Search results for "Virulence"
showing 10 items of 457 documents
Isolation and characterization of anavirulent Candida albicansyeast monomorphic mutant
2003
Mutagenesis of Candida albicans strain ATCC 26555 with N-methyl-nitro-N-nitrosoguanidine followed by plating on solid yeast nitrogen base-N-acetylglucosamine medium at 37 degrees C yielded colony morphology variants that were characterized as forming smooth colonies, in contrast to the rough colonies formed by the parental strain. One yeast monomorphic mutant, CAL4, was studied in detail. Strain CAL4 is defective in filamentous growth, unable to form hyphae or pseudohyphae in vivo and in vitro. These filamentous structures are not elicited by commonly used external stimuli such as serum. The mutant had no obvious alterations in its mannan, glucan or chitin content. The total quantity of non…
Saprophytism of a fish pathogen as a transmission strategy
2009
Fish farming creates conditions where disease transmission is enhanced and antibiotic treatments are commonly used to cure bacterial diseases to prevent severe losses due to infections. Ability to persist in such an environment has been suggested to lead to the evolution of high virulence. Columnaris disease caused by Flavobacterium columnare is a growing problem in freshwater fish farming. Transmission of the disease is poorly known, and survival of F. columnare in the rearing environment has not been studied. This paper addresses both transmission of columnaris disease and survival strategy of F. columnare. Saprophytic activity of F. columnare was studied by infecting rainbow trout finger…
Phobalysin, a Small β-Pore-Forming Toxin of Photobacterium damselae subsp. damselae
2015
ABSTRACT Photobacterium damselae subsp. damselae , an important pathogen of marine animals, may also cause septicemia or hyperaggressive necrotizing fasciitis in humans. We previously showed that hemolysin genes are critical for virulence of this organism in mice and fish. In the present study, we characterized the hlyA gene product, a putative small β-pore-forming toxin, and termed it phobalysin P (PhlyP), for “photobacterial lysin encoded on a plasmid.” PhlyP formed stable oligomers and small membrane pores, causing efflux of K + , with no significant leakage of lactate dehydrogenase but entry of vital dyes. The latter feature distinguished PhlyP from the related Vibrio cholerae cytolysin…
Photobacterium damselae subsp. damselae Major Virulence Factors Dly, Plasmid-Encoded HlyA, and Chromosome-Encoded HlyA Are Secreted via the Type II S…
2015
ABSTRACT Photobacterium damselae subsp. damselae is a marine bacterium that causes septicemia in marine animals and in humans. Previously, we had determined a major role of pPHDD1 plasmid-encoded Dly (damselysin) and HlyA (HlyA pl ) and the chromosome-encoded HlyA (HlyA ch ) hemolysins in virulence. However, the mechanisms by which these toxins are secreted remain unknown. In this study, we found that a mini-Tn 10 transposon mutant in a plasmidless strain showing an impaired hemolytic phenotype contained an insertion in epsL , a component of a type II secretion system (T2SS). Reconstruction of the mutant by allelic exchange confirmed the specific involvement of epsL in HlyA ch secretion. In…
Assembly of human contact phase proteins and release of bradykinin at the surface of curli-expressing Escherichia coli.
1996
Previous work has demonstrated that most strains of the human pathogen Streptococcus pyogenes bind kininogens through M protein, a fibrous surface protein and virulence determinant. Here we find that strains of several other pathogenic bacterial species, both Gram-positive and Gram-negative, isolated from patients with sepsis, also bind kininogens, especially kininogen (HK). The most pronounced interaction was seen between HK and Escherichia coli. Among clinical isolates of E. coli, the majority of the enterohaemorrhagic, enterotoxigenic, and sepsis strains, but none of the enteroinvasive and enteropathogenic strains, bound HK. Binding of HK to E. coli correlated with the expression of curl…
The Influence of Infective Dose on the Virulence of a Generalist Pathogen in Rainbow Trout (Oncorhynchus mykiss) and Zebra Fish (Danio rerio)
2015
Pathogen density and genetic diversity fluctuate in the outside-host environment during and between epidemics, affecting disease emergence and the severity and probability of infections. Although the importance of these factors for pathogen virulence and infection probability has been acknowledged, their interactive effects are not well understood. We studied how an infective dose in an environmentally transmitted opportunistic fish pathogen, Flavobacterium columnare, affects its virulence both in rainbow trout, which are frequently infected at fish farms, and in zebra fish, a host that is not naturally infected by F. columnare. We used previously isolated strains of confirmed high and low …
Intensive fish farming and the evolution of pathogen virulence: the case of columnaris disease in Finland.
2009
Ecological changes affect pathogen epidemiology and evolution and may trigger the emergence of novel diseases. Aquaculture radically alters the ecology of fish and their pathogens. Here we show an increase in the occurrence of the bacterial fish disease Flavobacterium columnare in salmon fingerlings at a fish farm in northern Finland over 23 years. We hypothesize that this emergence was owing to evolutionary changes in bacterial virulence. We base this argument on several observations. First, the emergence was associated with increased severity of symptoms. Second, F. columnare strains vary in virulence, with more lethal strains inducing more severe symptoms prior to death. Third, more vir…
Life History Trade-Offs and Relaxed Selection Can Decrease Bacterial Virulence in Environmental Reservoirs
2012
Pathogen virulence is usually thought to evolve in reciprocal selection with the host. While this might be true for obligate pathogens, the life histories of opportunistic pathogens typically alternate between within-host and outside-host environments during the infection-transmission cycle. As a result, opportunistic pathogens are likely to experience conflicting selection pressures across different environments, and this could affect their virulence through life-history trait correlations. We studied these correlations experimentally by exposing an opportunistic bacterial pathogen Serratia marcescens to its natural protist predator Tetrahymena thermophila for 13 weeks, after which we meas…
In Candida parapsilosis the ATC1 Gene Encodes for an Acid Trehalase Involved in Trehalose Hydrolysis, Stress Resistance and Virulence
2014
An ORF named CPAR2-208980 on contig 005809 was identified by screening a Candida parapsilosis genome data base. Its 67% identity with the acid trehalase sequence from C. albicans (ATC1) led us to designate it CpATC1. Homozygous mutants that lack acid trehalase activity were constructed by gene disruption at the two CpATC1 chromosomal alleles. Phenotypic characterization showed that atc1Δ null cells were unable to grow on exogenous trehalose as carbon source, and also displayed higher resistance to environmental challenges, such as saline exposure (1.2 M NaCl), heat shock (42°C) and both mild and severe oxidative stress (5 and 50 mM H2O2). Significant amounts of intracellular trehalose were …
Homozygous deletion of ATC1 and NTC1 genes in Candida parapsilosis abolishes trehalase activity and affects cell growth, sugar metabolism, stress res…
2015
A double homozygous atc1Δ/atc1Δ/ntc1Δ/ntc1Δ mutant (atc1Δ/ntc1Δ KO) was constructed in the pathogen opportunistic yeast Candida parapsilosis by disruption of the two chromosomal alleles coding for NTC1 gene (encoding a neutral trehalase) in a Cpatc1Δ/atc1Δ background (atc1Δ KO strain, deficient in acid trehalase). The Cpatc1Δ/ntc1Δ KO mutant failed to counteract the inability of Cpatc1Δ cells to metabolize exogenous trehalose and showed a similar growth pattern on several monosaccharides and disaccharides. However, upon prolonged incubation in either rich medium (YPD) or nutrient-starved medium the viability of Cpatc1Δ cells exhibited a sensitive phenotype, which was augmented by further Cp…