Date of Award

Summer 7-20-2015

Degree Type

Thesis

Degree Name

Master of Science in Integrative Biology (MSIB)

Department

Biology

Major Professor

Dr. Donald McGarey

First Committee Member

Dr. Melanie Griffin

Second Committee Member

Dr. Martin Hudson

Abstract

Aeromonas hydrophila is a Gram-negative, bacterial pathogen of humans and other vertebrates. To delineate pathotypes, the genomes of twenty-eight Aeromonas isolates were screened by PCR to determine the presence of virulence factors including: aerolysin (aerA), cytotoxic enterotoxin (act), hemolysin (ahh1), elastase (ahyB), enolase (eno), S-layer protein (ahsA), serine protease (ser), Type IV Aeromonas pilus (tapA), lipase (lip), and Type Three Secretion System (T3SS) components (aopB, ascV). Genes for ahh1, lip, ser, and ahyB were present in all 28 strains tested, others genes varied. The tapA gene encoding a type IV pilus was absent in all 28 isolates screened. After the presence or absence of these genes was determined, corresponding activity was determined using phenotypic assays. Analysis of the data defined 11 different pathotypes based on the genotypic and phenotypic profiles with the largest cluster being ahh1+, ahyB+, lip+, ser+, act+, aerA+, eno-, aopB-, ascV-, ahsA-, and tapA-. Representatives of the pathotype groups were used in a nematode challenge assay and a cell culture assay to assess the importance of virulence factors in their pathogenicity and their cytotoxicity, respectively. All Aeromonas strains tested, with the exception of A. hydrophila ML09-119, showed significantly greater lethality compared to the E. coli negative control in the nematode challenge, yet only A. hydrophila 1127 was significantly more lethal than the positive control Pseudomonas aeruginosa PAO1. Variation in lethality between A. hydrophila strains suggests that C. elegans is a suitable model for studying pathogenic mechanisms and elucidating the combination of factors that define highly virulent strains.

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