Prevalence of bla CTX-M Genes in Gram-Negative Bloodstream Isolates across 66 Hospitals in the United States

Understanding bacterial species at greatest risk for harboring bla CTX-M genes is necessary to guide antibiotic treatment. We identified the species-specific prevalence of bla CTX-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 bla CTX-M genes, it detects major carbapenemase gene families. A total of 4,209 Gram-negative blood cultures were included. bla CTX-M genes were identified in 462 (11%) specimens. The species-specific prevalence of bla CTX-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%). bla CTX-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: bla KPC (59%), bla VIM (16%), bla OXA (10%), bla NDM (8%), and bla IMP (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 bla CTX-M genes. bla CTX-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.