ISSN:0008-4166    

DOI:10.1139/cjmcontents99

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The beneficial effect of lactobacilli has been attributed to their ability to colonize human and animal gastrointestinal tracts. In this work, adhesion assays with three lactobacillus strains and intestinal fragments obtained from chickens were assessed.Lactobacillus animalisandL. fermentumwere able to adhere to three kinds of epithelial cells (crop, small and large intestines) with predominance to small intestine. Among the strains considered,L. fermentumsubsp.cellobiosusshowed the lowest andL. animalisthe highest adhesion ability. Scanning electron microphotographs showingL. animalisandL. fermentumadhering to intestinal cells were obtained. The characterization ofL. animalisadhesion indicated that lectin-like structure of this strain has glucose/mannose as specific sugars of binding. However, a calcium requirement was not observed. The adhesion ofL. fermentumwas reduced by addition of sialic acid or mannose (P< 0.01). These carbohydrates can be involved in the interaction between adhesin and epithelial surface. In this case, the dependence on bivalent cations was demonstrated.Lactobacillus fermentumwas effective in reducing the attachment ofSalmonella pullorumby 77%, whileL. animaliswas able to inhibit (90%, 88%, and 78%) the adhesion ofS. pullorum,S. enteritidis, andS. gallinarumto host-specific epithelial fragments respectively. Our results from this in vitro model suggest that these lactobacilli are able to block the binding sites forSalmonellaadhesion.Key words: lactobacilli, lectin-like structures, poultry adhesion, probiotic properties.

ISSN:0008-4166    

DOI:10.1139/w99-102

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

For the first time, microcin-producing strains showing inhibitory activities against enteropathogenSalmonella enteritidiswere isolated from poultry intestinal contents. Among the numerous strains isolated, two strains ofEscherichia coli, named J02 and J03, showing the greatest activities againstS. enteritidis, were studied. Biochemical tests and purification identified the main antagonist compound produced as microcin J25. In order to evaluate the protective potential ofE. coliJ02 and J03 againstS. enteritidisinfection, the ability of these strains to inhibit growth ofS. enteritidiswas investigated in mixed culture. A strong antagonist activity was obtained with a preculture phase of the active strain in minimal medium before incubation withS. enteritidis. In a bioreactor experiment simulating the chicken gastric and intestinal tract environment, a mixture of the two strainsE. coliJ02 and J03, provided an enhanced inhibitory effect. Microcinogenic strain activities were not affected by bile, pancreatic enzymes addition, or acidic conditions. These results suggest the relevant role of microcin-producing microorganisms in microbial intestinal ecology. To conclude, this study shows that microcin J25 strains could exert a beneficial protective effect againstS. enteritidisgrowth in situ.Key words: microcin J25,Salmonella, mixed cultures.

ISSN:0008-4166    

DOI:10.1139/w99-106

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Acinetobacter baumanniiBL54, a silver (Ag) resistant micro-organism was isolated from clinical samples collected at the Armed Forces Medical College hospital in Pune, India. The strain BL54 removed a high quantity of silver (2.85 mg/g biomass) from photographic wastewater effluent. Treatment of the cells with 10 mM EDTA or agitating the culture did not affect the removal process, while altering pH of the wastewater or pre-treating the cells with 0.5 mM 2,4-dinitrophenol (DNP), 20 &mgr;M N,N'-dicyclohexylcarbodiimide (DCC), 25 &mgr;g/mL cefotaxime, and polymyxin-B resulted in considerable decrease in removal of silver by the organism. Dead cells, or a Agsplasmid-cured derivative (BL54.1) removed little silver, which was mainly surface bound. The results, compared with accumulation of Ag by a sensitive culture ofEscherichia coliK12 J53.2, suggest thatA. baumanniiBL54 has good potential for bioremediation of silver from photographic wastewater effluents.Key words:Acinetobacter, silver resistance, silver removal.

ISSN:0008-4166    

DOI:10.1139/w99-077

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Restriction fragment length polymorphism (RFLP) analysis was carried out for 136 natural isolates belonging to the familyVibrionaceae.These were collected from inshore areas of Japan, mainly in winter. Twenty-eight 16S rDNA genotypes were obtained by digestion with four restriction endonucleases (HhaI,DdeI,RsaI, andSau3AI). To estimate the genetic relationships, 53 informative fragments were scored by their presence or absence. A dendrogram was constructed using the unweighted pair group method with the arithmetic averages algorithm. Five RFLP groups (groups I to V) were obtained. Group I corresponded toVibrio splendidus-like strains. It was confirmed that this group was not only found in Otsuchi Bay, but also in broad coastal areas of Japan. Group II strains were not identified as previously knownVibriospecies. Group III strains were regarded as members of theVibriomain group, which is a major phylogenetic group deduced from 16S rRNA gene analysis in the familyVibrionaceae. The RFLP profile indicated that Group IV strains were closely related toV. hollisae. Group V strains showed RFLP patterns which have not been observed previously. From the clustering analysis, it was concluded that group V strains were notVibriospecies. Most of the isolates studied were not identified as previously described species. It suggests that many psychrotrophic vibrios in cold marine environments remain as unknown species.Key words:Vibrio, vibrios, psychrotroph, restriction fragment length polymorphism (RFLP) analysis,Vibrio splendidus.

ISSN:0008-4166    

DOI:10.1139/w99-105

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The expression of thetoxAandregAgenes inPseudomonas aeruginosais negatively regulated by iron at the transcriptional level. We have previously describedptxR, an exotoxin A regulatory gene which appears to enhancetoxAexpression throughregA. In this study, we have tried to determine ifptxRexpression correlates with its effect ontoxAandregAexpression throughout the growth cycle ofP. aeruginosastrain PAO1. This was done using Northern blot hybridization experiments (withtoxA, regA, andptxRprobes), andptxRtranscriptional fusion studies. To avoid problems related to the presence of multiple copies ofptxRin PAO1, we have constructed a PAO1 strain (PAO1-XR) that carries only twoptxRgenes in its chromosome. Our results showed that when PAO1-XR was grown in iron-limited conditions, the increase in exotoxin A activity and the accumulation oftoxAmRNA appeared at about mid- to late-exponential phase. A similar increase in the accumulation ofregAmRNA was detected. BothregAtranscripts, T1 and T2, were enhanced in PAO1-XR. In iron-sufficient medium, neithertoxAnorregAmRNA was detected at any time point in the growth cycle of PAO1-XR. In contrast, the accumulation ofptxRmRNA was detected throughout the growth cycle of PAO1-XR under both iron-deficient and iron-sufficient conditions. The presence of iron in the growth medium also had no effect on the level of &bgr;-galactosidase activity produced by aptxR-lacZfusion in PAO1. These results suggest that (i) the enhancement intoxAexpression byptxRcorrelates with the enhancement inregAexpression; (ii)ptxRaffects the expression of theregAP1 and P2 promoters; (iii)ptxRexpression precedes its effect ontoxAandregAexpression; and (iv) unliketoxAandregA, the overall expression ofptxRthroughout the growth cycle of PAO1 is not negatively regulated by iron.Key words:ptxR, differential expression, transcriptional regulation,regA,toxA.

ISSN:0008-4166    

DOI:10.1139/w99-103

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

Lipopolysaccharide (LPS) has previously been identified as the major adhesin ofActinobacillus pleuropneumoniaeinvolved in adherence to porcine respiratory tract cells. The purpose of the present study was to isolate and characterize mutants in LPS biosynthesis by using a mini-Tn10transposon mutagenesis system. Seven mutants appeared to possess a rough LPS (among which two had similar Southern blot profiles) while one mutant (#5.1) expressed the high-molecular-mass LPS, but as visualized by Tricine SDS-PAGE, showed an additional band in the core-lipid A region. The LPS mutants showed sensitivity to pig serum to various degrees, while the parent strain was serum-resistant. Use of piglet frozen tracheal sections indicated that, surprisingly, the rough LPS mutants adhered similarly or in greater numbers than the parent strain. However, the LPS mutant #5.1 adhered significantly less than the parent strain and was also less virulent in pigs. The gene affected by mini-Tn10in LPS mutant #5.1 isgalU, the structural gene for UTP-&agr;-D-glucose-1-phosphate uridylyltransferase, involved in LPS core biosynthesis. Complementation analysis confirmed that the phenotypic characteristics of LPS mutant #5.1 are the result of the inactivation of thegalUgene. Our data suggest that although the presence of O-antigen does not seem to be essential, an intact core-lipid A region might be required for adherence ofA. pleuropneumoniaeto porcine respiratory tract cells. To the best of our knowledge, these mutants represent the first isogenic mutants ofA. pleuropneumoniaedefective in LPS biosynthetic genes.Key words:Actinobacillus pleuropneumoniae, lipopolysaccharides, mutant, adherence, virulence.

ISSN:0008-4166    

DOI:10.1139/w99-107

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

A complex medium supported good growth of the type strain ofStreptococcus suisirrespective of the presence or absence of a high concentration (1 mM) of the iron chelating agent, ethylenediamine di-o-hydroxyphenylacetic acid. Good growth was also obtained using a complex medium that had been treated with Chelex-100 to reduce the iron content, but only if this medium was supplemented with manganese; supplementation with iron had little effect. Collectively, these results indicate thatS. suisrequires manganese, but not iron, for growth. Polyacrylamide gel electrophoresis of cell extracts followed by activity staining revealed the presence of a single manganese-cofactored superoxide dismutase; activity staining and enzyme assays revealed that manganese availability during growth affected the activity of the superoxide dismutase in cell extracts. The results are discussed with respect to the capacity ofS. suisto avoid damage by reactive oxygen species.Key words:Streptococcus suis, iron, manganese, superoxide dismutase.

ISSN:0008-4166    

DOI:10.1139/w99-114

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

In response to low extracellular glucose concentration,Pseudomonas aeruginosainduces the expression of the outer membrane carbohydrate-selective OprB porin. The promoter region of theoprBgene was cloned into alacZtranscriptional fusion vector, and the construct was mobilized intoP. aeruginosaOprB-deficient strain, WW100, to evaluate additional environmental factors that influence OprB porin gene expression. Growth temperature, pH of the growth medium, salicylate concentration, and carbohydrate source were found to differentially influence porin expression. This expression pattern was compared to those of whole-cell [14C]glucose uptake under conditions of high osmolarity, ionicity, variable pH, growth temperatures, and carbohydrate source. These studies revealed that the high-affinity glucose transport genes are down-regulated by salicylic acid, differentially regulated by pH and temperature, and are specifically responsive to exogenous glucose induction.Key words:Pseudomonas aeruginosa, OprB porin, glucose transport, regulation.

ISSN:0008-4166    

DOI:10.1139/w99-110

出版商:NRC Research Press    

年代:1999

数据来源: NRC

摘要:

The mRNA level insecgenes ofStreptomyces lividanswas studied as a function of growth temperature, glucose effect, and growth using two different carbon sources. Glucose and xylan, a complex hemicellulose, were used as carbon sources for the growth ofS. lividans. For both substrates, the mRNA levels ofsecA,secD,secE,secF, andsecYgenes were almost constant during the early and log phases, but showed a marked decrease at the beginning of the stationary phase followed by a full recovery of mRNA level in the late stationary phase. This indicates that thesecgenes are actively transcribed during the differentiation process. The mRNA level in xylan was generally from 1.5- to 2-fold that in glucose. At growth temperatures of 28°C, 34°C, or 40°C, there was no significant difference in thesecgene mRNA levels.Key words:Streptomyces lividans,secgenes, glucose repression, growth-phase dependent expressi

ISSN:0008-4166    

DOI:10.1139/w99-091

出版商:NRC Research Press    

年代:1999

数据来源: NRC