015 – 4 μg/ml), trimethoprim/sulfamethoxazole (0.12/2.38 – 4/76 μg/ml), cefoxitin (0.5 – 32 μg/ml), gentamicin (0.25 – 16 μg/ml), kanamycin (8 – 64 μg/ml), nalidixic acid (0.5 – 32 μg/ml), sulfisoxazole (15-256 μg/ml), streptomycin (32 – 64 μg/ml), tetracycline (4 – 32 μg/ml),

and ceftiofur (0.12 – 8 μg/ml). Salmonella isolates were recovered from frozen stock to Tryptone Soy DMXAA supplier Agar (TSA) and incubated at 37°C for 18-24 h; cell suspensions were prepared and adjusted to a 0.5 McFarland standard. Then, 10 μl of the suspension was added to 11 ml of Mueller-Hinton broth (Trek Diagnostics) and mixed; the NARMS panels were inoculated using the Sensititre® Autoinoculator (Trek Diagnostics) following the manufacturer’s instructions. The plates were sealed and incubated at 37°C for

18 h. After incubation, the plates were read using the Sensititre Autoreader (Trek Diagnostics) to record growth or no growth of the isolates in each of the wells. The minimum inhibitory concentration (MIC) was recorded for each isolate and compared to breakpoints that were defined by the CLSI. A breakpoint is defined as the minimum concentration of antimicrobial above which growth should not occur [34]. Breakpoints used in this study are indicated in the results section. CLSI specified positive control strain Escherichia coli ATCC 25922 was used to ensure the efficacy of the procedure for Salmonella. The isolates were recorded as resistant or sensitive for each antimicrobial according to breakpoints specified this website by CLSI [33]. PFGE analysis Pulsed Field Gel Electrophoresis GABA Receptor (PFGE) was performed as previously described [35] with slight modifications. Salmonella enterica serotype Braenderup H9812 (ATCC #BAA-664) was used as the molecular weight size standard. Restriction endonuclease digestion was carried out using 25 U

XbaI (Invitrogen, Carlsbad, CA) in a final volume of 100 μl at 37°C for 3 h. DNA macrorestriction fragments were resolved over 18 h on 1% SeaKem Gold Agarose (Cambrex, Rockland, ME) (in 0.5X TBE) using the Chef Mapper XA system (Bio-Rad, Hercules, CA) auto algorithm function for a low molecular weight of 30 kb and a high molecular weight of 600 kb. Gels were stained in 1 μg ethidium bromide ml-1 in reagent grade water for 30 min, with washes as needed and the restriction patterns visualized by UV transillumination using an Alpha Innotech Imager (Alpha Innotech, Santa Clara, CA). Macrorestriction patterns were compared using the BioNumerics Fingerprinting software (Version 6.5, Applied Math, Austin, TX). The similarity index of the isolates was calculated using the Dice correlation coefficient option of the software with a position tolerance of 1% and an optimization of 0.5%. The unweighted-pair group method using average linkages (UPGMA) was used to construct a dendrogram.