Scientific Publications by FDA Staff

J Clin Microbiol 2017 Mar;55(3):931-41

Singleton ST382, an emerging clonal group of Listeria monocytogenes associated with three multistate outbreaks linked to contaminated stone fruit, caramel apples and leafy green salad.

Chen Y, Luo Y, Pettengill J, Timme R, Melka D, Doyle M, Jackson A, Parish M, Hammack TS, Allard M, Brown EW, Strain EA

Three multistate outbreaks between 2014 and 2016, involving case patients in and outside the United States, were linked to stone fruit, caramel apples and packaged leafy green salad contaminated with Listeria monocytogenes singleton ST382. Isolates from these outbreaks and other ST382 isolates not associated with these outbreaks were analyzed by whole genome sequencing (WGS) analysis. The primary difference among these three ST382 outbreak strains were single nucleotide polymorphisms (SNPs). WGS analysis using these SNPs differentiated ST382 from a clonal complex 1 outbreak strain co-contaminating the caramel apples. WGS clustered food, environmental and clinical isolates within each outbreak; and also differentiated among the three outbreak strains and epidemiologically unrelated ST382 isolates, which were indistinguishable by pulsed-field gel electrophoresis. ST382 appeared to be an emerging clone that started to diverge from its ancestor approximately 32 years ago from 2016. The number of nucleotide substitutions per genome (2.94 Mbp) per year for this clone was estimated to be 1.