title: Changing plasmid types responsible for extended spectrum cephalosporin resistance inEscherichia coliO157:H7 in the United States, 1996-2009.
abstract: Escherichia coliO157 is a major cause of foodborne illness. Plasmids are genetic elements that mobilize antimicrobial resistance determinants includingblaCMYβ-lactamases that confer resistance to extended-spectrum cephalosporins (ESC). ESCs are important for treating a variety of infections. IncA/C plasmids are found among diverse sources, including cattle, the principal source ofE. coliO157 infections in humans. IncI1 plasmids are common amongE. coliandSalmonellafrom poultry and other avian sources. To broaden our understanding of reservoirs ofblaCMY, we determined the types of plasmids carryingblaCMYamongE. coliO157. From 1996 to 2009, 3742E. coliO157 isolates were tested. Eleven (0.29%) were ceftriaxone resistant and had ablaCMY-2-containing plasmid. All four isolates submitted before 2001 and a single 2001 isolate hadblaCMYencoded on IncA/C plasmids, while all five isolates submitted after 2001 and a single 2001 isolate hadblaCMYcarried on IncI1 plasmids. The IncI1 plasmids were ST2, ST20, and ST23. We conclude that cephalosporin resistance amongE. coliO157:H7 is due to plasmid-encodedblaCMYgenes and that plasmid types appear to have shifted from IncA/C to IncI1. This shift suggests either a change in plasmid type among animal reservoirs or that the organism has expanded into avian reservoirs. More analysis of human, retail meat, and food animal isolates is necessary to broaden our understanding of the antimicrobial resistance determinants of ESC resistance amongE. coliO157.
authors.affiliation: CDC, Division of Foodborne, Waterborne and Environmental Diseases ; IHRC, Inc.
authors.forename: J P
authors.initials: JP
authors.lastname: Folster
authors.affiliation: CDC, Division of Foodborne, Waterborne and Environmental Diseases ; IHRC, Inc.
authors.forename: G
authors.initials: G
authors.lastname: Pecic
authors.affiliation: CDC, Division of Foodborne, Waterborne and Environmental Diseases.
authors.forename: S
authors.initials: S
authors.lastname: Stroika
authors.affiliation: CDC, Division of Foodborne, Waterborne and Environmental Diseases.
authors.forename: R
authors.initials: R
authors.lastname: Rickert
authors.affiliation: CDC, Division of Foodborne, Waterborne and Environmental Diseases.
authors.forename: J
authors.initials: J
authors.lastname: Whichard
keywords: Antimicrobial resistance; Escherichia coli O157:H7; cephalosporin resistance; resistance plasmid