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  • 1
    In: Infection and Immunity, American Society for Microbiology, Vol. 81, No. 7 ( 2013-07), p. 2405-2414
    Abstract: Clostridium perfringens type D causes disease in sheep, goats, and other ruminants. Type D isolates produce, at minimum, alpha and epsilon (ETX) toxins, but some express up to five different toxins, raising questions about which toxins are necessary for the virulence of these bacteria. We evaluated the contribution of ETX to C. perfringens type D pathogenicity in an intraduodenal challenge model in sheep, goats, and mice using a virulent C. perfringens type D wild-type strain (WT), an isogenic ETX null mutant ( etx mutant), and a strain where the etx mutation has been reversed ( etx complemented). All sheep and goats, and most mice, challenged with the WT isolate developed acute clinical disease followed by death in most cases. Sheep developed various gross and/or histological changes that included edema of brain, lungs, and heart as well as hydropericardium. Goats developed various effects, including necrotizing colitis, pulmonary edema, and hydropericardium. No significant gross or histological abnormalities were observed in any mice infected with the WT strain. All sheep, goats, and mice challenged with the isogenic etx mutant remained clinically healthy for ≥24 h, and no gross or histological abnormalities were observed in those animals. Complementation of etx knockout restored virulence; most goats, sheep, and mice receiving this complemented mutant developed clinical and pathological changes similar to those observed in WT-infected animals. These results indicate that ETX is necessary for type D isolates to induce disease, supporting a key role for this toxin in type D disease pathogenesis.
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
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    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2013
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  • 2
    In: Infection and Immunity, American Society for Microbiology, Vol. 79, No. 11 ( 2011-11), p. 4569-4577
    Abstract: Internalization of Staphylococcus aureus in bovine endothelial cells (BEC) is increased by tumor necrosis factor alpha stimulation and NF-κB activation. Because the phosphoinositide-3-kinase (PI3K)–Akt signaling pathway also modulates NF-κB activity, we considered whether the internalization of S. aureus by BEC is associated with the activity of PI3K and Akt. We found a time- and multiplicity of infection-dependent phosphorylation of Akt on Ser473 in BEC infected with S. aureus . This phosphorylation was inhibited by LY294002 (LY), indicating the participation of PI3K. Inhibition of either PI3K with LY or wortmannin, or Akt with SH-5, strongly reduced the internalization of S. aureus . Transfection of BEC with a dominant-negative form of the Akt gene significantly decreased S. aureus internalization, whereas transfection with the constitutively active mutant increased the number of internalized bacterium. Inhibition of PDK1 activity with OSU-03012 did not affect the level of S. aureus internalization, demonstrating that phosphorylation of Akt on Thr308 is not important for this process. Compared to the untreated control, the adherence of S. aureus to the surface of BEC was unaltered when cells were transfected or incubated with the pharmacological inhibitors. Furthermore, Akt activation by internalized S. aureus triggered a time-dependent phosphorylation of glycogen synthase kinase-3α (GSK-3α) on Ser21 and GSK-3β on Ser9 that was partially inhibited with SH-5. Finally, treatment of BEC with LY prior to S. aureus infection inhibited the NF-κB p65 subunit phosphorylation on Ser536, indicating the involvement of PI3K. These results suggest that PI3K-Akt activity is important for the internalization of S. aureus and phosphorylation of GSK-3α, GSK-3β, and NF-κB.
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
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    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2011
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  • 3
    In: Infection and Immunity, American Society for Microbiology, Vol. 81, No. 9 ( 2013-09), p. 3163-3172
    Abstract: Na + /H + antiporters are ubiquitous membrane proteins that play a central role in the ion homeostasis of cells. In this study, we examined the possible role of Na + /H + antiport in Yersinia pestis virulence and found that Y. pestis strains lacking the major Na + /H + antiporters, NhaA and NhaB, are completely attenuated in an in vivo model of plague. The Y. pestis derivative strain lacking the nhaA and nhaB genes showed markedly decreased survival in blood and blood serum ex vivo . Complementation of either nhaA or nhaB in trans restored the survival of the Y. pestis nhaA nhaB double deletion mutant in blood. The nhaA nhaB double deletion mutant also showed inhibited growth in an artificial serum medium, Opti-MEM, and a rich LB-based medium with Na + levels and pH values similar to those for blood. Taken together, these data strongly suggest that intact Na + /H + antiport is indispensable for the survival of Y. pestis in the bloodstreams of infected animals and thus might be regarded as a promising noncanonical drug target for infections caused by Y. pestis and possibly for those caused by other blood-borne bacterial pathogens.
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
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    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2013
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  • 4
    Online Resource
    Online Resource
    American Society for Microbiology ; 2013
    In:  Infection and Immunity Vol. 81, No. 4 ( 2013-04), p. 1186-1197
    In: Infection and Immunity, American Society for Microbiology, Vol. 81, No. 4 ( 2013-04), p. 1186-1197
    Abstract: Yersinia pestis , the causative agent of plague, uses a type III secretion system (T3SS) to inject cytotoxic Yop proteins directly into the cytosol of mammalian host cells. The T3SS can also be activated in vitro at 37°C in the absence of calcium. The chromosomal gene rfaL ( waaL ) was recently identified as a virulence factor required for proper function of the T3SS. RfaL functions as a ligase that adds the terminal N -acetylglucosamine to the lipooligosaccharide core of Y. pestis . We previously showed that deletion of rfaL prevents secretion of Yops in vitro . Here we show that the divalent cations calcium, strontium, and magnesium can partially or fully rescue Yop secretion in vitro , indicating that the secretion phenotype of the rfaL mutant may be due to structural changes in the outer membrane and the corresponding feedback inhibition on the T3SS. In support of this, we found that the defect can be overcome by deleting the regulatory gene lcrQ . Consistent with a defective T3SS, the rfaL mutant is less virulent than the wild type. We show here that the virulence defect of the mutant correlates with a decrease in both T3SS gene expression and ability to inject innate immune cells, combined with an increased sensitivity to cationic antimicrobial peptides.
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
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    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2013
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  • 5
    In: Infection and Immunity, American Society for Microbiology, Vol. 80, No. 10 ( 2012-10), p. 3559-3569
    Abstract: A comprehensive Tn phoA mutant library was constructed in Yersinia pestis KIM6 to identify surface proteins involved in Y. pestis host cell invasion and bacterial virulence. Insertion site analysis of the library repeatedly identified a 9,042-bp chromosomal gene (YPO3944), intimin/invasin-like protein (Ilp), similar to the Gram-negative intimin/invasin family of surface proteins. Deletion mutants of ilp were generated in Y. pestis strains KIM5(pCD1 + ) Pgm − (pigmentation negative)/, KIM6(pCD1 − ) Pgm + , and CO92. Comparative analyses were done with the deletions and the parental wild type for bacterial adhesion to and internalization by HEp-2 cells in vitro , infectivity and maintenance in the flea vector, and lethality in murine models of systemic and pneumonic plague. Deletion of ilp had no effect on bacterial blockage of flea blood feeding or colonization. The Y. pestis KIM5 Δ ilp strain had reduced adhesion to and internalization by HEp-2 cells compared to the parental wild-type strain ( P 〈 0.05). Following intravenous challenge with Y. pestis KIM5 Δ ilp , mice had a delayed time to death and reduced dissemination to the lungs, livers, and kidneys as monitored by in vivo imaging using a lux reporter system ( in vivo imaging system [IVIS]) and bacterial counts. Intranasal challenge in mice with Y. pestis CO92 Δ ilp had a 55-fold increase in the 50% lethal dose ([LD 50 ] 1.64 × 10 4 CFU) compared to the parental wild-type strain LD 50 (2.98 × 10 2 CFU). These findings identified Ilp as a novel virulence factor of Y. pestis .
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
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    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2012
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  • 6
    Online Resource
    Online Resource
    American Society for Microbiology ; 2012
    In:  Infection and Immunity Vol. 80, No. 11 ( 2012-11), p. 3804-3811
    In: Infection and Immunity, American Society for Microbiology, Vol. 80, No. 11 ( 2012-11), p. 3804-3811
    Abstract: The strong epidemiological association between cigarette smoke (CS) exposure and respiratory tract infections is conventionally attributed to immunosuppressive and irritant effects of CS on human cells. Since pathogenic bacteria such as Staphylococcus aureus are members of the normal microbiota and reside in close proximity to human nasopharyngeal cells, we hypothesized that bioactive components of CS might affect these organisms and potentiate their virulence. Using Staphylococcus aureus as a model organism, we observed that the presence of CS increased both biofilm formation and host cell adherence. Analysis of putative molecular pathways revealed that CS exposure decreased expression of the quorum-sensing agr system, which is involved in biofilm dispersal, and increased transcription of biofilm inducers such as sarA and rbf . CS contains bioactive compounds, including free radicals and reactive oxygen species, and we observed transcriptional induction of bacterial oxidoreductases, including superoxide dismutase, following exposure. Moreover, pretreatment of CS with an antioxidant abrogated CS-mediated enhancement of biofilms. Exposure of bacteria to hydrogen peroxide alone increased biofilm formation. These observations are consistent with the hypothesis that CS induces staphylococcal biofilm formation in an oxidant-dependent manner. CS treatment induced transcription of fnbA (encoding fibronectin binding protein A), leading to increased binding of CS-treated staphylococci to immobilized fibronectin and increased adherence to human cells. These observations indicate that the bioactive effects of CS may extend to the resident microbiota of the nasopharynx, with implications for the pathogenesis of respiratory infection in CS-exposed humans.
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
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    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2012
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  • 7
    In: Infection and Immunity, American Society for Microbiology, Vol. 79, No. 4 ( 2011-04), p. 1512-1525
    Abstract: The Burkholderia pseudomallei K96243 genome encodes six type VI secretion systems (T6SSs), but little is known about the role of these systems in the biology of B. pseudomallei . In this study, we purified recombinant Hcp proteins from each T6SS and tested them as vaccine candidates in the BALB/c mouse model of melioidosis. Recombinant Hcp2 protected 80% of mice against a lethal challenge with K96243 , while recombinant Hcp1, Hcp3, and Hcp6 protected 50% of mice against challenge. Hcp6 was the only Hcp constitutively produced by B. pseudomallei in vitro ; however, it was not exported to the extracellular milieu. Hcp1, on the other hand, was produced and exported in vitro when the VirAG two-component regulatory system was overexpressed in trans . We also constructed six hcp deletion mutants ( Δhcp1 through Δhcp6 ) and tested them for virulence in the Syrian hamster model of infection. The 50% lethal doses (LD 50 s) for the Δhcp2 through Δhcp6 mutants were indistinguishable from K96243 ( 〈 10 bacteria), but the LD 50 for the Δhcp1 mutant was 〉 10 3 bacteria. The hcp1 deletion mutant also exhibited a growth defect in RAW 264.7 macrophages and was unable to form multinucleated giant cells in this cell line. Unlike K96243 , the Δhcp1 mutant was only weakly cytotoxic to RAW 264.7 macrophages 18 h after infection. The results suggest that the cluster 1 T6SS is essential for virulence and plays an important role in the intracellular lifestyle of B. pseudomallei .
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
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    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2011
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  • 8
    In: Infection and Immunity, American Society for Microbiology, Vol. 81, No. 9 ( 2013-09), p. 3089-3098
    Abstract: During urinary tract infections (UTIs), uropathogenic Escherichia coli must maintain a delicate balance between sessility and motility to achieve successful infection of both the bladder and kidneys. Previous studies showed that cyclic dimeric GMP (c-di-GMP) levels aid in the control of the transition between motile and nonmotile states in E. coli . The yfiRNB locus in E. coli CFT073 contains genes for YfiN, a diguanylate cyclase, and its activity regulators, YfiR and YfiB. Deletion of yfiR yielded a mutant that was attenuated in both the bladder and the kidneys when tested in competition with the wild-type strain in the murine model of UTI. A double yfiRN mutant was not attenuated in the mouse model, suggesting that unregulated YfiN activity and likely increased cytoplasmic c-di-GMP levels cause a survival defect. Curli fimbriae and cellulose production were increased in the yfiR mutant. Expression of yhjH , a gene encoding a proven phosphodiesterase, in CFT073 Δ yfiR suppressed the overproduction of curli fimbriae and cellulose and further verified that deletion of yfiR results in c-di-GMP accumulation. Additional deletion of csgD and bcsA , genes necessary for curli fimbriae and cellulose production, respectively, returned colonization levels of the yfiR deletion mutant to wild-type levels. Peroxide sensitivity assays and iron acquisition assays displayed no significant differences between the yfiR mutant and the wild-type strain. These results indicate that dysregulation of c-di-GMP production results in pleiotropic effects that disable E. coli in the urinary tract and implicate the c-di-GMP regulatory system as an important factor in the persistence of uropathogenic E. coli in vivo .
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
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    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2013
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  • 9
    In: Infection and Immunity, American Society for Microbiology, Vol. 80, No. 8 ( 2012-08), p. 2826-2834
    Abstract: Urinary tract infections (UTI), primarily caused by uropathogenic Escherichia coli (UPEC), are one of the leading bacterial infections due to their high frequency and rate of recurrence. Both type 1 pilus adhesive organelles ( fim ) and the QseC sensor kinase have been implicated in UPEC virulence during UTI and have been individually reported to be promising drug targets. Deletion of qseC leads to pleiotropic effects due to unregulated activation of the cognate response regulator QseB, influencing conserved metabolic processes and diminishing expression of virulence genes, including type 1 pili. Here, we discern the type 1 pilus-dependent and -independent effects that contribute to the virulence attenuation of a UPEC qseC deletion mutant in a murine model of experimental UTI. We show that although a Δ qseC mutant restored for type 1 pilus expression regains the ability to colonize the host and initiate acute infection up to 16 h postinfection, it is rapidly outcompeted during acute infection when coinoculated with a wild-type strain. As a result, this strain has a diminished capacity to establish chronic infection. A prophylactic oral dose of a FimH small-molecular-weight antagonist (ZFH-02056) further reduced the ability of the qseC mutant to establish chronic infection. Thus, loss of QseC significantly enhances the efficacy of ZFH-02056. Collectively, our work indicates that type 1 pili and QseC become critical in different infection stages, and that dual targeting of these factors has an additive effect on ablating UPEC virulence.
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
    RVK:
    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2012
    detail.hit.zdb_id: 1483247-1
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  • 10
    In: Infection and Immunity, American Society for Microbiology, Vol. 79, No. 5 ( 2011-05), p. 1863-1872
    Abstract: Citrobacter rodentium infection of mice induces cell-mediated immune responses associated with crypt hyperplasia and epithelial β-catenin signaling. Recent data suggest that phosphatidylinositol-3-kinase (PI3K)/Akt signaling cooperates with Wnt to activate β-catenin in intestinal stem and progenitor cells through phosphorylation at Ser552 (P-β-catenin 552 ). Our aim was to determine whether epithelial PI3K/Akt activation is required for β-catenin signaling and host defense against C. rodentium . C57BL/6 mice were infected with C. rodentium and treated with dimethyl sulfoxide (DMSO) (vehicle control) or with the PI3K inhibitor LY294002 or wortmannin. The effects of infection on PI3K activation and β-catenin signaling were analyzed by immunohistochemistry. The effects of PI3K inhibition on host defense were analyzed by the quantification of splenic and colon bacterial clearance, and adaptive immune responses were measured by real-time PCR (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). Increased numbers of P-β-catenin 552 -stained epithelial cells were found throughout expanded crypts in C. rodentium colitis. We show that the inhibition of PI3K signaling attenuates epithelial Akt activation, the Ser552 phosphorylation and activation of β-catenin, and epithelial cell proliferative responses during C. rodentium infection. PI3K inhibition impairs bacterial clearance despite having no impact on mucosal cytokine (gamma interferon [IFN-γ], tumor necrosis factor [TNF] , interleukin-17 [IL-17], and IL-1β) or chemokine (CXCL1, CXCL5, CXCL9, and CXCL10) induction. The results suggest that the host defense against C. rodentium requires epithelial PI3K activation to induce Akt-mediated β-catenin signaling and the clearance of C. rodentium independent of adaptive immune responses.
    Type of Medium: Online Resource
    ISSN: 0019-9567 , 1098-5522
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    Language: English
    Publisher: American Society for Microbiology
    Publication Date: 2011
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