Graduation Year

2008

Document Type

Dissertation

Degree

Ph.D.

Degree Granting Department

Biology

Major Professor

Valerie J. Harwood, Ph.D.

Keywords

Real-time PCR, BOX PCR, ViuB, Vcg, 16S rRNA

Abstract

The bacterium Vibrio vulnificus is an autochthonous inhabitant of estuarine waters and also found in shellfish such as oysters. It is a human pathogen of importance in the seafood industry, and can also infect recreational water users. Currently, recognized methods of detection rely upon isolation of pure cultures which requires at least 24 hours. To reduce the time needed for identification of the pathogen and simultaneously ascertain the virulence potential of the strains present, real-time PCR assays and sample processing procedures were developed (Chapter 1). These assays discriminate between type A (environmental, generally lower virulence) and type B (clinical, higher virulence) isolates.

The genetic relationships between environmental V. vulnificus strains isolated from permitted and prohibited shellfish harvesting areas was determined using BOX-PCR genomic fingerprinting coupled with sequence analysis of three proposed virulence markers: (1) the virulence correlated gene (vcg), (2) 16S rRNA type and (3) presence/absence of the vulnibactin gene (viuB) (Chapter 2). The real-time PCR assays were able to detect the presence of seeded V. vulnificus in environmental water at a concentration of 160 cells 100·ml?¹. In seeded oyster homogenates, the assays were able to detect a minimum of 10³ cells and 10² cells per reaction of type A and type B respectively. The phylogenetic analysis separated the majority of type A/ vcgE strains isolated from permitted shellfish harvesting areas from those isolated from prohibited harvesting areas. The genomic (BOX-PCR) fingerprints of type A and type AB isolates were more similar to one another than to type B isolates.

Only one type A/ vcgE isolate contained the viuB gene; however, eight type B/ vcgC isolates had that gene. No obvious grouping was discerned between type B/ vcgC isolates from permitted versus prohibited shellfish harvesting areas or between those possessing the viuB gene versus those lacking viuB. These data provide insight into the ecology and correlation between population biology and general water quality, as gauged by the classification of the shellfish growing area waters. The 16S typing assays can be used for routine rapid typing to aid in risk assessment and reduce infection frequency through consumption of contaminated seafood.

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