Date of Award

Summer 7-14-2020

Degree Type


Degree Name

Master of Science in Integrative Biology (MSIB)



Committee Chair/First Advisor

Tsai-Tien Tseng Ph.D.

Major Professor

Donald J. McGarey Ph.D.

Second Committee Member

Martin L. Hudson Ph.D.


Aeromonads are bacteria found globally in fresh and brackish waters, with some species causing water-borne diseases vertebrate hosts such as diarrhea and wound-infections in humans and motile Aeromonas septicemia in fish. Although many virulence factors have been described, determining which factors are most important in pathogenesis is ongoing. To examine this further, the genomes of five Aeromonas strains isolated from various animals were sequenced and annotated in this study. Each isolate was further characterized using comparative genomic analyses and testing for production of selected virulence factors. Although previously identified as Aeromonas hydrophila, modern genotypic approaches including multilocus sequence typing and average nucleotide identity were used to determine identity. Four of five were confirmed to be A. hydrophila, but one isolate was identified as A. salmonicida. Virulence and antibiotic resistance genes in the five isolates were identified and compared to the curated genomes of forty-one other Aeromonas isolates. The distribution of virulence and antibiotic resistance genes among the 46 isolates was mapped using several bioinformatic tools. Isolates with similar virulence factor and antibiotic resistance genetic markers tended to originate from similar hosts or the environment, indicating common selective pressure. Challenge of Caenorhabditis elegans with different Aeromonas strains resulted in varying degrees of lethality as measured by nematode survival, and supported the existence of pathotypes; however, no single common virulence factors was found to explain the difference between highly virulent strains and those significantly less virulent. The results indicated that 1) a primary virulence factor responsible for the high degree of virulence remains unknown, or 2) virulence is the result of varying combinations of multiple factors, or 3) a mixed infection of pathotypes is needed to enable low virulent strains to be virulent.

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