This collaborative project represents the first attempt to thouroughly evaluate aggregates (also called marine snow) sampled from shallow coastal areas for the occurrence of pathogenic microbes. Results of our field survey clearly demonstrated that aggregates represent an important reservoir for bacterial pathogens belonging to the group Vibrio. Analyses revealed that aggregates concentrated bacteria up to four orders of magnitude when compared with seawater collected from the same site at the same time. Bacteria known to cause infections in humans (Vibrio vulnificus, V. parahaemolyticus, etc.) and in marine animals (V. splendidus, Aeromonas salmonicida) were significantly more prevalent in aggregates when compared to seawater.

GFP-transformed bacteria are significantly enriched in lab-made aggregates (right plate) as compared to seawater (left)

Using vitally-labeled P. marinus (coupled with confocal laser scanning microscopy and flow cytometry), we demonstrated that the uptake and dispersion of the parasite is mainly performed by hemocytes associated with gill and mantle tissues. We are currently focusing on the investigation of factors affecting the early interactions between bivalves and their waterborne pathogens (attachment, internalization) and expanded our focus to include the digestive route (aspects detailed in the next project).

Aggregates were experimentally produced and used in laboratory transmission studies of Perkinsus marinus and Vibrio pathogens

Laboratory transmission experiments are carried out to determine if aggregated pathogens are transmitted differently than free pathogens, and to investigate the specific role aggregates play in the delivery of pathogens to the site of entry. Our experimental pathogens include Perkinsus marinus, a protistan parasite that is fatal to the Eastern oyster (Crassostrea virginica) and Green Fluorescent Protein (GFP)-transformed strain of the bacterium Vibrio aestuarianus. Results of oyster challenge with P. marinus demonstrate the acquisition of this protist following exposure to parasite-laden aggregates.

Confocal Laser Scanning Microscopy represents an efficient technique to investigate the early steps of the invasion of bivalve hosts by their parasites