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Highly Virulent (highly + virulent)
Selected AbstractsAcute columnaris infection in channel catfish, Ictalurus punctatus (Rafinesque): efficacy of practical treatments for warmwater aquaculture pondsJOURNAL OF FISH DISEASES, Issue 1 2004S Thomas-Jinu Abstract Columnaris disease was induced in channel catfish, Ictalurus punctatus (Rafinesque), by bath exposure to four highly virulent isolates of Flavobacterium columnare. In untreated controls, mortality began 20 h after exposure and reached 100% by 48 h. Mortality in channel catfish given antibiotic treatments with oxytetracycline or a combination of sulphadimethoxine and ormetoprim in feed prior to bacterial challenge was zero with all four strains of F. columnare. Diquat® (Zeneca Agricultural Products, Wilmington, DE, USA) was the most effective bath treatment; mortality with all four strains was zero. With potassium permanganate, chloramine-T, hydrogen peroxide and copper sulphate, bath treatment efficacy varied significantly among strains (P = 0.0346) and among treatments (P = 0.0033). Bath treatments with chloramine-T and potassium permanganate significantly reduced (P < 0.05) mortality from 100 to 75 and 69%, respectively, but copper sulphate and hydrogen peroxide treatments were not effective. Based on our results, oral antibiotics prevented columnaris disease but, of the bath treatments, only Diquat® produced a dramatic reduction in the mortality of acutely infected fish. Diquat® is labelled for aquatic use as an herbicide in the USA but in large ponds it is prohibitively expensive. [source] The Rcs phosphorelay system is essential for pathogenicity in Erwinia amylovoraMOLECULAR PLANT PATHOLOGY, Issue 2 2009DONGPING WANG SUMMARY The Rcs phosphorelay system is a modified two-component signal transduction system found exclusively in Enterobacteriaceae. In this study, we characterized the roles of the Rcs system in Erwinia amylovora, a highly virulent and necrogenic enterobacterium causing fire blight disease on rosaceous plants. Our results showed that rcsB, rcsC, rcsD and rcsBD mutants were non-pathogenic on immature pear fruit. The bacterial growth of these mutants was also greatly reduced compared with that of the wild-type strain in immature pear fruit. In an in vitro amylovoran assay, rcsB and rcsD mutants were deficient in amylovoran production, whereas the rcsC mutant exhibited higher amylovoran production than that of the wild-type. Consistent with amylovoran production, expression of the amylovoran biosynthetic gene amsG, using green fluorescent protein as a reporter, was not detectable in rcsB, rcsD and rcsBD mutants both in vitro and in vivo. The expression of amsG in vitro was higher in the rcsC mutant than in the wild-type, whereas its expression in vivo was higher in the wild-type than in the rcsC mutant. In addition, rcs mutants were more susceptible to polymyxin B treatment than the wild-type, suggesting that the Rcs system conferred some level of resistance to polymyxin B. Furthermore, rcs mutants showed irregular and slightly reduced motility on swarming plates. Together, these results indicate that the Rcs system plays a major role in virulence and survival of E. amylovora in immature pear fruit. [source] Potential for recombinant Babesia bovis antigens to protect against a highly virulent isolatePARASITE IMMUNOLOGY, Issue 12 2005M. HOPE SUMMARY Two antigens from Babesia bovis,12D3 and 11C5, were expressed and purified as recombinant proteins in Escherichia coli and used to vaccinate groups of six Babesia -susceptible cattle. These were subsequently challenged with a highly virulent strain of B. bovis. All cattle showed symptoms of disease and most required treatment. Cattle vaccination groups receiving either 12D3 or 11C5 or a combination of both, reduced parasitaemia by approximately fourfold and a number of individual animals appeared to control the parasite infection. Control of parasites correlated with high monocyte numbers late in infection. The results thus confirm the potential usefulness of both antigens but also demonstrate the limitations of current formulations. [source] Novel in vivo use of a polyvalent Streptomyces phage to disinfest Streptomyces scabies -infected seed potatoesPLANT PATHOLOGY, Issue 6 2001F. McKenna A highly virulent and polyvalent Streptomyces phage was isolated from a potato field near Albany, Western Australia. The efficacy of the isolated phage to disinfest seed potato tubers artificially inoculated with a common scab-causing streptomycete was evaluated. The phage suspension was prepared in a mini-bioreactor. Diseased potatoes were bathed in a phage suspension (1 × 109 plaque-forming units per mL) for 24 h. The suspension was constantly circulated within a novel 25 L phage bath by means of an air-sparging pipe driven from an air compressor. Phage-treated scab-affected seed potatoes planted into free-draining polystyrene boxes containing steam-pasteurized field soil produced tuber progeny with significantly (P < 0·05) reduced levels of surface lesions of scab (1·2%) compared with tubers harvested from nonphage-treated tubers (23%). The number of scab lesions was also significantly reduced (P < 0·05) by phage treatment of mother tubers. No significant differences were recorded in weight, size or number of harvested tubers from phage-treated or nontreated mother tubers. This is the first in vivo study that has used Streptomyces phage to significantly disinfest seed potatoes of Streptomyces scabies and thereby reduce contamination of soil from seed-tuber-borne inoculum and reduce infection of daughter tubers. [source] Over-expression of TGA5, which encodes a bZIP transcription factor that interacts with NIM1/NPR1, confers SAR-independent resistance in Arabidopsis thaliana to Peronospora parasiticaTHE PLANT JOURNAL, Issue 2 2002Han Suk Kim Summary The Arabidopsis thaliana NIM1/NPR1 gene product is required for induction of systemic acquired resistance (SAR) by pathogens, salicylic acid (SA) or synthetic SA analogs. We identified, in a yeast two-hybrid screen, two NIM1/NPR1 interacting proteins, TGA2 and TGA5, which belong to the basic region, leucine zipper (bZIP) family of transcription factors. Both TGA2 and TGA5 strongly interact with NIM1/NPR1 in yeast and in vitro, and recognize the as-1 cis element found within the promoter of several pathogenesis-related genes, such as PR-1. To determine the role TGA2 and TGA5 may play in NIM1/NPR1-mediated disease resistance, we introduced sense and antisense versions of both genes into transgenic Arabidopsis plants. Characterization of TGA2 transgenic plants revealed that inhibition or overexpression of TGA2 does not significantly affect PR-1 expression or induction of SAR after pathogen infection or INA treatment. Surprisingly, all TGA5 -antisense transgenic plants produced showed increased accumulation of TGA5 transcripts compared with untransformed control plants, while the TGA5 -sense lines showed no significant increase in TGA5 mRNA levels. Interestingly, the high level of TGA5 mRNA in the antisense lines was accompanied by significant resistance to a highly virulent isolate of the oomycete pathogen Peronospora parasitica. Further, resistance was not coupled to accumulation of products from the SAR-linked PR-1 gene following inoculation with P. parasitica or treatment with INA, indicating that these plants express a robust, PR-1 -independent resistance mechanism. Resistance was retained when a TGA5 -accumulating line was combined genetically with a nim1-1 mutation or nahG (salicylate hydroxylase) transgene, indicating that resistance in these plants is due to an SA and SAR-independent mechanism. [source] | ||||||||||