Characterization of Tn5801.Sag, a variant of Staphylococcus aureus Tn916 family transposon Tn5801 that is widespread in clinical isolates of Streptococcus agalactiae.

Tn5801, 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.

Heterogeneity of Tn5253-like composite elements in clinical Streptococcus pneumoniae isolates.

Several 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.

erm(B)-carrying elements in tetracycline-resistant pneumococci and correspondence between Tn1545 and Tn6003.

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.

Composite structure of Streptococcus pneumoniae containing the erythromycin efflux resistance gene mefI and the chloramphenicol resistance gene catQ.

In recent years mef genes, encoding efflux pumps responsible for M-type macrolide resistance, have been investigated extensively for streptococci. mef(I) is a recently described mef variant detected in particular isolates of Streptococcus pneumoniae instead of the more common mef(E) and mef(A). This study shows that mef(I) is located in a new composite genetic element, whose sequence was completely analyzed and the left and right junctions determined, demonstrating a unique genetic organization.

New Tn916-related elements causing erm(B)-mediated erythromycin resistance in tetracycline-susceptible pneumococci.

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.

Molecular characterization of pneumococci with efflux-mediated erythromycin resistance and identification of a novel mef gene subclass, mef(I).

The molecular genetics of macrolide resistance were analyzed in 49 clinical pneumococci (including an "atypical" bile-insoluble strain currently assigned to the new species Streptococcus pseudopneumoniae) with efflux-mediated erythromycin resistance (M phenotype). All test strains had the mef gene, identified as mef(A) in 30 isolates and mef(E) in 19 isolates (including the S. pseudopneumoniae strain) on the basis of PCR-restriction fragment length polymorphism analysis.

Analysis of the beta-lactamase plasmid of borderline methicillin-susceptible Staphylococcus aureus: focus on bla complex genes and cadmium resistance determinants cadD and cadX.

Borderline methicillin-susceptible Staphylococcus aureus strains are a rather homogeneous group, characterized by MICs of penicillinase-resistant penicillins (PRPs) at or just below the susceptibility breakpoint. Other features unique to this group include the presence of a pBW15-like beta-lactamase plasmid, the association with phage complex 94/96, and the production of a PRP-hydrolyzing beta-lactamase activity in addition to the classical penicillinase activity. The four HindIII fragments of pBORa53, a pBW15-like plasmid from the well-studied borderline S.

Synergistic potential of ceftazidime plus amikacin or levofloxacin against Pseudomonas aeruginosa as determined using a checkerboard and a disk diffusion technique.

The synergistic potential of ceftazidime plus amikacin or levofloxacin was assessed against 61 Pseudomonas aeruginosa isolates with variable susceptibility patterns to the 3 antibiotics. A checkerboard broth method and a disk diffusion method were used and compared. The latter, also easy to perform as a triple-disk assay, could be a helpful laboratory screening tool for drug synergism to drive possible combination treatments.

Molecular characterization of clinical Streptococcus pneumoniae isolates with reduced susceptibility to fluoroquinolones emerging in Italy.

Fifteen Streptococcus pneumoniae clinical isolates with reduced fluoroquinolone susceptibility (defined as a ciprofloxacin MIC of > or = 4 microg/ml), all collected in Italy in 2000-2003, were typed and subjected to extensive molecular characterization to define the contribution of drug target alterations and efflux mechanisms to their resistance. Serotyping and pulsed-field gel electrophoresis analysis indicated substantial genetic unrelatedness among the 15 isolates, suggesting that the new resistance traits arise in multiple indigenous strains rather than through clonal dissemination. Sequencing of the quinolone resistance-determining regions of gyrA, gyrB, parC, and parE demonstrated that point mutations producing single amino acid changes were more frequent in topoisomerase IV (parC mutations in 14 isolates and parE mutations in 13) than in DNA gyrase subunits (gyrA mutations in 7 isolates and no gyrB mutations observed).

Phenotypes and genotypes of erythromycin-resistant pneumococci in Italy.

Of 120 erythromycin-resistant pneumococci isolated in Italian hospitals, 39 (32.5%) were M-type isolates, carrying the mef gene alone. The mef gene was also detected, together with erm(AM), in one constitutively resistant isolate and in five isolates of the partially inducible phenotype.