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Pulsed-Field Gel Electrophoresis Analysis of Vibrio vulnificus Strains Isolated from Taiwan and the United States. Hin-chung Wong, 2004.Vibrio vulnificus is a marine bacterium that causes human wound infections and septicemia with a high mortality rate . V . vulnificus strains from different clinical and environmental sources or geographic regions have been successfully characterized by ribotyping and several other methods . Pulsed-field gel electrophoresis (PFGE) is a highly discriminative method, but previous studies suggested that it was not suitable for examining the correlation of V . vulnificus strains from different origins . We employed PFGE to determine its efficacy for characterizing V . vulnificus strains from different geographic regions, characterizing a total of 153 strains from clinical and environmental origins from the United States and Taiwan after SfiI or NotI digestion . V . vulnificus strains showed a high intraspecific diversity by PFGE after SfiI or NotI digestion, and about 12% of the strains could not be typed by the use of either of these enzymes . For PFGE with SfiI digestion, most of the clinical and environmental strains from the United States were grouped into cluster A, while the strains from Taiwan were grouped into other clusters . Clinical strains from the United States showed a higher level of genetic homogeneity than clinical strains from Taiwan, and environmental strains from both regions showed a similarly high level of heterogeneity . PFGE with NotI digestion was useful for studying the correlation of clinical strains from the United States and Taiwan, but it was not suitable for analyzing environmental strains . The results showed that PFGE with SfiI digestion may be used to characterize V . vulnificus strains from distant geographic regions, with NotI being a recommended alternative enzyme . Transposase-Dependent Formation of Circular IS256 Derivatives in Staphylococcus epidermidis and Staphylococcus aureus. Isabel Loessner, 2002.IS256 is a highly active insertion sequence (IS) element of multiresistant staphylococci and enterococci . Here we show that, in a Staphylococcus epidermidis clinical isolate, as well as in recombinant Staphylococcus aureus and Escherichia coli carrying a single IS256 insertion on a plasmid, IS256 excises as an extrachromosomal circular DNA molecule . First, circles were identified that contained a complete copy of IS256 . In this case, the sequence connecting the left and right ends of IS256 was derived from flanking DNA sequences of the parental genetic locus . Second, circle junctions were detected in which one end of IS256 was truncated . Nucleotide sequencing of circle junctions revealed that (i) either end of IS256 can attack the opposite terminus and (ii) the circle junctions vary significantly in size . Upon deletion of the IS256 open reading frame at the 3' end and site-directed mutageneses of the putative DDE motif, circular IS256 molecules were no longer detectable, which implicates the IS256-encoded transposase protein with the circularization of the element . Isolation of Tetracycline-Resistant Megasphaera elsdenii Strains with Novel Mosaic Gene Combinations of tet(O) and tet(W) from Swine. Thaddeus B. Stanton, 2003.
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