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<jats:title>ABSTRACT</jats:title> <jats:p>The first outbreak of multidrug-resistant (MDR) typhoid fever in Vietnam was in 1993, and by 1995 nearly 90% of cases were MDR. Plasmid HCM1, sequenced in full, is an incHI1 plasmid from <jats:italic>Salmonella enterica</jats:italic> serovar Typhi strain CT18, isolated in Vietnam in 1993. Restriction analysis shows that pHCM1 shares a restriction fragment length polymorphism (RFLP) pattern with plasmids isolated from the first outbreak and 10 of 17 MDR plasmids isolated from sporadic cases occurring at the same time in Vietnam. A core region of pHCM1 has significant DNA sequence similarity to plasmid R27, isolated in 1961 from <jats:italic>S. enterica</jats:italic> in the United Kingdom. There are five regions of DNA in pHCM1 which are not present in R27. Two of these are putative acquisition regions; the largest is 34.955 kbp in length and includes sequences of several antibiotic resistance genes and several insertion sequences. The borders of this region are defined by two identical IS<jats:italic>10</jats:italic> left elements, associated with an inversion of DNA or with a truncated Tn<jats:italic>10</jats:italic> element. The second, smaller region is 14.751 kbp and carries a trimethoprim resistance gene <jats:italic>dfr14A</jats:italic> cassette associated with a class 1 integrase. In 1993 to 1994, restriction analysis revealed some variations in the structures of <jats:italic>Salmonella</jats:italic> serovar Typhi MDR plasmids which were mapped to the two putative acquisition regions and three smaller variable regions. In 1996 a single RFLP type, RFLP7, was found to carry the <jats:italic>dfrA7</jats:italic> and <jats:italic>sul</jats:italic>-<jats:italic>1</jats:italic> genes, which were not present on R27 or pHCM1. This plasmid type appears to have a selective advantage over other plasmids with the same resistance phenotype.</jats:p>

Original publication





Antimicrobial Agents and Chemotherapy


American Society for Microbiology

Publication Date





2732 - 2739