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ETEROGENEITA’ DI ELEMENTI CONIUGATIVI INTEGRATIVI IN ISOLATI CLINICI DI STREPTOCOCCUS PNEUMONIAE
No full textNew Tn916-related elements causing erm(B)-mediated erythromycin resistance in tetracycline-susceptible pneumococci
Full text linkAbstract
OBJECTIVES:
To analyse the as yet unexplored genetic elements encoding erm(B)-mediated erythromycin resistance in tetracycline-susceptible pneumococci.
METHODS:
Sixteen Streptococcus pneumoniae clinical isolates sharing erm(B)-mediated erythromycin resistance and susceptibility to tetracycline were used. Gene detection was performed by PCR using both established and specially designed primers. S. pneumoniae R6, Streptococcus pyogenes 12RF and Enterococcus faecalis JH2-2 were used as recipients in mating experiments.
RESULTS:
Of the 16 test strains, 14 bore an unexpressed tet(M) gene which in 13 strains had a genetic linkage with erm(B). Three isolates yielded a 3.2 kb and 10 an 11.9 kb erm(B)/tet(M) amplicon. The former three showed genetic organizations similar to that of the composite element Tn3872, where the erm(B)-carrying Tn917 transposon is inserted into a Tn916-like element. Of the latter 10 isolates, 9 showed genetic organizations substantially overlapping with that of Tn6002, a newly sequenced erm(B)-containing Tn916-related transposon. The tenth isolate carried a novel composite element (designated Tn6003) resulting from the insertion into a Tn6002-like transposon of a fragment [designated macrolide-aminoglycoside-streptothricin (MAS) element] containing a second erm(B) (lacking the stop codon) and a variant of the aadE-sat4-aphA-3 cluster. The two tet(M)-negative isolates had different Tn3872-related elements, one containing a complete and one a deleted MAS fragment. Conjugative transfer was obtained from donors carrying Tn6002-related elements, not from donors carrying Tn3872-related elements.
CONCLUSIONS:
In tetracycline-susceptible pneumococci with erm(B)-mediated erythromycin resistance, the erm(B) gene is carried on a variety of Tn916-related genetic elements either lacking tet(M) or, more often, carrying an unexpressed tet(M) gene
Genetic determinants and elements associated with antibiotic resistance in viridans group streptococci
No full textNew Tn916-related elements causing erm(B)-mediated erythromycin resistance in tetracycline-susceptible pneumococci
No full textObjectives: To analyse the as yet unexplored genetic elements encoding erm(B)-mediated erythromycin
resistance in tetracycline-susceptible pneumococci.
Methods: Sixteen Streptococcus pneumoniae clinical isolates sharing erm(B)-mediated erythromycin
resistance and susceptibility to tetracycline were used. Gene detection was performed by PCR using
both established and specially designed primers. S. pneumoniae R6, Streptococcus pyogenes 12RF
and Enterococcus faecalis JH2–2 were used as recipients in mating experiments.
Results: Of the 16 test strains, 14 bore an unexpressed tet(M) gene which in 13 strains had a genetic
linkage with erm(B). Three isolates yielded a 3.2 kb and 10 an 11.9 kb erm(B)/tet(M) amplicon. The
former three showed genetic organizations similar to that of the composite element Tn3872, where the
erm(B)-carrying Tn917 transposon is inserted into a Tn916-like element. Of the latter 10 isolates, 9
showed genetic organizations substantially overlapping with that of Tn6002, a newly sequenced
erm(B)-containing Tn916-related transposon. The tenth isolate carried a novel composite element
(designated Tn6003) resulting from the insertion into a Tn6002-like transposon of a fragment [designated
macrolide–aminoglycoside–streptothricin (MAS) element] containing a second erm(B) (lacking
the stop codon) and a variant of the aadE–sat4–aphA-3 cluster. The two tet(M)-negative isolates had
different Tn3872-related elements, one containing a complete and one a deleted MAS fragment.
Conjugative transfer was obtained from donors carrying Tn6002-related elements, not from donors
carrying Tn3872-related elements.
Conclusions: In tetracycline-susceptible pneumococci with erm(B)-mediated erythromycin resistance,
the erm(B) gene is carried on a variety of Tn916-related genetic elements either lacking tet(M) or, more
often, carrying an unexpressed tet(M) gene
Molecular characterization of clinical Streptococcus pneumoniae isolates with reduced susceptibility to fluoroquinolones emerging in Italy
No full textEffects of fluoroquinolones on bacterial adhesion and on preformed biofilm of strains isolated from urinary double J stents.
No full text
erm(B)-Carrying Elements in Tetracycline-Resistant Pneumococci and Correspondence between Tn1545 and Tn6003
Full text linkAbstract
This study investigated the genetic organization of erm(B)-carrying transposons of Streptococcus pneumoniae and their distribution in tetracycline-resistant clinical isolates. By comparatively analyzing reference pneumococci carrying erm(B)/tet(M) transposon Tn1545, Tn6003, Tn6002, or Tn3872, we demonstrated a substantial correspondence between Tn1545 and Tn6003, which have the same resistance gene combination [tet(M) (tetracycline), erm(B) (erythromycin), and aphA-3 (kanamycin)]; share the macrolide-aminoglycoside-streptothricin element, containing a second erm(B); and only differ by a ca. 1.2-kb insertion (containing a putative IS1239 insertion sequence) detected in Tn1545 from S. pneumoniae reference strain BM4200. These results enabled elucidation of the structure of Tn1545, the first erm(B)-carrying transposon described in S. pneumoniae. A collection of 83 erythromycin- and tetracycline-resistant clinical pneumococci, representative of recent Italian isolates carrying erm(B) as the sole erythromycin resistance gene, was used to investigate the distribution of the different transposons. All 83 organisms were positive for tet(M) and bore an erm(B)/tet(M) transposon that could be characterized by using a specific set of primer pairs; Tn3872 was detected in 18 isolates, Tn6002 in 59 isolates, and Tn6003 in 6 (the sole kanamycin-resistant) isolates. The genetic organization of transposon Tn1545, with its specific insertion, was not detected in any of the isolates tested. The erm(B)-carrying elements of tetracycline-resistant pneumococci substantially corresponded to those [bearing a silent tet(M) gene] recently detected in tetracycline-susceptible pneumococci. Overall, in erm(B)-positive pneumococci, Tn6003 was the least common erm(B)-carrying Tn916-related element and Tn6002 the most common
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
Heterogeneity of Tn5253-Like Composite Elements in Clinical Streptococcus pneumoniae Isolates.
No full textSeveral drug resistances in Streptococcus pneumoniae are associated with mobile genetic elements, which are loosely subdivided into a group of smaller (18- to 27-kb) and a group of larger (>50-kb) elements. While the elements of the former group, which typically carry the tetracycline resistance determinant tet(M) and whose prototype is Tn916 (18 kb), have been studied extensively, the larger elements, whose prototype is Tn5253 (∼65.5 kb), are not as well explored. Tn5253 is a composite structure consisting of two independent conjugative transposons, Tn5251 (which is virtually identical to Tn916) and Tn5252 (∼47.5 kb), with the former inserted into the latter. Tn5252, which so far has only partially been sequenced, carries an integrase gene, driving its site-specific insertion into the host cell genome, and the chloramphenicol resistance cat(pC194) determinant. This study investigated 20 clinical isolates of S. pneumoniae, which were selected on the basis of cat(pC194)-mediated chloramphenicol resistance. All 20 isolates harbored a Tn5253-like element. The composite elements (some of which have been completely sequenced) demonstrated considerable heterogeneity that stemmed from a dual variability: in the Tn5252-like element, due primarily to differences in the integrase gene but also to differences in cargo genes and in the overall genetic organization, and in the Tn916-like element, with the possible involvement, besides Tn916, of a number of Tn916 family pneumococcal elements carrying different erythromycin resistance genes. In mating experiments, only one composite element, containing a less typical Tn916 family element, appeared to be nonmobile. Being part of a Tn5253-like composite element may confer on some Tn916-like transposons, which are apparently nontransferable as independent genetic elements, the ability to be mobilized
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