Conjugations were performed using both the Salmonella isolates and their respective E. coli transformants. Ceftriaxone (2 μg/ml) and chloramphenicol (15 μg/ml) were used to select for the transfer of CMY+ and CMY- plasmids, respectively. Transfer efficiencies were calculated as the number of transconjugants per donor. Acknowledgements This work was partially funded by research grants from CONACyT/Mexico
(No.82383 and No. 60227) and DGAPA/UNAM (No. 216310 and 205107) to EC and Ricardo Oropeza; by a Ph.D. fellowship from CONACyT (No. 214945) to MW; and by a postdoctoral fellowship to CS from CONACyT (No. 60796). We are grateful to all the people that kindly supplied reference strains: E. coli V157 was provided by Francis L. Macrina, E. coli AR060302 was provided by Douglas R. Call, Newport SN11 was provided by Toni L. Poole and Dayna Harhay, and E. coli E2348/69 was provided by Alejandro Huerta. selleck screening library We appreciate the technical assistance of Elvira Villa; the administrative support of Amapola Blanco and
Rosalva González; and the primer synthesis and sequencing service given by Eugenio López, Santiago Becerra, Paul Gaytán and Jorge Yañez at the Instituto de Biotecnología, UNAM. Rafael Díaz (CCG, UNAM) and Cindy Dierikx (Central Veterinary Institute, the Netherlands) helped us with the S1 PFGE protocol. Electronic supplementary material Additional file 1: Table S1. Primers used in this study. (DOC 113 KB) Additional file 2: Table S2. learn more Isolates sequenced and GenBank accession numbers. (DOC 36 KB) References 1. Levin BR, Bergstrom CT: Bacteria are different: observations, interpretations, speculations, and Compound C opinions about the DOK2 mechanisms of adaptive evolution in prokaryotes. Proc Natl Acad Sci USA 2000, 97: 6981–6985.PubMedCrossRef 2. Heuer H, Abdo Z, Smalla K: Patchy distribution of flexible genetic elements in bacterial populations mediates robustness to environmental uncertainty. FEMS Microbiol Ecol 2008,
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