities in nerve fibers, some were closely adherent to the outer walls of blood vessels.

CONCLUSION: Nitric oxide might be involved in the modulation of motility, secretion and blood circulation of the stomach, and the significant difference of NOS positive neurons in different parts of stomach myenteric plexus may be related to the physiologic function of stomach.

Animal experiment and clinical study of effect of gamma-interferon on hepatic fibrosis

AIM

To evaluate the antifibrotic effect of different doses of recombinant human Gamma-Interferon (IFN-gamma) in two rat models of hepatic fibrosis, and to observe its effect on moderate chronic hepatitis B virus fibrosis.

METHODS

Hepatic fibrosis was successfully induced in 150 and 196 rats by subcutaneous injection of carbon tetrachloride (CCl4) and intraperitoneal injection of dimethylnitrosamine (DMN), respectively. Each of the two model groups was divided into: (1) fibrotic model group; (2) colchicine treatment group (0.1 mg/kg/day, gastrogavage for 8 weeks); (3) high-dose IFN-gamma group (15 MU/kg per day, i.m. for 8 weeks); (4) medium-dose IFN-gamma group (5 MU/kg daily, i.m. for 8 weeks); and (5) Y low-dose IFN-gamma group (1.67 MU/kg daily, i.m. for 8 weeks). Another group of 10 rats without any treatment was used as normal controls. At the end of the experiment, semi-quantitative histopathological scores of inflammation and fibrosis, liver alpha smooth muscle actin (alpha-SMA) expression level, liver hydroxyl proline content and serum hyaluronic acid levels were compared. And 47 medium chronic hepatitis B viral fibrosis patients were studied. They were given IFN-gamma treatment, 100 MU/day i.m. for the first three months and 100 MU qod i.m. for the next six months. Semi-quantitative pathological scores of inflammation and fibrosis and serum hepatic fibrosis indices were compared within the 9 months.

RESULTS

In animal experiment, the pathological fibrosis scores and liver hydroxyl proline content were found to be significantly lower in rats treated with different doses of IFN-gamma as compared with rats in fibrotic model group induced by either CCl4 or DMN, in a dose-dependent manner. For CCl4-induced model, pathological fibrosis scores in high, medium and low doses IFN-gamma groups were 5.10 +/- 2.88, 7.70 +/- 3.53 and 8.00 +/- 3.30, respectively, but the score was 14.60 +/- 7.82 in fibrotic model group. Hydroxyl proline contents were 2.83 +/- 1.18, 3.59 +/- 1.22 and 4.80 +/- 1.62, in the three IFN-gamma groups, and 10.01 +/- 3.23 in fibrotic model group. The difference was statistically significant (P<0.01). Similar results were found in DMN-induced model. Pathological fibrosis scores were 6.30 +/- 0.48, 8.10 +/- 2.72 and 8.30 +/- 2.58, in high, medium and low doses IFN-gamma groups, and 12.60 +/- 3.57 in fibrotic model group. Hydroxyl proline contents were 2.72 +/- 0.58, 3.14 +/- 0.71 and 3.62 +/- 1.02, in the three IFN-gamma groups, and 12.79 +/- 1.54 in fibrotic model group. The difference was statistically significant (P<0.01). Serum hepatic fibrosis indices decreased significantly in the 47 patients after IFN-gamma treatment (HA: 433.38 +/- 373.00 vs 281.57 +/- 220.48; LN: 161.22 +/- 41.02 vs 146 +/- 35 +/- 44. 67; PC III: 192.59 +/- 89.95 vs 156.98 +/- 49.22; C-I: 156.30 +/- 44.01 vs 139.14 +/- 34.47) and the differences between the four indices were significant (P <0.05). Thirty-three patients received two liver biopsies, one before and one after IFN-gamma treatment. In thirty of 33 patients IFN-gamma had better effects according to semi-quantitative pathological scores (8.40 +/- 5.83 vs 5.30 +/- 4.05, P<0.05).

CONCLUSION

All the three doses of IFN-gamma are effective in treating rat liver fibrosis induced by either CCl4 or DMN, the higher the dose, the better the effect. And IFN-gamma is effective for patients with moderate chronic hepatitis B viral fibrosis.