DIVERSITY AND DISTRIBUTON OF VIBRIO PARAHAEMOLYTICUS, A BACTERIOPLANKTON SPECIES OF CONCERN FOR HUMAN HEALTH, IN RHODE ISLAND

Author

Annie M. Cox, University of Rhode Island

Date of Award

2011

Degree Type

Dissertation

Degree Name

Doctor of Philosophy in Oceanography

Department

Oceanography

First Advisor

Marta Gomez-Chiarri

Abstract

Vibrio parahaemolyticus, a naturally occurring bacterium in coastal marine environments, can cause a severe gastrointestinal illness in humans when contaminated raw or undercooked seafood is consumed. Because of their potential for human illness, V. parahaemolyticus pose a threat to aquaculture through loss of business due to unfavorable publicity. Very little is known about V. parahaemolyticus in Narragansett Bay (Rhode Island); the only recently published study found a low concentration of total V. parahaemolyticus in Narragansett Bay water in the 1980s, and no pathogenic (Kanagawa-positive) strains were isolated. Thus far, illnesses due to V. parahaemolyticus in Rhode Island and the Northeast in general are exceptionally rare. Vibrio parahaemolyticus densities, however, are often correlated with warmer water temperatures and a likely climate-related rise in water temperature has been recorded in Narragansett Bay. The purpose of this study was to examine the ecology of V. parahaemolyticus, including spatial and temporal variability, and to determine which environmental factors are predictive of high levels of total and pathogenic V. parahaemolyticus in coastal salt ponds and Narragansett Bay. To determine V. parahaemolyticus concentration in water and oyster samples, a most probable number quantitative polymerase chain reaction method was used that detects the thermolabile hemolysin gene (tlh) for total V. parahaemolyticus and the thermostable-related hemolysin gene (trh) and/or thermostable direct hemolysin gene (tdh) for pathogenic V. parahaemolyticus. Potentially pathogenic (trh+/tdh+) V. parahaemolyticus strains were detected in Rhode Island oysters and waters for a period of approximately 15 weeks during the summers of 2009 and 2010, with peak levels usually detected in late July- early August. Peak densities found in Rhode Island coastal waters were similar to those found in other US coastal waters (total and pathogenic V. parahaemolyticus less than 10⁴ MPN g^-1). The relative percentage of pathogenic to total V. parahaemolyticus was highly variable depending on the site and time of sampling, and can be as high as 100%. Most pathogenic strains detected in Rhode Island were trh+, as opposed to the predominance of tdh+ or trh+ltdh+ strains in areas where most recent outbreaks have occurred, such as the Pacific Northwest and Gulf of Mexico. The genetic profile of trh+ and/or tdh+ strains of V. parahaemolyticus found in Rhode Island in 2010 was evaluated and compared to selected clinical strains using repetitive extragenic palindromic PCR (Rep-PCR). Similar to other studies on genetic diversity of V. parahaemolyticus, cluster analysis of Rep-PCR profiles of Rhode Island strains showed a very high level of genetic diversity in V. parahaemolyticus. None of the Rhode Island isolates closely clustered with pandemic strains.

For both 2009 and 2010, levels of tlh+ V. parahaemolyticus in oyster and water showed a significant, positive relationship with water temperature, explaining 16.7% of the variability in oyster tlh+ and 16.0% of the variability in water tlh+. Results for densities of pathogenic trh+ V. parahaemolyticus in oyster and water were consistent with the results for tlh+, showing a significant, positive relationship with temperature. For tdh+ densities, results were different. Oyster tdh+ showed a significant, negative relationship with salinity and water tdh+ showed a significant, inverse relation with turbidity. Due to the presence of potentially pathogenic strains in Rhode Island oysters and waters, farmers and shellfisherman need to take appropriate precautions to ensure a safe product for consumers, such as adequate post-harvest handling of the product at times when water temperatures are above 18°C. Further studies on the virulence of strains present in Rhode Island waters would help clarify the risk of illness to humans.

Ballast water is considered a route of introduction of human pathogens such as V. parahaemolyticus and V. cholerae. The effect of treating ballast water with chlorine dioxide (ClO₂) to stop invasive species on bacterial communities was determined using Terminal Restriction Fragment Length Polymorphism (T-RFLP). Results showed that the bacterial community re-emerged after Cl02 treatment, and that this community had a reduced diversity by comparison with the bacterial community in untreated ballast water. The bacterial assemblage that emerged after ClO₂ treatment was made up of original community members and previously undetected members. The previously undetected members are likely resultant from bacteria that are not affected by the treatment by virtue of being protected in some refuge (sediments, biofilms, etc.) in the tanks.

Recommended Citation

Cox, Annie M., "DIVERSITY AND DISTRIBUTON OF VIBRIO PARAHAEMOLYTICUS, A BACTERIOPLANKTON SPECIES OF CONCERN FOR HUMAN HEALTH, IN RHODE ISLAND" (2011). Open Access Dissertations. Paper 1702.
https://digitalcommons.uri.edu/oa_diss/1702