Characterization of extended-spectrum cephalosporin-resistant Salmonella enterica serovar Heidelberg isolated from humans in the United States.
During the past decade, extended-spectrum cephalosporin resistance has increased among human isolates of Salmonella enterica serovar Heidelberg, the fourth most common serotype in the United States. We therefore characterized 54 Heidelberg isolates with decreased susceptibility (minimum inhibitory concentrations >or=2 mg/L) to ceftriaxone or ceftiofur; 49 (90.7%) contained the CMY-type beta-lactamase (bla(CMY)) gene. The 49 bla(CMY)-positive human Heidelberg isolates demonstrated a high degree of relatedness; 4 clusters (25 isolates total) had indistinguishable XbaI and BlnI patterns by pulsed-field gel electrophoresis and were indistinguishable from 42 retail meat Heidelberg isolates. Further characterization of 15 of these isolates demonstrated that all of the bla genes were bla(CMY-2) and plasmid-encoded, and most (11/15) of the plasmids were approximately 100 kb in size and belong to the incompatibility group I1 (IncI1). All five IncI1 plasmids tested by plasmid multilocus sequence typing analysis were ST12. This report suggests that extended-spectrum cephalosporin resistance among human Heidelberg isolates is mediated by the spread of a common IncI1 bla(CMY-2) plasmid, which may have a preference for a particular genetic background.
Division of Foodborne, Bacterial, and Mycotic Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia 30329, USA.
Jason P
JP
Folster
Gary
G
Pecic
Shanna
S
Bolcen
Lisa
L
Theobald
Kelley
K
Hise
Alessandra
A
Carattoli
Shaohua
S
Zhao
Patrick F
PF
McDermott
Jean M
JM
Whichard
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001483:Base Sequence; D002511:Cephalosporins / Q000494:pharmacology*; D016000:Cluster Analysis; D004269:DNA, Bacterial / Q000032:analysis; D004305:Dose-Response Relationship, Drug; D024881:Drug Resistance, Bacterial / Q000235:genetics; D005516:Food Microbiology; D006801:Humans; D008460:Meat / Q000382:microbiology*; D008826:Microbial Sensitivity Tests; D010957:Plasmids; D016133:Polymerase Chain Reaction; D012478:Salmonella Food Poisoning / Q000382:microbiology; D019779:Salmonella enterica / Q000145:classification / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D012703:Serotyping; D014481:United States; D001618:beta-Lactamases / Q000235:genetics
D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D004269:DNA, Bacterial; D001618:beta-Lactamases