摘要:

Staphylococcus lugdunensisandStaphylococcus schleiferi, two newly described species, have been isolated from numerous types of human infections. We compared the pathogenicity of 30 strains ofS.lugdunensis,S.schleiferi,Staphylococcus epidermidis,Staphylococcus warneri, andStaphylococcus hominis, using a mouse model in which a foreign body preadhered with the test strain was implanted subcutaneously, followed by injection of the test strain. All five species of staphylococci produced abscesses.Staphylococcus epidermidis,S.schleiferi, andS.lugdunensisyielded species means of 76–91% abscess formation; 80–100% of the infected foreign bodies and tissues were culture positive. These three species were more virulent thanS.warneriorS.hominis, which produced abscesses in 54 and 65% of mice, respectively; only 10–48% of the infected samples were culture positive. Transmission electron microscopy of pure cultures of selected strains showed that all species possessed glycocalyx. All species produced a variety of possible virulence factors, such as α and δ hemolysins, as well as the aggressins lipase and esterase. The production of exoenzymes did not always correlate with virulence as demonstrated by abscess formation in mice.Key words: coagulase-negative staphylococci,Staphylococcus lugdunensis,Staphylococcus schleiferi.

ISSN:0008-4166    

DOI:10.1139/m90-080

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Toxigenic and nontoxigenic strains ofVibrio cholerae01 occur in the natural aquatic environment. It is not clear whetherV.cholerae01 lose toxigenicity and become nontoxigenic during survival in the aquatic environment as a result of the effect of various biophysicochemical conditions (e.g., sunlight, pH, temperature, competition with other bacteria for nutrients, etc.). Five toxigenic strains were exposed to artificial aquatic environments in the presence of a filamentous green alga,Rhizoclonium fontanum, and recovered after different time intervals (0 and 0.5 h, 3, 6, 9, and 15 days). This experimental system was exposed to sunlight and theV.cholerae01 were in competition for nutrients with resident bacterial flora fromR.fontanum. The toxigenicity ofVibrio cholerae01 that were recovered at different time intervals was assessed by tissue culture assay using Vero cells. The toxigenicity of recovered strains was compared with that of the parent strains. The results demonstrated that toxigenicV.cholerae01 are unlikely to lose their toxigenicity in aquatic environments as a result of the effects of various biophysicochemical conditions. These results are consistent with the hypothesis of environmental reservoirs ofV.cholerae.Key words:Vibrio cholerae01, toxigenicity, survival, environment, algae.

ISSN:0008-4166    

DOI:10.1139/m90-081

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Rhizobium meliloti, like many bacteria, accumulates elevated levels of glutamate when osmotically stressed. The biochemical basis for this increase in glutamate production was investigated. Enzymes involved in glutamate synthesis, including glutamine synthetase, glutamate synthase, and glutamic dehydrogenase, were characterized in dialyzed crude cell-free extracts. A transaminase activity, which uses branched chain amino acids for the amination of 2-ketoglutaric acid, was also characterized. With the exception of glutamic dehydrogenase, the specific activity of the enzymes did not vary more than 4-fold in response to the available source of nitrogen or supplemental glutamate. Glutamic dehydrogenase activity was 13-fold greater when cells grew with 10 mMthan when cells grew with 0.5 mM. Glutamate synthase was repressed 2-fold when cells grew with supplemental glutamate. Conversely, this enzyme was derepressed 2× when cells grew with 0.5 mMor nitrate. Growing cells in minimal defined medium with 400 mM NaCl to cause osmotic stress had little effect on the specific activity of any of the enzymes. The addition of K+to the reactions stimulated heat-stable glutamine synthetase activity, but inhibited the other enzymes. Glutamate synthase was inhibited to a limited extent by several intermediates in the Krebs' cycle and very severely by glyoxylate. The addition of 10 mM glutamate to the reaction inhibited glutamate synthase 20%, but had no effect on the other enzymes.Key words: enzymes, glutamate synthesis, osmotic stress.

ISSN:0008-4166    

DOI:10.1139/m90-082

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The influence of selenite on the growth of bacterioplankton present in samples of three lakes was analyzed; these samples were collected in sulfate-rich, oligotrophic Lake Banyoles, moderately eutrophic Lake Erken, and hypereutrophic Lake Vallentunasjön. Experiments were set up in a completely randomized factorial design to analyze the effect of selenite alone and, in the same experiment, the effect of selenite in the presence of phosphate. Cultures of bacterioplankton, free of algae and zooplankton, diluted with filtered natural water, were used in the bioassays. The addition of 100 μg P∙L−1to samples from Lake Banyoles, collected during the winter, enhanced cell yield 2.7 times; the addition of 10 μg P∙L−1to samples from Lake Erken, collected during the spring, doubled the yield. Strong effects of phosphate on growth rates were found in samples from lakes Banyoles and Vallentunasjön. When bacteria from Lake Banyoles were exposed to 100 μg P∙L−1, the specific growth rate was 0.08 h−1(log units), compared with 0.03 h−1in the control. In spring, Lake Vallentunasjôn contained water with a considerable amount of dissolved organic phosphorus (18 μg P∙L−1); the addition of 100 μg P∙L−1, in the form of phosphate, resulted in a shorter lag phase of at least 48 h and reduced the specific growth rate to about half that in the control. Selenite had a significant positive effect on cell yield in samples from lakes Banyoles (p = 0.0001) and Vallentunasjön (p = 0.020), whereas the effect on cell yield in samples from Lake Erken was slightly negative (p = 0.110). The addition of selenite alone (550 ng Se∙L−1) to samples from Lake Banyoles, collected during the summer, doubled the biovolume of bacterioplankton within 37 h. Among winter bacteria from Lake Banyoles, selenite, at concentrations of 55 and 550 ng Se∙L−1, increased the number of bacteria twofold and threefold, respectively, but only when the phosphate level was high (100 μg P∙L−1). A high inorganic phosphorus level of 100 μg P∙L−1was also necessary to stimulate the effect of selenite on bacterial growth in samples from Lake Vallentunasjön; 550 ng Se∙L−1enhanced cell yield 24%. The negative effect of selenite on samples from Lake Erken was most obvious when phosphate (10 or 100 μg P∙L−1) had been added simultaneously (p = 0.030 for selenium and phosphorus interaction). Cell yields were always greater at the highest temperature. With samples from Lake Vallentunasjön, selenite stimulated bacterial growth at 25 °C but had no effect at 10 °C. With samples from Lake Banyoles, the simultaneous addition of phosphate and selenite increased cell yield threefold at 15 °C and only twofold at 30 °C.Key words: phosphorus, sulfate, Lake Erken, Lake Vallentunasj&

ISSN:0008-4166    

DOI:10.1139/m90-083

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Aqueous suspensions of conidia ofGliocladium virensstrains Gl-3 and Gl-21 were exposed to both ultraviolet radiation and ethyl methanesulfonate. Two mutants of Gl-3 and three of Gl-21 were selected for tolerance to benomyl at 10 μg∙mL−1, as indicated by growth and conidial germination on benomyl-amended potato dextrose agar. The mutants differed considerably from their respective wild-type strains in appearance, growth habit, sporulation, carbon-source utilization, and enzyme activity profiles. Of 10 carbon sources tested, cellobiose, xylose, and xylan were the best for growth, galactose and glucose were intermediate, and arabinose, ribose, and rhamnose were poor sources of carbon. The wild-type strains and the mutants did not utilize cellulose as the sole carbon source for growth. Two benomyl-tolerant mutants of Gl-3 produced less cellulase (β-1,4-glucosidase, carboxymethylcellulase, filter-paper cellulase) than Gl-3. In contrast, mutants of Gl-21 produced more cellulase than the wild-type strain. Only Gl-3 provided control of blight on snapbean caused bySclerotium rolfsii. Wild-type strain Gl-21 and all mutants from both strains were ineffective biocontrol agents.Key words:Gliocladium, benomyl tolerance,Sclerotium, rhizosphere competenc

ISSN:0008-4166    

DOI:10.1139/m90-084

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Alkaline sucrose gradient sedimentation was used to establish whether strand breakage and repair take place in the DNA of UV-irradiatedBacteroides fragilisduring the removal of pyrimidine dimers. AB.fragiliswild-type strain and two of its repair mutants, a mitomycin C sensitive mutant (MTC25) having wild-type levels of UV survival, and a UV-sensitive, mitomycin C sensitive mutant (UVS9), were investigated. Under anaerobic conditions, far-UV irradiation induced metabolically regulated strand breakage and resynthesis in the wild-type strain, but this was markedly reduced in both the MTC25 and UVS9 mutants. Approximately half of the strand breaks generated by the various strains were rejoined during further holding in buffer. Under replicating conditions, complete repair of strand breaks in the wild type was observed. Caffeine treatment under anaerobic conditions caused direct DNA strand breakage inB.fragiliscells but did not inhibit UV-induced breakage or repair.Key words:Bacteroides fragilis, DNA breakage, DNA repair, caffeine.

ISSN:0008-4166    

DOI:10.1139/m90-085

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

3-Phenoxybenzoic acid is an intermediate in the degradation of several pyrethroid insecticides in soil. Two pseudomonads were isolated together on vitamin-supplemented nutrient agar from 3-phenoxybenzoate enrichment of an agricultural soil. One isolate, designated 13b, grew on 3-phenoxybenzoate in mineral salts medium producing stoichiometric amounts of phenol. It degraded 3-[phenoxy-14C(U)]phenoxybenzoate to [14C(U)]phenol and did not assimilate any14C from this molecule. It metabolized [carboxyl-14C]3-phenoxybenzoate but not [14C(U)]phenol. It also produced 4-chlorophenol andp-cresol from 3-(4-chlorophenoxy)benzoate and 3-(4-methylphenoxy)benzoate, respectively. This indicated that isolate 13btransformed the benzoate but not the phenoxy moiety of 3-phenoxybenzoate. The second isolate, designated 13a, did not metabolize 3-phenoxybenzoate but grew on and mineralized phenol. Incubation of 3-phenoxybenzoate with isolates 13aand 13btogether resulted in the degradation of both aromatic nuclei.Key words: 3-phenoxybenzoate, bacterial degradation, mineralization, pyrethroid.

ISSN:0008-4166    

DOI:10.1139/m90-086

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Solutions of methionine (1 mM) plus riboflavin (26.6 μM) (MR mixture) in the presence of light are toxigenic to a wide spectrum of microorganisms.Agrobacterium tumefaciensandVerticillium dahliaeare representative of these microorganisms and were used in this study. The biocidal activity of the MR mixture was significantly enhanced when aerated or supplemented with Cu2+or Fe2+ions; the increased toxicity suggested the involvement of the O2−-driven Haber–Weiss reaction, from which the associated production and reactivity of O2−, H2O2, and1O2may have contributed to the biocidal activity. Although the presence of EDTA did not lessen the toxicity of the MR mixture, the addition of butylated hydroxyanisole effectively quenched its biocidal activity. Supplementation of MR mixture with antioxidants like α-tocopherol and β-carotene also was effective in reducing its biocidal activity and suggested further that the production of the above-mentioned oxygen species was critical for a photodynamic toxigenic reaction. In addition to the involvement of oxygen derivatives, the role of various methionine photodegradation products in the biocidal reaction was also evaluated. Methional and acrolein were among the methionine-derived components that were toxic. The highest amounts of methional and acrolein detected in the MR reaction system during an 8-h period by HPLC were approximately 46.5 and 10.6 μM, respectively. However, to achieve the toxicity equivalent to that of the MR mixture, the production of more than 5 mM methional or 100 μM acrolein would be necessary. Thus, the overall toxicity of the MR mixture appeared to be associated with the generation of highly reactive oxygen radicals.Key words: methionine–riboflavin mixture, photodynamic toxicity, methional, acrolein, activated oxygen derivatives,Agrobacterium tumefaciens,Verticillium dahliae.

ISSN:0008-4166    

DOI:10.1139/m90-087

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

Among 139Streptococcus mutansfresh isolates tested, using the deferred-antagonism test andStreptococcus sanguisNy 101 as the indicator strain, we observed that the frequency of detection of inhibition zones was reduced by 19% (from 53 to 34%) when arginine (1%) was used in the overlay agar. Among pigmented strains, the frequency of mutacin-like production was 70%. The frequency with which inhibition zones were detected varied from 7 to 91%, depending on the indicator strain used. These results indicate that the ability to detect the presence of mutacin-like substances varies widely and is dependent to a great extent on the methodology used.Key words: mutacin, bacteriocin, antagonism,Streptococcus mutans, inhibitory substance.

ISSN:0008-4166    

DOI:10.1139/m90-088

出版商:NRC Research Press    

年代:1990

数据来源: NRC

摘要:

The alkaline proteinase ofBrevibacterium linenswas partially purified through ultrafiltration and chromatography on Sephacryl S-200. The molecular weight of this enzyme was determined by gel electrophoresis in polyacrylamide to be 52 000 – 55 000. The proteinase hydrolyses natural polypeptides such as casein, haemoglobin, bovine serum albumin, and ovalbumin. An apparentKmfor casein was determined to be 1.3 mg∙mL−1. The optimal pH for caseinolytic activity was between 7.0 and 8.5 at the optimal temperature of 45 °C. The isolated enzyme is thermolabile: incubation at 50 °C destroyed proteolytic activity. Substrate proteins have a stabilizing effect. Our inhibition studies revealed that theB.linensproteinase belongs to the serine proteinase class.Key words:Brevibacterium linens, proteinase, purificatio

ISSN:0008-4166    

DOI:10.1139/m90-089

出版商:NRC Research Press    

年代:1990

数据来源: NRC