P3-228 Seasonality, Diversity and Indicators of Salmonella Contamination of Environmental Surface Waters of the Virginia Eastern Shore

Wednesday, July 12, 2017
Exhibit Hall (Tampa Convention Center)
Christina M. Ferreira , U.S. Food and Drug Administration , College Park , MD
Elizabeth Reed , U.S. Food and Drug Administration , College Park , MD
Amir Mokhtari , U.S. Food and Drug Administration , College Park , MD
Yan Luo , U.S. Food and Drug Administration , College Park , MD
Jie Zheng , U.S. Food and Drug Administration , College Park , MD
Rebecca L. Bell , U.S. Food and Drug Administration , College Park , MD
Introduction: Environmental surveys along the Virginia Eastern Shore (VES) have identified Salmonella as a persistent inhabitant of environmental surface waters.  Since surface waters may contact fresh produce, via irrigation or field flooding, good indicators for Salmonellaare needed for easier prediction of possible contamination. 

Purpose: This study examined potential correlations between Salmonella concentration in surface waters along the VES and other biological and/or physical indicators; to characterize seasonality in Salmonellalevels recovered during a one-year sampling period; and to examine serotype diversity.

Methods: Water and sediment samples were collected from six surface water sites in VES and two in West Virginia for a one-year period (October 2014 - September 2015).  Physical parameters of the water were evaluated in situ.  Water samples were enumerated for Salmonella, using a MPN method, and coliforms/fecal coliforms using the IDEXX Colilert® system.  Sediment samples were tested for the presence of Salmonella.  MPN estimates were compared to the physical water parameters on a statistical basis.  Salmonellaisolates were sequenced, and serotypes determined by molecular serotyping or genome sequence.  Genomic comparisons were conducted using the FDA/CFSAN SNP pipeline.   

Results: Preliminary results showed moderate correlations between log-transformed values (log10 MPN/100ml) and water temperature (°C) (0.51 and 0.53, Salmonella and fecal coliforms, respectively) as well as conductivity (0.38 and 0.37, Salmonella and fecal coliforms, respectively). Also a moderate correlation between log-transformed values of Salmonellaand fecal coliforms was detected (correlation coefficient of 0.55).  Over 500 isolates, representing thirty-two unique serovars were obtained.  The number and diversity varied with site and month.  Genomic analysis revealed over 430,000 SNPs between these diverse strains.  The resultant tree sorted the strains by serovar with no polyphyly observed.

Significance: The data gathered in this study will aid in the development of risk assessment models and new preventative controls strategies designed to reduce or eliminate preharvest contamination of fresh produce.