Pulsed-Field Gel Electrophoresis (PFGE)

Pulsed-field gel electrophoresis of the strains was processed in accordance with the PulseNet International protocol¹. Slices of L. monocytogenes agarose plugs were digested using 50 U of AscI and ApaI (Takara, Dalian, China) per slice for 3 h at 37°C; electrophoresis was performed using a CHEF-DRIII system (Bio-Rad Laboratories, Hercules, CA, United States); electrophoresis was conducted with a switch time of 4–40 s for 19 h; and images were captured using a Gel Doc 2000 system (Bio-Rad) then converted to TIFF files. Salmonella enterica serovar Braenderup strain H9812 restricted with XbaI was used for molecular weight determinations in all PFGE gels. The TIFF files were analyzed using BioNumerics software (version 7.6 Applied Maths, Kortrijk, Belgium). Clustering was performed using the unweighted pair group method with arithmetic mean (UPGMA).