Search results for "Virulence"
showing 10 items of 457 documents
Two Host Clades, Two Bacterial Arsenals: Evolution through Gene Losses in Facultative Endosymbionts.
2015
International audience; Bacterial endosymbiosis is an important evolutionary process in insects, which can harbor both obligate and facultative symbionts. The evolution of these symbionts is driven by evolutionary convergence, and they exhibit among the tiniest genomes in prokaryotes. The large host spectrum of facultative symbionts and the high diversity of strategies they use to infect new hosts probably impact the evolution of their genome and explain why they undergo less severe genomic erosion than obligate symbionts. Candidatus Hamiltonella defensa is suitable for the investigation of the genomic evolution of facultative symbionts because the bacteria are engaged in specific relations…
A three-way perspective of stoichiometric changes on host–parasite interactions
2015
Changes in environmental nutrients play a crucial role in driving disease dynamics, but global patterns in nutrient-driven changes in disease are difficult to predict. In this paper we use ecological stoichiometry as a framework to review host–parasite interactions under changing nutrient ratios, focusing on three pathways: (i) altered host resistance and parasite virulence through host stoichiometry (ii) changed encounter or contact rates at population level, and (iii) changed host community structure. We predict that the outcome of nutrient changes on host–parasite interactions depends on which pathways are modified, and suggest that the outcome of infection could depend on the overlap in…
Toxic and enzymatic activities of Vibrio vulnificus biotype 2 with respect to host specificity
1996
In this work, the enzymatic activities of selected strains of biotypes 1 and 2 of Vabrio vulnificus were analyzed by using conventional methods and the API ZYM system. The toxic activities of extracellular products (ECPs) were further evaluated by in vitro and in vivo experiments. The ECPs of both biotypes (i) showed high-level hydrolytic activities, (ii) displayed cytotoxicity for fish cell lines, and (iii) were lethal for eels. Exotoxins seem to be proteinaceous since heat treatment of ECP samples destroyed their toxicity. Only biotype 2 strains were virulent for cels, suggesting that host specificity must be related to differences in cell surface properties. Infectivity trials with other…
Frequent coinfection of cells explains functional in vivo complementation between cytomegalovirus variants in the multiply infected host.
2005
In contrast to many other virus infections, primary cytomegalovirus (CMV) infection does not fully protect against reinfection. Accordingly, clinical data have revealed a coexistence of multiple human CMV variants/ strains in individual patients. Notably, the phenomenon of multiple infection was found to correlate with increased virus load and severity of CMV disease. Although of obvious medical relevance, the mechanism underlying this correlation is unknown. A weak immune response in an individual could be responsible for a more severe disease and for multiple infections. Alternatively, synergistic contributions of variants that differ in their biological properties can lead to qualitative…
Suppression of CD8+ T cell recognition in the immediate-early phase of human cytomegalovirus infection.
2012
Human cytomegalovirus (HCMV) interferes with MHC class I-restricted antigen presentation and thereby reduces recognition by CD8+ T-cells. This interference is mediated primarily by endoplasmic reticulum-resident glycoproteins that are encoded in the US2–11 region of the viral genome. Such a suppression of recognition would be of particular importance immediately after infection, because several immunodominant viral antigens are already present in the cell in this phase. However, which of the evasion proteins gpUS2–11 interfere(s) with antigen presentation to CD8+ T-cells at this time of infection is not known. Here we address this question, using recombinant viruses (RV) that express only o…
UME6, a Novel Filament-specific Regulator ofCandida albicansHyphal Extension and Virulence
2008
The specific ability of the major human fungal pathogen Candida albicans, as well as many other pathogenic fungi, to extend initial short filaments (germ tubes) into elongated hyphal filaments is important for a variety of virulence-related processes. However, the molecular mechanisms that control hyphal extension have remained poorly understood for many years. We report the identification of a novel C. albicans transcriptional regulator, UME6, which is induced in response to multiple host environmental cues and is specifically important for hyphal extension. Although capable of forming germ tubes, the ume6Δ/ume6Δ mutant exhibits a clear defect in hyphal extension both in vitro and during i…
Candida albicans adhesin Als3p is dispensable for virulence in the mouse model of disseminated candidiasis
2011
The presence of specific proteins, including Ece1p, Hwp1p and Als3p, distinguishes theCandida albicanshyphal cell wall from that of yeast-form cells. These proteins are thought to be important for the ability ofC. albicanscells to adhere to living and non-living surfaces and for the cell-to-cell adhesion necessary for biofilm formation, and also to be pivotal in mediatingC. albicansinteractions with endothelial cells. Using anin vitroflow adhesion assay, we previously observed that yeast cells bind in greater numbers to human microvascular endothelial cells than do hyphal or pseudohyphal cells. This is consistent with previous observations that, in a murine model of disseminated candidiasis…
Pseudohyphal Regulation by the Transcription Factor Rfg1p in Candida albicans
2010
ABSTRACT The opportunistic human fungal pathogen Candida albicans is a major cause of nosocomial infections. One of the fundamental features of C. albicans pathogenesis is the yeast-to-hypha transition. Hypha formation is controlled positively by transcription factors such as Efg1p and Cph1p, which are required for hyphal growth, and negatively by Tup1p, Rfg1p, and Nrg1p. Previous work by our group has shown that modulating NRG1 gene expression, hence altering morphology, is intimately linked to the capacity of C. albicans to cause disease. To further dissect these virulence mechanisms, we employed the same strategy to analyze the role of Rfg1p in filamentation and virulence. Studies using …
Physiologic Expression of the Candida albicans Pescadillo Homolog Is Required for Virulence in a Murine Model of Hematogenously Disseminated Candidia…
2012
ABSTRACT Morphogenetic conversions contribute to the pathogenesis of Candida albicans invasive infections. Many studies to date have convincingly demonstrated a link between filamentation and virulence; however, relatively little is known regarding the role of the filament-to-yeast transition during the pathogenesis of invasive candidiasis. We previously identified the C. albicans pescadillo homolog ( PES1 ) as essential during yeast growth and growth of lateral yeast on hyphae but not during hyphal growth. Furthermore, we demonstrated that PES1 is required for virulence in vivo in a Galleria mellonella larva model of candidiasis. Here, we have used a regulatable tetO-PES1 / pes1 strain to …
<i>Aeromonas hydrophila</i> subsp. <i>dhakensis</i> Isolated from Feces, Water and Fish in Mediterranean Spain
2012
Eight Aeromonas hydrophila-like arabinose-negative isolates from diverse sources (i.e., river freshwater, cooling-system water pond, diseased wild European eels, and human stools) sampled in Valencia (Spain) during 2004–2005, were characterized by 16S rRNA gene sequencing and extensive biochemical testing along with reference strains of most Aeromonas species. These isolates and all reference strains of A. hydrophila subsp. dhakensis and A. aquariorum showed a 16S rRNA sequence similarity of 99.8–100%, and they all shared an identical phenotype. This matched exactly with that of A. hydrophila subsp. dhakensis since all strains displayed positive responses to the Voges-Prokauer test and to t…