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Vibrio cholerae, the causative agent of Asiatic cholera, is a gram-negative motile bacterial species acquired via oral ingestion of contaminated food or water sources. Cholera has spread from the Indian subcontinent where it is endemic to involve nearly the whole world seven times during the past 185 years. V. cholerae serogroup O1, biotype El Tor, has moved from Asia to cause pandemic disease in Africa and South America during the past 35 years. A new serogroup, O139, appeared in south Asia in 1992, has become endemic there, and threatens to start the next pandemic. The facultative human pathogen V. cholerae represents a paradigm that evolved from environmental non-pathogenic strains by acquisition of virulence genes. The major virulence factors of V. cholerae, cholera toxin (CTX) encoded by the ctxAB genes residing in the genome of filamentous lysogenic bacteriophage (CTXɸ) and toxin coregulated pilus (TCP) encoded by vibrio pathogenicity island (VPI). CTX, a potent stimulator of adenylate cyclase, causes the intestine to secrete watery fluid rich in sodium, bicarbonate, and potassium, in volumes far exceeding the intestinal absorptive capacity, by ADP-ribosylation of the alpha subunit of the GTP-binding protein. Thus intestinal infection with V. cholerae results in the loss of large volumes of watery stool, leading to severe and rapidly progressing dehydration and shock. Without adequate and appropriate rehydration therapy, severe cholera kills about half of affected individuals. Today, cholera still remains a burden mainly for underdeveloped countries, which cannot afford to establish or to maintain necessary hygienic and medical facilities. During the last three decades, intensive research has been undertaken to unravel the virulence properties and to study the epidemiology of this significant human pathogen. This review provides an overview of the role of CTX in the occurrence of this disease in humans.
The influence of the presence of bacteriophage ZD5, temperature, pH and the interaction of these factors on survival of Y. enterocolitica cells in pond water and buffers was examined. The presence of bacteriophage ZD5 and temperature have substantial influence on survival of Y. enterocolitica cells in buffers with different pHs. The statistical analysis showed a significant influence of the presence of phage ZD5 on the decrease in the number of Y. enterocolitica cells incubated in buffers with pHs 6, 7, and 8. In the presence of phage ZD5, pH itself turned out to be of no significance because the average numbers of Y. enterocolitica cells obtained in pHs 6, 7, and 8 did not differ significantly at p≤0.05. Statistical analysis confirms significant influence of the presence of phage ZD5 on the reduction of the number of Y. enterocolitica cells in pond water at both 4°C and 20°C. The lowest average value of the number of cells was obtained at 4°C in the presence of phage ZD5, both in the tested buffers and in the pond water.
Bacteriophages (phages) are bacterial viruses that interact with bacterial walls and invade bacterial cells. Moreover, they disturb bacterial metabolism and lead to bacteria lysis. In the case of Gram-negative bacteria crude phage cultures, apart from the phages themselves, the bacterial debris, bacterial proteins and nucleic acids contain endotoxins. These endotoxins (lipopolysaccharides) posses a high degree of toxicity in vitro and in vivo, and their removal is essential for safety in antibacterial bacteriophage therapy. An effective, scaleable purification of bacteriophages from endotoxins was accomplished by sequential ultrafiltration through polysulfone membrane (30 nm) followed by chromatography on sepharose 4B and Matrex Cellulofine Sulfate. The phage fraction after gel filtration chromatography routinely contained endotoxins in the 150-2500 EU/mL range. The procedure yielded bacteriophages contaminated with as little as 0.4-7 EU/ml (Limulus assay). This value lies within the permitted level for intravenous applications (5 EU/kg/h by European Pharmacopoeia, 1997)
The aim of this investigation was to reveal the regulatory properties of bacteriophage preparations in a model of mitogen-induced splenocyte proliferation in mice. We showed that sepharose 4B-purified preparations of the Staphylococcus aureus phage A20/R exhibited costimulatory activity in splenocyte proliferation induced by suboptimal (0.25 μg/ml) concentrations of ConA. On the other hand, the purified phage fraction was regulatory with regard to splenocyte proliferation induced by the optimal (2.5 μg/ml) ConA concentration. We also showed that the phage preparation can elicit IL-6 production in splenocyte cultures and enhance ConA-induced production of that cytokine. Furthermore, the phages preferentially induced IL-6 production in adherent splenocytes and increased levels of that cytokine in cultures of peritoneal cells from mice and rats. This phenomenon may explain the costimulatory activity of phages in the model described.
To get clues about the genes as well as the gene regulatory circuit controlling the lytic development of temperate mycobacteriophage L1, previously we screened several conditional lethal mutants of L1 and characterized some of them to an extent. One of the mutants, L1 G23ts23, was found defective in both growth and late gene transcription at 42°C but not at 32°C. Here we show that the above phage mutant is also defective in the expression of phage-coded deoxyribonuclease (DNase) at 42°C but not at 32°C. The G23 gene however does not code for the above enzyme. Further analyses using the L1 G23ts23 mutant suggest that synthesis of DNase is also not regulated by G23 at transcriptional level. Expression of functional DNase in fact requires de novo protein synthesis. Among the 25 revertants isolated from the L1 G23ts23 mutant, which are capable of growing at 42°C (by overcoming the ts defect in late transcription), two, R4 and R22, have been shown to retain the ts defect in the expression of the above enzyme and R4, to retain also the G23ts23 mutation. This suggests that R4 (R22 was not tested for the presence of G23ts23 mutation) carries an extragenic suppressor of G23ts23 mutation in a different gene (we call this putative gene as Gx), which now helps bypass the requirement of G23 for late gene transcription. Possible role of G23 on the regulation of L1-coded Gx and deoxyribonuclease has been discussed at length.
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The minimal genome paradox

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Expression of the replication genes of bacteriophage λ, O and P, is believed to be translationally coupled. However, it was previously noted that, under conditions of amino acid starvation, when O is not synthesized, P continues to be expressed at a relatively high level. The results presented in this report, contrary to the previously presented hypothesis, suggest that an AGACUGGAU sequence (an optimal context for translation initiation from non-AUG codons in eukaryotes, and present upstream the P cistron) is inactive in Escherichia coli. Comparative sequence analysis confirms that such a signal is unlikely to be important for P synthesis. Instead, a weak Shine-Dalgarno sequence may be present upstream the P cistron, and be active in the absence of O gene expression.
In this study we determined Vi bacteriophage III sensitivity to native cisplatin, γ radiation (60Co) or to irradiated cisplatin, and checked the possibility of enhanced Vi bacteriophage III inactivation under combined exposure to cisplatin and γ radiation. We used highly purified phage suspensions in 0.9% NaCl solution or phosphate-buffered saline. Phage suspensions were titrated using a double agar layer method. Our study implies that survival of Vi bacteriophage III shows an exponential inverse correlation with cisplatin concentration in the incubation medium and the time of phage incubation in the presence of cisplatin. The use of irradiated cisplatin reduces phage survival in comparison with suspensions containing non-irradiated cisplatin. Irradiation of phage suspension with cisplatin causes a significant increase of phage inactivation in comparison with either treatment alone. Our results suggest that presence of cisplatin in irradiated medium enhances the radiobiological effect on Vi bacteriophages III.
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