Vibrio parahaemolyticus (Vp) is an important foodborne pathogen worldwide and has been one leading cause of seafood-associated human gastroenteritis in the United States. However, knowledge gap still exists about the fitness and survival mechanisms of Vp in pre-harvest environment.
Two pathogenic ATCC strains of VP43996 (tdh+) and VP17802 (trh+) were used as the model organisms. Overnight fresh and washed cultures were inoculated into autoclaved natural seawater and stored at 10 °C for 10 days and 30 °C for 5 days (representing the average seawater temperatures in winter and summer months). The surviving Vp was determined by plating inoculated seawater onto thiosulfate-citrate-bile salts-sucrose agar (TCBS). Total RNA was extracted from the artifically-inoculated seawater 2 hours after inoculation and on Day 5 for samples stored at 10 and 30 °C by using the Qiagen RNAeasy mini kits. cDNA library was prepared by using the Qiagen QuantiTect Reverse Transcription Kit and sequenced with the Illumina Hiseq platform to produce 2 x 50 bp pair end short reads. Transcriptomics analysis was conducted to profile the transcriptome of Vp at different harvesting water temperatures.
The survival of Vp in artificially-inoculated seawater at two storage temperatures are illustrated in Figure 1. At 10 °C, the trh+ strain survived with greater numbers than the tdh+ strain. At 30 °C, the viable counts of both Vp strains reached plateau after 24 hours and remained at ~6.8 Log CFU/ml for the rest of the storage time. Compared with the strains stored at 30 °C, the Gene Set Enrichment Analysis based on the Kyoto Encyclopedia of Genes and Genomes (GSEA-KEGG) in Figure 2 provides biological insights of Vp persisted in seawater at 10 °C. It was found that both the histidine metabolism and biofilm formation metabolism pathways were significantly downregulated for both Vp strains at 10 °C.