摘要:

To determine the seroprevalence of Norwalk virus and whether Norwalk virus contributed to an observed increase in illness in tap water drinkers participating in a prospective epidemiological study, sera collected during the study were examined for changes in Norwalk virus antibody titer, using a specific enzyme immunoassay. Antibodies to Norwalk virus were measured in sera collected in March, June, and September 1988 and in June 1989, and antibodies were found in 79% of the individuals. Seroprevalence increased with age, being 55% (ages 9–19), 79% (20–39), 87% (40–49), 84% (50–59), and 100% (60 and older). Norwalk infections occurred in 33% of the individuals during the course of the study. The highest rate of infection (expressed as a monthly rate) was observed during the summer of 1988. These results confirm that a large number of infections owing to Norwalk viruses occur throughout the year. A previous seroconversion or a high serum titer were not always protective. Finally, there was no detectable difference in infection rate between consumers of tap water and consumers of water treated by reverse-osmosis units, suggesting that Norwalk virus infections were not responsible for the excess of gastrointestinal illness observed in tap water drinkers during this epidemiological study.Key words: drinking water, Norwalk virus, gastroenteritis, seroprevalence.

ISSN:0008-4166    

DOI:10.1139/m94-128

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

All tested isolates ofPhytophthora insolitaand an unknown asexualPhytophthoraspecies found in soil, ditch water, and diseased plant tissues in Taiwan produced ovoid, nonpapillate, nondeciduous sporangia on sporangiophores proliferating through an empty sporangium or in a nesting fashion, and formed irregular as well as spherical hyphal swellings. All testedPhytophthoraisolates grew at an unusually high temperature of 39 °C, displayed similar or identical electrophoretic patterns of soluble proteins, and produced α1hormone. The ability of one isolate ofP.insolitato produce oospores was decreased and that of another was lost completely during storage. The results suggest that all isolates of the asexualPhytophthorasp. tested werePhytophthora insolitaand were unable to produce oospores owing to a defect in the physiological process of sexual reproduction.Key words: asexualPhytophthora,Phytophthora insolita, high-temperaturePhytophthora, sexual reproduction.

ISSN:0008-4166    

DOI:10.1139/m94-129

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The oxidation of thiosulfate byThiobacillus thiooxidansgrown on sulfur was studied in cells, cell-free extracts, and a thiosulfate-oxidizing enzyme system. Thiosulfate was oxidized to tetrathionate by cells treated withN-ethylmaleimide with a pH optimum at 2.3. The cell-free extracts also oxidized thiosulfate with the same pH optimum and O2consumption. Untreated cells, on the other hand, oxidized thiosulfate to sulfite in the presence of 2-n-heptyl-4-hydroxyquinolineN-oxide, an inhibitor of sulfite oxidation. The cells treated withN-ethylmaleimide showed twoKmvalues for thiosulfate while the cell-free system showed only oneKm. TheKmvalue for thiosulfate generally increased with the increasing pH. A soluble thiosulfate-oxidizing enzyme system was extracted from the cells at pH 2.5 in the presence of 1 M ammonium sulfate by passage through a French pressure cell. The system contained a native cytochromecthat was reduced by thiosulfate at pH 2.5 and a thiosulfate-ferricyanide oxidoreductase activity with a pH optimum around 2.0. The acidic extract also contained a component that reduced horse heart cytochromecat a neutral pH. The reduction at an acidic pH required sulfite.Key words: thiosulfate oxidation,Thiobacillus thiooxidans, tetrathionate, sulfite.

ISSN:0008-4166    

DOI:10.1139/m94-130

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The isolation and characterization of four mutants ofRhizobium melilotiunable to synthesize poly-β-hydroxybutyrate (PHB) are reported. The mutants were independently obtained via Tn5transposon mutagenesis and exhibited physiological and cytomorphological characteristics similar to those of the parental strain, as well as overlapping DNA profiles. These were assessed at both the plasmid and total genome level, using for the latter the sensitive technique of pulsed-field gel electrophoresis in a contour-clamped homogeneous electric field. With respect to the parental PHB+strain, the loss of PHB-synthesizing ability in the four mutants was demonstrated by gas chromatography, transmission electron microscopy, and enzymatic tests. Localization studies of Tn5insertion showed that the PHB−phenotype had, in all mutants, a transposon insertion in the same region, although not in the same position. The symbiotic traits (nodule-inducing ability onMedicago sativaand acetylene-reducing activity of nodules) of the mutants did not differ significantly from those of the parentalR.meliloti.Key words:Rhizobium meliloti, poly-β-hydroxybutyrate (PHB), PHB synthase.

ISSN:0008-4166    

DOI:10.1139/m94-131

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The optimal incubation conditions for the direct viable count method with nalidixic acid were determined. They do not differ from those proposed in the literature for a laboratory strain and a mixed bacterial population isolated from drinking water. The direct viable count method with 5-cyano-2,3-ditolyl tetrazolium chloride (CTC) was performed under in situ conditions. The bacteria were incubated with CTC at a concentration of 1 mM for 4–6 h at the temperature of the water in the pipes and without the addition of an exogenous substrate. The results obtained for a laboratory strain using the two direct count methods were similar. However, for a mixed bacterial population, the counts were always higher with the CTC method than with the nalidixic acid method.Key words: drinking water, CTC, nalidixic acid, direct viable count.

ISSN:0008-4166    

DOI:10.1139/m94-132

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The total lipids ofMethanosarcina mazeiaccounted for 4.0% of the cell dry mass, and 90% of these were polar lipids. Nearly all of the polar fraction consisted of diether (2,3-di-O-phytanyl-sn-glycerol) and 3-hydroxydiether analogs of phosphatidylglycerol, phosphatidylinositol, phosphatidylserine, and phosphatidylethanolamine. Several highly fluorescent trace components in the lipid extracts were purified and partially characterized by mass spectrometry. Fast atom bombardment mass spectrometry of total lipid extracts provided data to establish a close relationship among the polar lipids present inMethanosarcina mazei,Methanosarcina thermophila,Methanosarcina acetivorans,Methanosarcina barkeriFusaro, andMethanosarcina barkeriMS.Key words: diether lipids, hydroxydiether lipids, fast atom bombardment mass spectrometry,Methanosarcina, archaeobacteria.

ISSN:0008-4166    

DOI:10.1139/m94-133

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

A chemotaxonomic study was carried out on representative strains of 13Aeromonasgenomic species. Quinone, polyamine, and fatty acid patterns were found to be very useful for an improved characterization of the genus and an improved differentiation from members of the familiesEnterobacteriaceaeandVibrionaceae. The Q-8-benzoquinone was the predominant ubiquinone, and putrescine and diaminopropane were the major poly amines of the genus. The fatty acid patterns of 181 strains, all characterized by DNA–DNA hybridization, showed a great homogeneity within the genus, with major amounts of hexadecanoic acid (16:0), hexadecenoic acid (16:1), and octadecenoic acid (18:1), and minor amounts of the hydroxylated fatty acids (3-OH 13:0, 2-OH 14:0, 3-OH 14:0) in addition to some iso and anteiso branched fatty acids (i-13:0, i-17:1, i-17:0, and a-17:0). Although some differences in fatty acid profiles between the genomic species could be observed, a clearcut differentiation of all species was not possible.Key words:Aeromonas, polyamines, quinones, fatty acids, differentiation.

ISSN:0008-4166    

DOI:10.1139/m94-134

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The effect of cultural (temperature and pH) and nutritional conditions (nitrogen and carbon source) on the flocculation expression of three strains was studied. The strains' flocculation ability was determined by placing the cells in a stationary phase of growth in standard flocculation conditions. The flocculation ability of strain NCYC 1195, recently classified in the literature as the NewFlo phenotype, was more sensitive to growth temperature than Flo1 phenotype strains (NCYC 869 and NRRL Y265). The initial pH of the culture medium did not affect the flocculation ability of Flo1 phenotype strains but in the case of strain NCYC 1195 flocculation was repressed when the initial pH of the culture medium was below 3.5. Flocculation in strain NCYC 1195 was also repressed in defined culture medium; this inhibition was not related to a deficiency in any particular nitrogen source, but rather to the poor buffering capacity of the defined medium. All strains showed strong flocculation when grown in glucose, but were nonflocculent in glycerol. It was clearly demonstrated that the phenotypic expression of flocculation could be induced or repressed by changing cultural and nutritional conditions. Two distinct behaviours were also displayed with regard to the effect of the cultural conditions upon flocculation, namely the effect of pH. These different behaviours can be used to distinguish the two flocculation phenotypes.Key words:Saccharomyces cerevisiae, flocculation, growth temperature, pH, nitrogen source.

ISSN:0008-4166    

DOI:10.1139/m94-135

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The fate of precursors of the isoprenoid pathway was studied in the sterol auxotrophLagenidium giganteumand in the positive control organismLagenidium callinectes. Acetate derived from glucose and mevalonic acid was converted to sterols and fatty acids inL.callinectes.Lagenidium giganteumconverted mevalonic acid to sterols and fatty acids, but glucose-derived acetate was not utilized for sterol synthesis. The results showed that the defect in the isoprenoid pathway ofL.giganteumoccurs at the level of the β-hydroxy-β-methylglutarylcoenzyme A reductase–synthase complex. Various aspects of this defect are discussed relative to metabolism of the organism.Key words:Lagenidium giganteum,Lagenidium callinectes, glucose, mevalonic acid utilization, fatty acids, sterol production.

ISSN:0008-4166    

DOI:10.1139/m94-136

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

In the absence of serum,Legionella pneumophilademonstrated wash-resistant adherence to U-937 cells, primary guinea-pig alveolar macrophages, and MRC-5 cells. Neither complement nor antibody was required for binding. The dynamics of adherence following inoculation ofL.pneumophilaat increasing 10-fold multiplicities of infection to each of the three host cell types resulted in a first-order kinetic relationship of binding, indicative of one bacterial adhesin molecule recognized by one host cell receptor moiety. Host cell receptor saturation studies showed that depending on the cell type, 2–8% of the bacterial inoculum adhered to cells under these nonopsonic conditions. Preliminary adhesin and receptor characterization studies were preformed to define the chemical composition of the binding structures on both the organism and the three different host cell surfaces. The adherence phenomenon was investigated using competitive binding assays in the presence of putative adhesin analogs as well as following treatments modifying the microbial and host cell surface membranes. Attachment was evaluated both by viable bacterial cell colony counts and by indirect immunofluorescent assay. With the exception of aldehyde treatments, the various membrane-modifying regimes and the presence of the adhesin analogs were shown to have no effect on organism or host cell viability. Data suggested that theL.pneumophilaadhesin responsible for opsonin-independent binding to these host cells was a protein structure with lectin-like properties. Furthermore, this protein would appear to be intimately associated with carbohydrate or lipid structures located on the bacterial outer membrane. The receptor moiety present on all host cells responsible for bindingL.pneumophilahad properties consistent with a carbohydrate or complex saccharide structure. To evaluate the role of complement receptors as the structures necessary forL.pneumophilainfection of macrophages, a battery of monoclonal antibodies were used to block the complement receptor (CR) types 1 (CD35), CR3 (CD 18, CD11b), and CR4 (CD18, CD11c). Blocking studies with CR-specific monoclonal antibodies indicated that CR1 and the integrin receptors CR3 and CR4 were not involved in the opsonin-independent binding ofL.pneumophilato macrophage-like cells.Key words:Legionella, opsonin-independent attachment, bacterial adherence, complement receptors, adhesion–receptor interactions.

ISSN:0008-4166    

DOI:10.1139/m94-137

出版商:NRC Research Press    

年代:1994

数据来源: NRC