摘要:

The present study was performed to assess the potential of a humoral mucosal immune response directed against the O157 antigen ofEscherichia coliO157:H7 to prevent intestinal colonization by the pathogen. To this end, mice were gavaged with inocula ofSalmonella landau, aSalmonellastrain that naturally expresses the O157 antigen.Salmonella landauwas avirulent for mice. Despite this, mice exposed toS. landaudeveloped high titres of serum and coproantibodies against the O157 antigen. These mice, compared with controls, demonstrated some ability to resist transient intestinal colonization by an oral inoculum of an isolate ofE. coliO157:H7. These findings suggest that a local immune response directed against the O157 antigen might increase host resistance to this pathogen.Key words:Salmonella landau, Escherichia coliO157:H7, mucosal immunity, mice.

ISSN:0008-4166    

DOI:10.1139/w99-059

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In Japan, antimicrobial agent therapy for patients with diarrhea due to enterovirulent organisms including enterohemorrhagicEscherichia coli(EHEC) is common, and norfloxacin (NFLX), fosfomycin, and kanamycin are recommended for EHEC treatment by the Japanese Ministry of Health and Welfare. The aim of this study was to analyze the effects of antimicrobial agents which have been used or recommended for the treatment of EHEC on the production of verotoxin (VT) in vitro. Subinhibitory concentrations of quinolones, NFLX, sparofloxacin (SPFX), and grepafloxacin (GPFX) markedly stimulated the productions of VT1 and VT2. The macrolide azithromycin (AZM), erythromycin (EM), and clarithromycin (CAM) did not stimulate the production of VT at a wide range of concentrations. These in vitro results indicate that when quinolones are prescribed for a patient infected with EHEC, the concentration of antimicrobial agents used in vivo and the susceptibility of the EHEC strains against quinolones should be taken into consideration.Key words: EHEC, O157:H7, verotoxin, quinolone, macrolide.

ISSN:0008-4166    

DOI:10.1139/w99-069

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The survival ofCryptosporidium parvumin source separated urine was investigated as part of a broader study on microbial risks associated with the reuse of human urine for sustainable agriculture. A dye permeability assay and in vitro excystation were the primary methods used to assess viability. In the collected urine most of the nitrogen is present as ammonia and the pH is generally around 9. Parallel investigations were made in buffers to compare possible toxic effects of urine to actual pH effects. Oocysts in the untreated urine were inactivated below the detection limit (1/300) within 63 days. This inactivation rate was significantly higher (P< 0.01) than in urine adjusted to pH 5 or 7 according to the dye permeability assay. The corresponding difference between different pH values was not seen in buffers, suggesting that the antiprotozoan effect of urine was mediated by other factors besides pH. The Swedish practice of storing urine for six months before its use thus appears satisfactory for the inactivation ofCryptosporidiumoocysts.Key words:Cryptosporidium parvum, oocysts, human urine, survival, source separation.

ISSN:0008-4166    

DOI:10.1139/w99-066

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Seasonal and spatial fluctuations in abundance, biomass production, and potential heterotrophic activity (i.e.,14C-glucose uptake) of bacterioplankton assemblages in a 1-year-old reservoir (the Sep Reservoir, Puy-de-Dôme, France) were examined concurrently with water temperature, phytoplankton chlorophyllaconcentration, and primary production (PP). Based on the values observed for these biological variables, the Sep Reservoir was considered to have evolved to an oligo-mesotrophic state. Spatiotemporal variations of bacterial variables were a consequence of the seasonal evolution of the reservoir coupled with the resource availability. Multivariate regression analyses suggest that about 14 and 26% of the variance in bacterial standing stock and activity may be explained by the physical environment (i.e., temperature) and a resource availability index (chlorophyllaconcentration or primary production), respectively. A carbon budget indicated that 4-126% (mean = 20%) of the ambient PP may be channeled through the microbial loop via bacterial biomass production. Heterotrophic bacterial production in the Sep Reservoir may therefore, on occasion, represent a significant source of carbon for higher order consumers.Key words: reservoirs, plankton, bacteria, heterotrophic uptake, primary and bacterial production

ISSN:0008-4166    

DOI:10.1139/w99-058

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Xanthomonas axonopodispv.manihotis(Xam) causes bacterial blight, a major disease of cassava, which is a starchy root crop that feeds about 500 million people throughout the world. To better select resistant cassava germplasm, we examined the population structure ofXamin Brazil, Latin America's largest producer of cassava, and a major center of diversity for the crop. The 79 strains collected between 1941 and 1996 from three edaphoclimatic zones were analyzed by restriction fragment length polymorphism (RFLP), using a probe linked to aXampathogenicity gene (pthB). Thirty-eight haplotypes were identified, and geographical differentiation for theXamstrains was demonstrated. Strains from subtropical zone (ECZ 6) showed high genetic diversity in most of the sites from which they were collected. They also showed migration from site to site. RFLP and amplified fragment length polymorphism (AFLP) analyses were carried out on 37Xamstrains and compared; the AFLP assays were performed using eight primer combinations. A multiple correspondence analysis, used to assess genetic relatedness among strains and estimate genetic diversity, indicated that the BrazilianXampopulation showed high diversity. No correlation was found between AFLP and RFLP data, but the two techniques provided complementary information on the genetic diversity ofXam. Most strains were highly aggressive on a susceptible cultivar. The genetic analysis presented here contributes to a better understanding of theXampopulation structure in Brazil and will help select strains of the pathogen for screening cassava germplasm resistant to the disease.Key words: cassava bacterial blight, resistance, genetic diversity, molecular characterization.

ISSN:0008-4166    

DOI:10.1139/w99-062

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Thaxtomin A production byStreptomyces scabiesis induced by plant extracts in culture media. We compared the production of thaxtomin A by threeStreptomyces scabiesstrains (EF-35, CG1, and ATCC 49173) in different culture media in a first attempt to identify the plant molecules required for the biosynthesis of thaxtomin A. Thaxtomin A production varied greatly among media and amongS. scabiesstrains. Strain CG1 presented a higher production than the other strains in all complex media. Oat bran broth is the best thaxtomin A production medium, and suberin is the only plant polymer allowing the production of thaxtomin A in minimal medium. The threeS. scabiesstrains had extracellular esterase activities when grown in the presence of potato suberin or oat bran. We suggest that extracellular esterases allow the release from lipid polymers of plant molecules that may act as inducers for thaxtomin A biosynthesis genes or as precursors in the biosynthetic pathway of thaxtomin A.Key words: common scab, phytotoxin, suberin, esterase.

ISSN:0008-4166    

DOI:10.1139/w99-072

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The internal transcribed spacer (ITS) of rDNA was analysed by PCR/RFLP in 66 strains belonging to 11 putative species of theMorchellaceaeand 3 species of theDiscinaceae. For certain taxa, in particularMorchella esculenta,Morchella conica, andMorchella elata, isolates from distant geographical origins were available. Nevertheless, no intraspecific variations of ITS length and restriction was noted. All genera were separated and withinMorchella; four putative species could be clearly distinguished in the group of the yellow morels (sectioadnatae). In contrast, no distinction could be obtained between the compared taxa in the group of the black morels (sectiodistantes). Sequence analyses of the ITS were performed in one strain of seven putativeMorchella. The sequence comparison confirmed the distinctions within the yellow morels and allowed us to separate one putative taxon from the others in black morels. Only the 5,8 gene could be aligned in all sequenced samples. The ITS1 and ITS2 sectors could only be aligned within the black and yellow morels, respectively. The genetic and phylogenetic distances between black and yellow morels, respectively revealed by maximum parsimony and neighbour joining analyses, both confirm the great distance between these species groups and address the question of a separation in the genusMorchella.Key words:Morchellaceae,Discinaceae, ITS.

ISSN:0008-4166    

DOI:10.1139/w99-070

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Nineteen monoclonal antibodies (Mabs) were isolated based on reactivity with disruptedPectinatus cerevisiiphiluscells. All of the Mabs reacted with cells from which the outer membrane had been stripped by incubation with sodium dodecyl sulphate, suggesting the peptidoglycan (PG) layer was involved in binding. Mab reactivity with purified PG confirmed this. Epitope mapping revealed the Mabs in total recognize four binding sites on the PG. Mabs specific for each of the four sites also bound strongly to disruptedPectinatus frisingensis,Selenomonas lacticifix,Zymophilus paucivorans, andZymophilus raffinosivoranscells, but weakly to disruptedMegasphaera cerevisiaecells. No antibody reactivity was seen with disrupted cells of 11 other species of Gram-negative bacteria. These results confirm that a common PG structure is used by several species of anaerobic Gram-negative beer spoilage bacteria. These results also indicate that PG-specific Mabs can be used to rapidly detect a range of anaerobic Gram-negative beer spoilage bacteria, provided the bacterial outer membrane is first removed to allow antibody binding.Key words: beer spoilage, epitope mapping, monoclonal antibodies,Pectinatus, peptidoglycan.

ISSN:0008-4166    

DOI:10.1139/w99-071

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Non-swarming mutants ofFlexibacter maritimusappeared at high frequency on &bgr;-lactam antibiotic-containing medium. Among them were several phenotypes characterized by changes in cell surface properties and cell envelope proteins, in adhesion and in resistance to &bgr;-lactams, including increased sensitivity to these antibiotics.Key words:Flexibacter, gliding, adhesion, &bgr;-lactam, antibiotic resistance.

ISSN:0008-4166    

DOI:10.1139/w99-067

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Using tRNAscan-SE and FAStRNA we have identified four tRNA genes in the delayed early region of the bacteriophage D3 genome (GenBank accession No. AF077308). These are specific for methionine (AUG), glycine (GGA), asparagine (AAC), and threonine (ACA). The D3 Thr- and Gly-tRNAs recognize codons, which are rarely used inPseudomonas aeruginosaand presumably, influence the rate of translation of phage proteins. BLASTN searches revealed that the D3 tRNA genes have homology to tRNA genes from Gram-positive bacteria. Analysis of codon usage in the 91 ORFs discovered in D3 indicates patterns of codon usage reminiscent ofEscherichia coliorP. aeruginosa.Key words: bacteriophage,Pseudomonas, D3, tRNA, codon usage.

ISSN:0008-4166    

DOI:10.1139/w99-078

出版商:NRC Research Press    

年代:1999

数据来源: NRC