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At least 379 records · Page 21Linked to original sources
PubMed1983

Detection of the extracellular proteases of Bacteroides nodosus in polyacrylamide gels: a rapid method of distinguishing virulent and benign ovine isolates.

The extracellular proteases of Bacteroides nodosus were separated electrophoretically on polyacrylamide slab gels at pH 8 . 8. Proteolytic activity was detected by placing the gel slab on a layer of gelatin-agar and allowing hydrolysis of the gelatin to occur. After two hours at 37 degrees C, the unhydrolysed gelatin was precipitated with mercuric chloride in acid. The proteolytic zymograms of 14 benign strains were identical. The zymograms of 10 virulent strains yielded two closely related sets of proteases. The reproducible difference observed between the respective zymograms readily provides a rapid diagnostic test to assist in the identification of benign and virulent strains of B nodosus.

Animals↗
PubMed1984

Pathogenic synergism.

Microbial synergy is well recognized but its role in the pathogenesis of human infections is poorly understood and probably underestimated. Recent experiments with animal models and in vitro studies should facilitate a more objective and critical assessment of the contribution to various infections by microorganisms, individually and collectively.

Actinomycosis↗
PubMed1980

Serotypic and biochemical characterization of Bacteroides nodosus isolates from Oregon.

Ninety-seven Bacteroides nodosus isolates were characterized by the tube agglutination test. Fourteen serotypes were identified including isolates that were serologically similar to Australian serotypes A, B and C. One additional isolate remains untyped and possibly represents another serotype. The isolates were cultured from 20 different flocks. Multiple isolates were obtained from 15 of the flocks and 13 of these had two to seven different B. nodosus serotypes. Eleven B. nodosus isolates representing one Australian and ten Oregon serotypes were nonfermentative in various carbohydrates and did not produce indole. These isolates all exhibited proteolytic activity. The prototype strains of 12 of the 14 serotypes demonstrated virulence as assessed by an elastase production assay.

Agglutination Tests↗
PubMed1994

Experimental evaluation of a commercial footrot vaccine against native Canadian strains of Dichelobacter nodosus.

Two serotypes of the anaerobic bacterium Dichelobacter nodosus were used to experimentally infect young sheep resulting in infectious pododermatitis or footrot characteristic of the natural disease in sheep. The specific serotypes of D. nodosus were reisolated from the feet and identified using immunofluorescent microscopy of hoof scrapings. Prior immunization of sheep with a commercially available bacterin containing whole cell preparations of ten strains of D. nodosus resulted in serum IgG reactive to a serotype of D. nodosus common to the vaccine. Immunization also produced serum IgG reactive to a serotype of D. nodosus not incorporated in the vaccine. A less severe infection occurred in the immunized sheep than in the controls regardless of the serotype of bacteria used to infect them. Clinical lameness and lesion severity were milder in sheep infected with the serotype of D. nodosus common to the vaccine. Western blot analysis of sera from convalescent sheep showed cross-reactive antibodies to nonfimbrial cell surface proteins, as well as bacterial lipopolysaccharide. Such cross-reactivity may explain the partial protection seen in animals infected with a serotype distinctive from the ones in the vaccine. Despite the historical emphasis of fimbrial immunogens in ovine footrot this study using a new model of experimental ovine footrot suggests other surface antigens may also be important in protective immunity.

Animals↗
PubMed1994

The laboratory culture of Dichelobacter nodosus in a footrot eradication program.

As part of a program to eradicate virulent footrot from Western Australia, 2745 isolates of Dichelobacter nodosus were isolated from 5263 specimens from 1883 submissions. The virulence of each isolate was assessed using protease thermostability and isoenzyme zymogram. We describe changes to the materials and methods required to handle these specimens and to reduce the interval between submission and report to 8 days.

Aerobiosis↗
PubMed1998

Serological classification and virulence determination of Dichelobacter nodosus isolated from Alberta and British Columbia sheep.

Ovine footrot is a contagious disease of sheep that occurs in temperature climates. It is caused by the strict anaerobe, Dichelobacter nodosus. Benign and virulent organisms are differentiated according to serotype and protease production. This study was conducted to identify the presence of virulent serotypes of D. nodosus in sheep flocks in Alberta and British Columbia. Dichelobacter nodosus was detected in lame sheep from 11 of 15 (73%) flocks in Alberta and in 4 of 5 (80%) British Columbia flocks. It was recovered from 57 of 107 (53%) lame sheep. In Alberta, 4 distinct serotypes were isolated from the 11 positive flocks while in British Columbia a total of 6 different serotypes were isolated. One British Columbia isolate could not be classified into existing serotypes. Of the 19 field strains tested, all but 3 were defined as virulent based upon the rapid rise in protease activity in vitro which was maintained between 3 and 5 d. The knowledge of the serotype and virulence of the D. nodosus isolated from affected animals can assist in the control and prevention of ovine footrot.

Alberta↗
PubMed2001

Introduction of the phzH gene of Pseudomonas chlororaphis PCL1391 extends the range of biocontrol ability of phenazine-1-carboxylic acid-producing Pseudomonas spp. strains.

Pseudomonas chlororaphis PCL1391 controls tomato foot and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici. Its biocontrol activity is mediated by the production of phenazine-1-carboxamide (PCN). In contrast, the take-all biocontrol strains P. fluorescens 2-79 and P. aureofaciens 30-84, which produce phenazine-1-carboxylic acid (PCA), do not control this disease. To determine the role of the amide group in biocontrol, the PCN biosynthetic genes of strain PCL1391 were identified and characterized. Downstream of phzA through phzG, the novel phenazine biosynthetic gene phzH was identified and shown to be required for the presence of the 1-carboxamide group of PCN because a phzH mutant of strain PCL1391 accumulated PCA. The deduced PhzH protein shows homology with asparagine synthetases that belong to the class II glutamine amidotransferases, indicating that the conversion of PCA to PCN occurs via a transamidase reaction catalyzed by PhzH. Mutation of phzH caused loss of biocontrol activity, showing that the 1-carboxamide group of PCN is crucial for control of tomato foot and root rot. PCN production and biocontrol activity of the mutant were restored by complementing the phzH gene in trans. Moreover, transfer of phzH under control of the tac promoter to the PCA-producing biocontrol strains P. fluorescens 2-79 and P. aureofaciens 30-84 enabled these strains to produce PCN instead of PCA and suppress tomato foot and root rot. Thus, we have shown, for what we believe is the first time, that the introduction of a single gene can efficiently extend the range of the biocontrol ability of bacterial strains.

Amino Acid Sequence↗
PubMed2006

Induction of plant defense enzymes and phenolics by treatment with plant growth-promoting rhizobacteria Serratia marcescens NBRI1213.

In greenhouse experiments, plant growth-promoting rhizobacteria (PGPR) Serratia marcescens NBRI1213 was evaluated for plant growth promotion and biologic control of foot and root rot of betelvine caused by Phytophthora nicotianae. Bacterization of betelvine (Piper betle L.) cuttings with S. marcescens NBRI1213 induced phenylalanine ammonia-lyase, peroxidase, and polyphenoloxidase activities in leaf and root. Qualitative and quantitative estimation of phenolic compounds was done through high-performance liquid chromatography (HPLC) in leaf and root of betelvine after treatment with S. marcescens NBRI1213 and infection by P. nicotianae. Major phenolics detected were gallic, protocatechuic, chlorogenic, caffeic, ferulic, and ellagic acids by comparison of their retention time with standards through HPLC. In all of the treated plants, synthesis of phenolic compounds was enhanced compared with control. Maximum accumulation of phenolics was increased in S. marcescens NBRI1213-treated plants infected with P. nicotianae. In a greenhouse test, bacterization using S. marcescens NBRI1213 decreased the number of diseased plants compared with nonbacterized controls. There were significant growth increases in shoot length, shoot dry weight, root length, and root dry weight, averaging 81%, 68%, 152%, and 290%, respectively, greater than untreated controls. This is the first report of PGPR-mediated induction of phenolics for biologic control and their probable role in protecting betelvine against P. nicotianae, an important soil-borne phytopathogenic fungus.

Hydroxybenzoates↗
PubMed2006

Effects of the tomato pathogen Fusarium oxysporum f. sp. radicis-lycopersici and of the biocontrol bacterium Pseudomonas fluorescens WCS365 on the composition of organic acids and sugars in tomato root exudate.

The effects of the pathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici and of the bacterial biocontrol strain Pseudomonas fluorescens WCS365, and of both microbes, on the amounts and composition of root exudate components of tomato plants grown in a gnotobiotic stonewool substrate system were studied. Conditions were selected under which introduction of F. oxysporum f. sp. radicis-lycopersici caused severe foot and root rot, whereas inoculation of the seed with P. fluorescens WCS365 decreased the percentage of diseased plants from 96 to 7%. This is a much better disease control level than was observed in potting soil. Analysis of root exudate revealed that the presence of F. oxysporum f. sp. radicis-lycopersici did not alter the total amount of organic acids, but that the amount of citric acid decreased and that of succinic acid increased compared with the nontreated control. In contrast, in the presence of the P. fluorescens biocontrol strain WCS365, the total amount of organic acid increased, mainly due to a strong increase of the amount of citric acid, whereas the amount of succinic acid decreased dramatically. Under biocontrol conditions, when both microbes are present, the content of succinic acid decreased and the level of citric acid was similar to that in the nontreated control. The amount of sugar was approximately half that of the control sample when either one of the microbes was present alone or when both were present. Analysis of the interactions between the two microbes grown together in sterile tomato root exudate showed that WCS365 inhibited multiplication of F. oxysporum f. sp. radicis-lycopersici, whereas the fungus did not affect the number of CFU of the bacterium.

Carbohydrate Metabolism↗
PubMed2000

The sss colonization gene of the tomato-Fusarium oxysporum f. sp. radicis-lycopersici biocontrol strain Pseudomonas fluorescens WCS365 can improve root colonization of other wild-type pseudomonas spp.bacteria.

We show that the disease tomato foot and root rot caused by the pathogenic fungus Fusarium oxysporum f. sp. radicis-lycopersici can be controlled by inoculation of seeds with cells of the efficient root colonizer Pseudomonas fluorescens WCS365, indicating that strain WCS365 is a biocontrol strain. The mechanism for disease suppression most likely is induced systemic resistance. P. fluorescens strain WCS365 and P. chlororaphis strain PCL1391, which acts through the production of the antibiotic phenazine-1-carboxamide, were differentially labeled using genes encoding autofluorescent proteins. Inoculation of seeds with a 1:1 mixture of these strains showed that, at the upper part of the root, the two cell types were present as microcolonies of either one or both cell types. Microcolonies at the lower root part were predominantly of one cell type. Mixed inoculation tended to improve biocontrol in comparison with single inoculations. In contrast to what was observed previously for strain PCL1391, mutations in various colonization genes, including sss, did not consistently decrease the biocontrol ability of strain WCS365. Multiple copies of the sss colonization gene in WCS365 improved neither colonization nor biocontrol by this strain. However, introduction of the sss-containing DNA fragment into the poor colonizer P. fluorescens WCS307 and into the good colonizer P. fluorescens F113 increased the competitive tomato root tip colonization ability of the latter strains 16- to 40-fold and 8- to 16-fold, respectively. These results show that improvement of the colonization ability of wild-type Pseudomonas strains by genetic engineering is a realistic goal.

Endoribonucleases↗
PubMed2001

Phenazine-1-carboxamide production in the biocontrol strain Pseudomonas chlororaphis PCL1391 is regulated by multiple factors secreted into the growth medium.

Pseudomonas chlororaphis PCL1391 controls tomato foot and root rot caused by Fusarium oxysporum f. sp. radicis-lycopersici. The production of phenazine-1-carboxamide (PCN) is crucial for this biocontrol activity. In vitro production of PCN is observed only at high-population densities, suggesting that production is under the regulation of quorum sensing. The main autoinducer molecule produced by PCL1391 was identified structurally as N-hexanoyl-L-homoserine lactone (C6-HSL). The two other autoinducers that were produced comigrate with N-butanoyl-L-homoserine lactone (C4-HSL) and N-octanoyl-L-homoserine lactone (C8-HSL). Two PCL1391 mutants lacking production of PCN were defective in the genes phzI and phzR, respectively, the nucleotide sequences of which were determined completely. Production of PCN by the phzI mutant could be complemented by the addition of exogenous synthetic C6-HSL, but not by C4-HSL, C8-HSL, or any other HSL tested. Expression analyses of Tn5luxAB reporter strains of phzI, phzR, and the phz biosynthetic operon clearly showed that phzI expression and PCN production is regulated by C6-HSL in a population density-dependent manner. The introduction of multiple copies of the regulatory genes phzI and phzR on various plasmids resulted in an increase of the production of HSLs, expression of the PCN biosynthetic operon, and consequently, PCN production, up to a sixfold increase in a copy-dependent manner. Surprisingly, our expression studies show that an additional, yet unidentified factor(s), which are neither PCN nor C4-HSL or C8-HSL, secreted into the growth medium of the overnight cultures, is involved in the positive regulation of phzI, and is able to induce PCN biosynthesis at low cell densities in a growing culture, resulting in an increase of PCN production.

Antifungal Agents↗