Salmonella Isolates Genome Sequencing

All the bacterial strains used in this study were previously reported [1 (link)]. Briefly, the isolates were collected from a four-state integrated surveillance system for Salmonella in Mexico [10 (link)]. The geographic locations of these states range from the Northwestern (Sonora) to the Southeastern (Yucatán) part of Mexico, located about 2,000 km apart, and the Central states of Michoacán and San Luis Potosí (about 450 km far apart). For genome sequencing and PCR procedures, DNA was extracted from liquid cultures by a modification of the salt extraction method [11 (link)] described in [12 (link)]. To analyze the plasmid content for selected isolates, a modified protocol of the alkaline lysis procedure [13 (link)] was used as described previously [12 (link)]. The products were separated in 0.7% agarose gels in 1X TBE buffer at 100 volts for 5 hours, stained in 1% ethidium bromide and photographed. The plasmid profile gels were transferred to positively charged membranes (Amersham Hybond^TM -N⁺) and hybridized with ³²P-radioactively-labelled probes by standard methods [14 ]. Hybridizations were carried out at 65°C.