CTX-M-65 Extended-Spectrum β-Lactamase-Producing Salmonella enterica Serotype Infantis, United States1

Abstract

Extended-spectrum β-lactamases (ESBLs) confer resistance to clinically important third-generation cephalosporins, which are often used to treat invasive salmonellosis. In the United States, ESBLs are rarely found in Salmonella. However, in 2014, the US Food and Drug Administration found bla_CTX-M-65 ESBL-producing Salmonella enterica serotype Infantis in retail chicken meat. The isolate had a rare pulsed-field gel electrophoresis pattern. To clarify the sources and potential effects on human health, we examined isolates with this pattern obtained from human surveillance and associated metadata. Using broth microdilution for antimicrobial susceptibility testing and whole-genome sequencing, we characterized the isolates. Of 34 isolates, 29 carried the bla_CTX-M-65 gene with <9 additional resistance genes on 1 plasmid. Of 19 patients with travel information available, 12 (63%) reported recent travel to South America. Genetically, isolates from travelers, nontravelers, and retail chicken meat were similar. Expanded surveillance is needed to determine domestic sources and potentially prevent spread of this ESBL-containing plasmid.

Keywords: CTX-M-65; ESBL; Salmonella; Salmonella enterica; United States; antibacterial agents; antimicrobial resistance; bacteria; beta-lactamases; drug resistance; extended-spectrum β-lactamase–producing; poultry; serotype Infantis; travel; treatment failure.

Figure 1

Total of 312 Salmonella enterica serotype Infantis isolates from humans with pattern JFXX01.0787 as a percentage of all Salmonella Infantis isolates by year, United States, 2012–2017. Source: PulseNet (https://www.cdc.gov/pulsenet/index.html).

Figure 2

High-quality single-nucleotide polymorphism–based phylogenetic tree of clinical and retail meat isolates of Salmonella enterica serotype Infantis with pulsed-field gel electrophoresis pattern JFXX01.0787 collected in the United States and submitted to the National Antimicrobial Resistance Monitoring System for whole-genome sequencing. Tree tips are labeled with National Center for Biotechnology Information accession numbers (sequence read archive run identification numbers); shading indicates patients’ international travel history for clinical isolates (black, recent international travel; gray, no recent international travel; white, travel data missing). Black circles indicate isolates that are missing the bla_CTX-M-65 gene. Isolates in top clade differed by 2–47 high-quality single-nucleotide polymorphisms. Numbers displayed on nodes are bootstrap support values, an indication of the reliability of the tree. Only bootstrap values >80 are displayed. More information on patient and isolate characteristics are provided in Tables 1 and 2. Scale bar indicates nucleotide substitutions per site.