1,720,958 research outputs found
Elementi genetici mobili in Streptococcus agalactiae: varietà, mobilità e contributo alla diffusione dell’antibiotico-resistenza.
No full textL’importanza clinica di Streptococcus agalactiae [β-haemolytic group B streptococci (GBS)], caratteristicamente associato a gravi infezioni neonatali, è andata aumentando negli ultimi decenni, sia in termini epidemiologici che di emergenza e diffusione della resistenza ad antibiotici di seconda linea, come macrolidi e lincosamidi.
Lo studio ha preso in considerazione 225 isolati clinici di GBS, allo scopo di valutarne la resistenza ai macrolidi e alla tetraciclina dal punto di vista sia fenotipico che molecolare, focalizzando l’attenzione sugli elementi genetici associati, soprattutto quelli definiti ‘elementi integrativi e coniugativi’ (ICE). Nell’ambito dei ceppi tetraciclino-resistenti sono stati individuati due trasposoni coniugativi che veicolano il gene tet(M): il ben noto e diffuso Tn916, e Tn5801, identificato in Staphylococcus aureus ma non ancora descritto in GBS. Dal momento che tale elemento è stato trovato in quasi un terzo dei ceppi analizzati, è stato caratterizzato in dettaglio e denominato Tn5801.Sag.
La distribuzione degli elementi genetici riscontrata tra i ceppi eritromicino-resistenti riflette la varietà degli ICE di S. agalactiae e suggerisce un interscambio genetico nell’ambito degli streptococchi.
Accanto ad elementi già noti anche in GBS, come Tn3872, sono stati identificati e caratterizzati nuovi ICE descritti in precedenza solo in S. pyogenes come (i) ICESp1116, responsabile della diffusione di erm(B), e (ii) ICE10750-RD.2, ICESp1108, e ICESp2907 che veicolano erm(TR). Quest’ultimo, in particolare, è stato designato ICE2907.Sag poiché era associato a un diverso elemento mosaico. Sono stati evidenziati anche nuovi elementi genetici la cui caratterizzazione è in corso.
Lo studio è stato completato valutando la trasferibilità degli elementi individuati mediante esperimenti di coniugazione.
Questi dati sottolineano l’importanza degli ICE nella variabilità genetica dei differenti isolati di S. agalactiae ed evidenziano il contributo dello scambio genico orizzontale nell’evoluzione del suo genoma e nell’adattamento all’ambiente
Characterization of Tn5801.Sag, a variant of Staphylococcus aureus Tn916 family transposon Tn5801 that is widespread in clinical isolates of Streptococcus agalactiae
No full textTn5801, originally detected in Staphylococcus aureus Mu50, is a Tn916 family element in which a unique int gene (int5801) replaces the int and xis genes in Tn916 (int916 and xis916). Among 62 tet(M)-positive tetracycline-resistant Streptococcus agalactiae isolates, 43 harbored Tn916, whereas 19 harbored a Tn5801-like element (Tn5801.Sag,-20.6 kb). Tn5801.Sag was characterized (PCR mapping, partial sequencing, and chromosomal integration) and compared to other Tn5801-like elements. Similar to Tn5801 from S. aureus Mu50, tested in parallel, Tn5801.Sag was unable to undergo circularization and conjugal transfer
A new mosaic integrative and conjugative element from Streptococcus agalactiae carrying resistance genes for chloramphenicol (catQ) and macrolides [mef(I) and erm(TR)]
No full textObjectives: To investigate the genetic basis of catQ-mediated chloramphenicol resistance in Streptococcus
agalactiae.
Methods: Two clinical strains of catQ-positive chloramphenicol-resistant S. agalactiae (Sag236 and Sag403) were
recently isolated, typed (MLST, PFGE pulsotypes, capsular types) and their antibiotic resistances investigated by
phenotypic and genotypic approaches. Several molecular methods (PCR mapping, restriction assays, Southern
blotting, sequencing and sequence analysis, conjugal transfer assays) were used to determine the genetic
context of catQ and characterize a genetic element detected in the isolates.
Results: Sag236 and Sag403 shared the same ST (ST19), but exhibited a different capsular type (III and V,
respectively) and pulsotype. Both harboured the macrolide resistance genes mef(I) and erm(TR) and the
tetracycline resistance gene tet(M). Accordingly, they were resistant to chloramphenicol, erythromycin and tetracycline.
catQ and mef(I) were associated in an IQ module that was indistinguishable in Sag236 and Sag403. In
mating assays, chloramphenicol and erythromycin resistance proved transferable, at low frequency, only from
Sag236. Transconjugants carried not only catQ and mef(I), but also erm(TR), suggesting a linkage of the three
resistance genes in a mobile element, which, though seemingly non-mobile, was also detected in Sag403. The
new element (designated ICESag236, 110 kb) results from recombination of two integrative and conjugative
elements (ICEs) originally described in different streptococcal species: S. agalactiae ICESagTR7, carrying erm(TR);
and Streptococcus pneumoniae ICESpn529IQ, carrying the prototype IQ module.
Conclusions: These findings strengthen the notion that widespread streptococcal ICEs may form mosaics that
enhance their diversity and spread, broaden their host range and carry new cargo genes
ICESp1116, the genetic element responsible for erm(B)-mediated, inducible resistance to erythromycin in Streptococcus pyogenes
No full textICESp1116, responsible for erm(B)-mediated, inducible erythromycin resistance in Streptococcus pyogenes, was comprehensively characterized, and its chromosomal integration site was determined. It displayed a unique mosaic organization consisting of a scaffold, related to TnGallo1 from Streptococcus gallolyticus, with two inserted fragments separated by IS1216. One fragment, containing erm(B), displayed high-level identity to a portion of the S. pyogenes plasmid pSM19035; the other, containing a truncated tet(M) gene, displayed high-level identity to the right-hand portion of Clostridium difficile Tn5397
Tn5253 family integrative and conjugative elements carrying mef(I) and catQ determinants in Streptococcus pneumoniae and Streptococcus pyogenes
No full textThe linkage between the macrolide efflux gene mef(I) and the chloramphenicol inactivation gene catQ was first described in Streptococcus pneumoniae (strain Spn529), where the two genes are located in a module designated IQ element. Subsequently, two different defective IQ elements were detected in Streptococcus pyogenes (strains Spy029 and Spy005). The genetic elements carrying the three IQ elements were characterized, and all were found to be Tn5253 family integrative and conjugative elements (ICEs). The ICE from S. pneumoniae (ICESpn529IQ) was sequenced, whereas the ICEs from S. pyogenes (ICESpy029IQ and ICESpy005IQ, the first Tn5253-like ICEs reported in this species) were characterized by PCR mapping, partial sequencing, and restriction analysis. ICESpn529IQ and ICESpy029IQ were found to share the int(Sp23FST81) integrase gene and an identical Tn916 fragment, whereas ICESpy005IQ has int(5252) and lacks Tn916. All three ICEs were found to lack the linearized pC194 plasmid that is usually associated with Tn5253-like ICEs, and all displayed a single copy of a toxin-antitoxin operon that is typically contained in the direct repeats flanking the excisable pC194 region when this region is present. Two different insertion sites of the IQ elements were detected, one in ICESpn529IQ and ICESpy029IQ, and another in ICESpy005IQ. The chromosomal integration of the three ICEs was site specific, depending on the integrase (int(Sp23FST81) or int(5252)). Only ICESpy005IQ was excised in circular form and transferred by conjugation. By transformation, mef(I) and catQ were cotransferred at a high frequency from S. pyogenes Spy005 and at very low frequencies from S. pneumoniae Spn529 and S. pyogenes Spy029
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
Genetic basis of the association of resistance genes mef(I) (macrolides) and catQ (chloramphenicol) in streptococci
No full textIn streptococci mef(I) and catQ, two relatively uncommon macrolide and chloramphenicol resistance genes, respectively, are typically linked in a genetic module designated IQ module. Though variable, the module consistently encompasses, and is sometimes reduced to, a conserved ~5.8-kb mef(I)-catQ fragment. The prototype IQ module was described in Streptococcus pneumoniae. IQ-like modules have subsequently been detected in Streptococcus pyogenes and in different species of viridans group streptococci, where mef(E) may be found instead of mef(I). Three genetic elements, one carrying the prototype IQ module from S. pneumoniae and two carrying different, defective IQ modules from S. pyogenes, have recently been characterized. All are integrative and conjugative elements (ICEs) belonging to the Tn5253 family, and have been designated ICESpn529IQ, ICESpy029IQ and ICESpy005IQ, respectively. ICESpy029IQ and ICESpy005IQ were the first Tn5253 family ICEs to be described in S. pyogenes. A wealth of new information has been obtained by comparing their genetic organization, chromosomal integration, and transferability. The origin of the IQ module is unknown. The mechanism by which it spreads in streptococci is 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
- …
