Puskar Siwakoti

Puskar Siwakoti

University of New Hampshire

Medical Microbiology


Mentor: Dr. Cheryl Whistler, Department of Molecular, Cellular, and Biomedical Sciences

Investigation of virulence of emergent vibrio parahaemolyticus

Vibrio parahaemolyticus is the leading causes of seafood-borne bacterial gastroenteritis in the US, but an overall lack of understanding of virulence is a major obstacle for predicting and preventing disease. Several outbreaks in 2012 and 2013 in New England were apparently caused by an invasive sequence type 36 (ST36) strain that appears more virulent than endemic strains. Unlike many other bacteria, V. parahaemolyticus represses virulence under high cell densities by using quorum sensing, a form of community communication allowing cells to coordinate gene expression. It has been noted that many pathogenic strains of V. parahaemolyticus historically used in research are quorum blind leading to increased virulence, suggesting an intriguing hypothesis that altered quorum sensing promotes evolution of more virulent strains. The proposed study 1) investigated the extent clinical strains are quorum blind compared to harmless environmental strains, 2) evaluated whether altered quorum sensing is likely the result of laboratory handing rather than a natural avenue to enhance virulence, and 3) determined whether highly-virulent ST36 strains are quorum blind. Recently isolated and historic clinical strains, as well as environmental strains were evaluated for their quorum sensing characteristics both phenotypically and genetically. Clinical strains were more often quorum blind compared to the environmental strains; however, data (both phenotype and genotype) do not suggest that historical clinical were more often quorum blind compared to other clinical strains, indicating this is a potential mechanism for evolution of virulence and not artifact of handling. Both recent and historical ST36 strains exhibited normal quorum sensing, indicating enhance virulence is not likely due to quorum blindness.  This study improves our understanding of the evolution of this pathogen’s virulence, which may help in minimizing human diseases caused by this and other similar pathogens.


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