DYNAMICS AND INTERACTIONS OF EMERGENT AND INVASIVE PATHOGENIC LINEAGES OF VIBRIO PARAHAEMOLYTICUS IN THE NORTHEASTERN U.S.

V. parahaemolyticus the leading causes of seafood-borne bacterial infections in the United States (US), can live freely in brackish water or associated with shellfish. V. parahaemolyticus is genetically diverse. The majority of strains are harmless, whereas the minority are human pathogens. Outbreaks caused by V. parahaemolyticus used to be extremely rare in cooler regions like the Northeast US, but illnesses have risen dramatically in the past decade. The increased cases not only cause revenue loss for shellfish industries, but also impose public health risks. Little was known about the causes of these unprecedented increase in infections in the Northeast US. The mechanisms of the emergence of the pathogens were also uncertain. This study identifies the major lineages responsible for the infections in the Northeast US, and elucidates the evolution and emergence of the pathogens. It also develops effective and targeted detection methods. The Pacific-native ST36 lineage, which has invaded and now resides in this region, and major endemic lineages, chiefly ST631, caused the increase in illnesses. ST631 has diverged into two distinct clades and independently acquired different virulence traits that resulted in their variable clinical prevalence: ST631 clade II is the most prevalent endemic lineage along the Atlantic Coast. Further analysis suggested that the laterally transferred and exchanged genetic elements in isolates from the ST631 clade II originated from Pacific lineages, possibly ST36. Therefore, the interactions between invasive and endemic strains shaped the evolution and emergence of the endemic lineages. Whole genomic comparisons also allowed the development of detection tools to specifically target a majority of the pathogens in the Northeast. This should aid in more precise monitoring of the abundance of pathogenic lineages to potentially predict outbreaks, substantially reduce public health burden. Overall, this study built the framework for understanding how invasive lineages can shape local population structure change. It also demonstrated how two lineages that originated from the same ancestor could evolve independently to become pathogens that vary in clinical prevalence, which suggests the predisposition of the genome contents may have played a role in acquiring, regulating and maintaining foreign DNA