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EMERGING VIBRIO HARVEYI AND VIBRIO CAMPBELLII PATHOGENS IN GEORGIA’S CRASSOSTREA VIRGINICA OYSTERS AND MERCENARIA MERCENARIA CLAMS: PRESENCE, DISTRIBUTION, AND CONCENTRATIONS*

Abstract

In the face of global warming and ocean acidification, Vibrio pathogens are geographically expanding and rapidly evolving. V. harveyi and V. campbellii belong to the Harveyi clade and are similar upon their genetic make-up. Natively found in warm waters of Asia and South America, these species are well-established pathogens that infect fish, shrimp, and mollusks. Neither strain is pathogenic to humans, however farmed oysters and clams are a valuable commodity in Georgia. Due to the climate change, the Southeastern United States is potentially becoming an accommodating environment for these pathogens, however this has never been previously explored. It is crucial for Georgia waters to be tested and monitored for both strains because if present in high concentration it would significantly impact the aquaculture industry. Using reference strains of V. harveyi ATCC 14126 and V. campbellii ATCC BAA-1116 / BB120, seven previously described primers for species-specific detection of V. harveyi virulence genes (toxR, luxR, vhh, vhh(a), srp, vhp, and rpoA) were tested with both strains. All the seven genes were reliable detected in both reference strains. These signature genes were used for qPCR detection and quantitation of V. harveyi and V. campbellii in wild oysters and farmed clams collected at random from three sites around Townsend, GA. In summer 2022 monitoring, vhh(a) and vhp genes were consistently detected in both oysters and clams in the range of 102 to 1010 copy numbers per gram of tissue, and no vhh gene was ever detected. Distribution and concentrations of the other genes varied between three sites. These results evidenced high abundance of V. harveyi and V. campbellii in wild and farmed mollusks. They also evidenced that not all previously published target genes are reliable for detection of these pathogens, and suggested vhh(a) and vhp genes as best targets. Data obtained in a complimentary study evidenced their presence in water and sediments.

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