The internal review boards and ethics committees of all collaborating hospitals in the surveillance network approved the protocol, and

written informed consent was collected from the guardians of all participants to obtain fecal and/or blood samples, and use the clinical and microbiologic information for scientific studies [57]. We did not use a systematic randomization method for selecting strains for this study. Using a chart with a list of each isolate by city of origin, strains were manually selected by including at least one strain from animals, meat or humans from a total of 61 cities. The sample included 38 isolates from Yucatán, 22 from Michoacán, 32 from San Luis Potosí and 22 from Sonora. Sixty-two isolates GS-1101 cell line were from human samples (45 with diarrhea, 11 asymptomatic and 6 with systemic infection), and 52 from food-animals (18 from pork, 14 from beef, 6 from chicken meat, 10 from swine intestine, and 4

from cattle intestine). Isolates collected during 2000 and 2001 were only available from Yucatán and San Luis Potosí. Isolates 3-deazaneplanocin A collected from 2002 to 2005 were available for all four states (Table 1 and Figure 3). Isolates biochemically confirmed to be Salmonella were serotyped according to the Kauffmann-White scheme with commercial antisera, as described elsewhere [73]. All isolates were tested with the disk diffusion method [74] for susceptibility to ampicillin, chloramphenicol, sulfisoxazole, streptomycin, Avelestat (AZD9668) tetracycline, gentamicin, kanamycin, nalidixic acid, trimethoprim-sulfamethoxazole, ciprofloxacin and ceftriaxone. The minimum inhibitory concentrations (MICs) for ciprofloxacin and ceftriaxone were determined by agar dilution according to Clinical and Laboratory Standards Institute guidelines [75]. For the interpretation of MIC results for ciprofloxacin, high-level resistance was defined as a MIC value ≥ 2 μg/mL; low-level resistance was

defined as a MIC value ≥ 0.25 μg/mL and ≥ 1 μg/mL. MLST analysis Genomic DNA was extracted using the AquaPure Genomic DNA Kits (Bio-Rad Laboratories, Hercules, California, USA). PCR amplifications were performed with Taq DNA Polymerase (Invitrogen, Brazil), products were purified with a PCR purification kit from Qiagen (Valencia, California, USA) according to the manufacturer’s recommendation, and submitted for sequencing at Macrogen (Seoul, South Korea). MLST was based on the partial sequences (~450 bp) of the following seven housekeeping genes: aroC, dnaN, hemD, hisD, purE, sucA and thrA, according to the Salmonella MLST database [45]. The primers for PCR and sequencing were previously described by Kidgell et al. (2002) [53].