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T2-12 Molecular Epidemiology of an Emerging Strain of Salmonella enterica serotype Infantis in the United States

Monday, July 10, 2017: 11:45 AM
Room 16 (Tampa Convention Center)
Jessica Chen , IHRC Inc. , Atlanta , GA
Allison Brown , Centers for Disease Control and Prevention , Atlanta , GA
Lee Katz , Centers for Disease Control and Prevention , Atlanta , GA
Davina Campbell , Centers for Disease Control and Prevention , Atlanta , GA
Heather Tate , U.S. Food and Drug Administration - Center for Veterinary Medicine , Laurel , MD
Jason Folster , Centers for Disease Control and Prevention , Atlanta , GA
Audio File Recorded Presentation
Introduction: In July, 2015, FDA notified CDC of a CTX-M-65 producing isolate of Salmonella Infantis with a rare pulsed field gel electrophoresis pattern, JFXX01.0787, recovered from retail chicken meat. CTX-M confers resistance to 3rd generation cephalosporins including ceftriaxone, an important antibiotic used to treat invasive salmonellosis.

Purpose: The purpose of this study was to characterize a resistant strain of Salmonella Infantis by whole genome sequencing (WGS) and to better understand associated risk factors.

Methods: CDC performed WGS on 34 human clinical isolates of Salmonella Infantis pattern JFXX01.0787 and examined associated epidemiological data. Resistance determinants were identified using ResFinder. A high quality SNP (hqSNP) phylogeny was generated using Lyve-SET and a molecular clock analysis was implemented in BEAST.

Results: Epidemiological data showed an association with travel to South America in some clinical cases. WGS revealed that 29 of the 34 isolates possessed blaCTX-M-65. The hqSNP analysis revealed that the majority of isolates formed a well-supported clade that also included the retail chicken isolate. Isolates in this clade differed by no more than 48 hqSNPs and travel and nontravel isolates did not cluster separately. These Salmonella Infantis isolates diverged from a common ancestor around February, 2006 (95% HPD Interval: 8/1/2004 to 2/23/2011), prior to the first isolation of pattern JFXX01.0787 in 2012. Examination of the resulting maximum-clade credibility tree, with tree tips labeled with travel status, revealed that isolates from patients with a history of travel were recovered consistently over the study period (2012 to 2015), whereas domestic cases with no history of travel first emerged in 2014.

Significance: Epidemiological data indicated that travel is a risk factor for exposure to this strain. Further, the close genetic relationship of a domestic chicken isolate with several clinical isolates in this study suggested that chicken may play a role in transmission of this strain.

Back to: Technical Session 2 - Molecular Analytics, Genomics, and Microbiome
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