Characterization of Resistance Genes and Plasmids from Outbreaks and Illness Clusters Caused by Salmonella Resistant to Ceftriaxone in the United States, 2011-2012

Microb Drug Resist. 2017 Mar;23(2):188-193. doi: 10.1089/mdr.2016.0080. Epub 2016 Nov 9.


Salmonella is an important cause of foodborne illness; however, quickly identifying the source of these infections can be difficult, and source identification is a crucial step in preventing additional illnesses. Although most infections are self-limited, invasive salmonellosis may require antimicrobial treatment. Ceftriaxone, an extended-spectrum cephalosporin, is commonly used for treatment of salmonellosis. Previous studies have identified a correlation between the food animal/retail meat source of ceftriaxone-resistant Salmonella and the type of resistance gene and plasmid it carries. In this study, we examined seven outbreaks of ceftriaxone-resistant Salmonella infections, caused by serotypes Typhimurium, Newport, Heidelberg, and Infantis. All isolates were positive for a plasmid-encoded blaCMY gene. Plasmid incompatibility typing identified five IncI1 and two IncA/C plasmids. Both outbreaks containing blaCMY-IncA/C plasmids were linked to consumption of cattle products. Three of five outbreaks with blaCMY-IncI1 (ST12) plasmids were linked to a poultry source. The remaining IncI1 outbreaks were associated with ground beef (ST20) and tomatoes (ST12). In addition, we examined isolates from five unsolved clusters of ceftriaxone-resistant Salmonella infections and used our plasmid-encoded gene findings to predict the source. Overall, we identified a likely association between the source of ceftriaxone-resistant Salmonella outbreaks and the type of resistance gene/plasmid it carries.

Keywords: Salmonella; antimicrobial; plasmid; resistance.

MeSH terms

  • Animals
  • Anti-Bacterial Agents / pharmacology*
  • Ceftriaxone / pharmacology*
  • Cephalosporins / pharmacology
  • DNA, Bacterial / genetics
  • Disease Outbreaks
  • Drug Resistance, Bacterial / genetics*
  • Foodborne Diseases / microbiology
  • Meat / microbiology
  • Plasmids / genetics*
  • Salmonella / drug effects*
  • Salmonella / genetics*
  • Salmonella Infections / drug therapy
  • Salmonella Infections / microbiology
  • United States


  • Anti-Bacterial Agents
  • Cephalosporins
  • DNA, Bacterial
  • Ceftriaxone