1,720,958 research outputs found
β-Lactamase induction antagonizes β-lactam susceptibilities in Citrobacter diversus and Enterobacter cloacae clinical isolates
No full textInducible β-lactamases were obtained after exposure to several β-lactams in clinical isolates of Enterobacter cloacae and Citrobacter diversus. Enzyme production was related to the inducer and medium composition. β-lactamase is able to inactivate only labile compounds, thus generating minimum inhibitory concentrations higher than in the absence of the inducer; imipenem susceptibilities usually were not changed
Citrobacter diversus ULA27 produces two forms of a chromosomal β-lactamase
No full textA multi-resistant clinical isolate of Citrobacter diversus, particularly resistant to penicillins and cephalosporins, has been studied. The strain produced constitutively high levels of β-lactamase which efficiently hydrolysed cephaloridine but not ampicillin. The apparent Km value for cephaloridine (125±25μM) was within the range usually observed for β-lactamases in similar bacteria. The strain possessed two forms of the enzyme as indicated by isoelectric focusing patterns, HPLC analysis and two pH optima. SDS-PAGE analysis indicated a single protein responsible for both forms. The strain possessed a single plasmid, as revealed by agarose gel electrophoresis, but β-lactamase production was not plasmid encoded. The available data indicate the β-lactamase(s) of C.diversus ULA27 to be chromosomally encoded. © 1987 The British Society for Antimicrobial Chemotherapy
On the kinetic interaction between ceftriaxone and some β-lactamases
No full textThe activity of β-lactamases from Citrobacter diversus ULA-27 on ceftriaxone, a widely recognized third-generation cephalosporin, has been examined and compared to the activity of various other β-lactamases from different sources. Ceftriaxone (Roche S.p.A. Milan) was found to be resistant to hydrolysis by β-lactamases from Enterobacter cloacae and Bacillus cereus, but susceptible to β-lactamases from Mycobacterium fortuitum strain Cow 18 and, mostly, to β-lactamases from various strains of Citrobacter diversus. Derivatives with substituents in the 3-position of ceftriaxone, namely cefotaxime (Roussel Maestretti S.p.A., Milan) and ceftizoxime (Farmitalia Carlo Erba, Milan), were much less susceptible to hydrolysis by C. diversus ULA-27 enzymes (22 and 6% of ceftriaxone hydrolysis, respectively), the hydrolysis rate being paralleled by differences in MIC values. Ceftriaxone inhibited the activity of E. cloacae β-lactamases toward cefazolin as substrate, but the inhibition was totally abolished by preincubation of ceftriaxone with the enzyme before addition of the substrate. Overall, the data point to a relevance of C. diversus ULA-27 β-lactamases in the mechanism of resistance of this strain to the various third-generation cephalosporins
Broad spectrum β-lactamases of citrobacter diversus
No full textCitrobacter diversus NF85 produced a chromosomal β-lactamase that was induced by a variety of β-lactam antibiotics. Two major forms of the enzyme, with isoelectric points (pI's) of 5·7 and 6·2, were found in crude cell extracts. Derepressed mutants of NF85, generated by nitrosoguanidine treatment, displayed different levels of β-lactamase expression to the parent strain and had different patterns of resistance to a range of β-lactam antibiotics. Those mutants of NF85 that were totally derepressed, expressing high, constitutive levels of enzyme, were found to have an additional β-lactamase activity with a pI of 6·8. © 1990 by The British Society for Antimicrobial Chemotherapy
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Fractionation and characterization of two β-lactamases in Citrobacter diversus ULA-27 strain by chromatofocusing
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