Purpose: DCLS conducts laboratory testing of foodborne pathogens in support of local surveillance and outbreak investigations conducted by the Virginia Department of Health (VDH) and VDACS. DCLS also performs molecular subtyping by pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS) of these pathogens in support of the CDC PulseNet and FDA GenomeTrakr Networks.
Methods: Sprout samples and environmental swab composites submitted to DCLS were VIDAS LIS-screened for Listeria spp. Isolation of L. monocytogenes from screen-positive samples was performed per the FDA Bacterial Analytical Manual. L. monocytogenes isolates from all sources were further characterized by PFGE and WGS.
Results: L. monocytogenes from soybean sprouts shared the same PFGE DNA fingerprint pattern type as a listeriosis patient isolate tested by DCLS in April 2015. Both isolates were determined to be highly genetically related by WGS. Comparison of the WGS results to other clinical isolates identified two additional highly genetically related isolates from 2014. Environmental sampling at the processor identified environmental contamination with L. monocytogenes of the same PFGE-type, also highly genetically related by WGS, suggesting that the pathogen was a resident contaminant.
Significance: Through the VA Rapid Response Team, neighboring states receiving the product were notified and a recall of contaminated sprouts was released in May 2015. Subsequent testing of sprouts from the firm identified additional L. monocytogenes-contaminated product that was again highly genetically related to earlier product, environmental, and clinical isolates by WGS. Regulatory action based on these findings resulted in two additional recalls before the firm permanently closed in November 2015.