Prevalence of blaCTX-M genes in gram-negative bloodstream isolates across 66 hospitals in the United States

Pranita D. Tamma, Tiffeny T. Smith, Ayomikun Adebayo, Sara M. Karaba, Emily Jacobs, Teresa Wakefield, Kelly Nguyen, Natalie N. Whitfield, Patricia J. Simner

Research output: Contribution to journalArticlepeer-review


Understanding bacterial species at greatest risk for harboring blaCTX-M genes is necessary to guide antibiotic treatment. We identified the species-specific prevalence of blaCTX-M genes in Gram-negative clinical isolates from the United States. Twenty-four microbiology laboratories representing 66 hospitals using the GenMark Dx ePlex blood culture identification Gram-negative (BCID-GN) panel extracted blood culture results from April 2019 to July 2020. The BCID-GN panel includes 21 Gram-negative targets. Along with identifying blaCTX-M genes, it detects major carbapenemase gene families. A total of 4,209 Gram-negative blood cultures were included. blaCTX-M genes were identified in 462 (11%) specimens. The species-specific prevalence of blaCTX-M genes was as follows: Escherichia coli (16%), Klebsiella pneumoniae (14%), Klebsiella oxytoca (6%), Salmonella spp. (6%), Acinetobacter baumannii (5%), Enterobacter species (3%), Proteus mirabilis (2%), Serratia marcescens (0.6%), and Pseudomonas aeruginosa (0.5%). blaCTX-M prevalence was 26%, 24%, and 22% among participating hospitals in the District of Columbia, New York, and Florida, respectively. Carbapenemase genes were identified in 61 (2%) organisms with the following distribution: blaKPC (59%), blaVIM (16%), blaOXA (10%), blaNDM (8%), and blaIMP (7%). The species-specific prevalence of carbapenemase genes was as follows: A. baumannii (5%), K. pneumoniae (3%), P. mirabilis (3%), Enterobacter species (3%), Citrobacter spp. (3%), P. aeruginosa (2%), E. coli (,1%), K. oxytoca (,1%), and S. marcescens (,1%). Approximately 11% of Gram-negative organisms in our US cohort contain blaCTX-M genes. blaCTX-M genes remain uncommon in organisms beyond E. coli, K. pneumoniae, and K. oxytoca. Future molecular diagnostic panels would benefit from the inclusion of plasmid-mediated ampC and SHV and TEM extended-spectrum beta-lactamase (ESBL) targets.

Original languageEnglish (US)
Article numbere00127-21
JournalJournal of clinical microbiology
Issue number6
StatePublished - Jun 2021


  • AMR
  • Antimicrobial resistance
  • Ceftriaxone
  • ESBLs

ASJC Scopus subject areas

  • Microbiology (medical)


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