title: Instability of Escherichia coli R-factors in Salmonella enterica serovar Typhi involves formation of recombinant composite plasmid structures.
abstract: In spite of a well-documented ability of Samonella enterica Typhi strains to receive R factors from Escherichia coli and other enterobacteria, epidemiological data show that Typhi is a rather poor host of antibiotic-resistance genes and in fact, of plasmids, suggesting that most of the plasmids naturally acquired by Typhi strains become unstable and eventually segregate. We have previously reported evidence that each of three plasmids conjugatively transferred to S. enterica Typhi experienced deletion-mediated loss of a resistance determinant before plasmid segregation occurred. We now report that in Typhi strains containing these unstable plasmids a superhelical DNA species of lower mobility is detected, probably representing plasmid dimer structures. Plasmid deletion is a RecA-dependent process since it is not detected in derivatives of a recA1 S. enterica Typhi strain containing the corresponding plasmids, and in such strains we were unable to detect either the low-mobility species. We propose that the deletable segments contain key information for plasmid stability in S. enterica Typhi, possibly a multimer resolution system.
authors.affiliation: Departamento de Bioquímica, Facultad de Medicina, Universidad Autónoma del Estado de México, Paseo Tollocan esquina Jesús Carranza, CP 50180, Toluca, Estado de México, Mexico. menmeau777@hotmail.com
authors.forename: Aurelio
authors.initials: A
authors.lastname: Mendoza-Medellín
authors.forename: Rafael
authors.initials: R
authors.lastname: Camacho-Carranza
authors.forename: Everardo
authors.initials: E
authors.lastname: Curiel-Quesada
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D004352:Drug Resistance, Microbial / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics*; D010957:Plasmids / Q000235:genetics; D011815:R Factors / Q000235:genetics*; D011995:Recombination, Genetic; D012485:Salmonella typhi / Q000187:drug effects / Q000235:genetics*
chemical_list: D000900:Anti-Bacterial Agents