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Ships' Ballast as a Potential Vector for the Transfer of Antibiotic Resistance Genes Among Estuarine Environments

EPA Grant Number: U915900
Title: Ships' Ballast as a Potential Vector for the Transfer of Antibiotic Resistance Genes Among Estuarine Environments
Investigators: III, Frank Thomson
Institution: Old Dominion University
EPA Project Officer: Boddie, Georgette
Project Period: August 20, 2001 through August 19, 2004
Project Amount: $88,605
RFA: STAR Graduate Fellowships (2001)
Research Category: Academic Fellowships

Description:

Objective:

Ships' ballast has been implicated as a vector for the dispersal of invasive species into new environments. Numerous cases have been documented for the introduction of macroorganisms via ballasting operations, but what is less known is the role of ballast water and residuals in the spread of potentially harmful microbes, especially with reference to novel genotypes (Ruiz et al., 2000). Of particular interest are the genes encoding for various forms of antibiotic resistance, many of which are carried on mobile genetic elements. A three-year sampling effort has yielded over 300 putative isolates of Vibrio cholerae from ships' ballast tanks and various environmental sources, of which 208 have been profiled for antibiotic susceptibility using twelve diverse antibiotics. The results demonstrate widespread resistance to β-lactams (74.6%), with isolated instances of resistance to other antibiotics. Plasmid extractions and restriction enzyme analyses have shown the presence of an ostensible plasmid of approximately 60 kbp in many of these isolates. Additional work is being done using restriction fragment length polymorphisms and PCR for specific antibiotic resistance genes in an attempt to characterize these plasmids. Knowledge from this study and future microcosm experiments will help us to ascertain the potential for horizontal gene transfer in a ballast tank setting.

To determine the phenotypic and genotypic character of antibiotic resistance in Vibrio cholerae isolated from ships’ ballast tanks and environmental sources.

Approach:

Antibiotic susceptibility analyses were conducted using the disk diffusion method to determine the phenotypic patterns of antibiotic resistance in isolates of Vibrio cholerae.  These isolates were putatively designated V. cholerae based on biochemical results from the method of Choopun et al. (2001) and are being molecularly confirmed according to the PCR method of Chun et al. (2000).  Subsequent molecular tests are being conducted to determine the genotypic character of antibiotic resistance.  Plasmid and genomic DNA extractions were used to isolate chromosomal and extrachromosomal plasmid DNA, respectively.  These DNA fractions are subjected to restriction enzyme analyses and PCR for specific antibiotic resistance genes in an effort to link our observed antibiotic resistance patterns to specific genetic mechanisms.

Supplemental Keywords:

Microbial ecology, ballast water, Vibrio cholerae, antibiotic resistance,
Relevant Websites:

None.

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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