First Clinical Case of In Vivo Acquisition of DHA-1 Plasmid-Mediated AmpC in a Salmonella enterica subsp. enterica Isolate.

A pan-susceptible Salmonella enterica serovar Worthington isolate was detected in the stool of a man returning from Sri Lanka. Under ceftriaxone treatment, a third-generation cephalosporin (3GC)-resistant Salmonella Worthington was isolated after 8 days. Molecular analyses indicated that the two isolates were identical. However, the latter strain acquired a bla DHA-1-carrying IncFII plasmid probably from a Citrobacter amalonaticus isolate colonizing the gut. This is the first report of in vivo acquisition of plasmid-mediated resistance to 3GCs in S. enterica.