Histological features of Rickettsia-like organisms in the European flat oyster (Ostrea edulis L.)

AbstractThe European flat oyster (Ostrea edulis L.) represents an economically important oyster production in Southern Italy, widespreadin natural beds along the coast. The practice to be eaten raw is an everlasting concern for possible health risk with a need tostringently monitor the health of aquatic environment. A screening survey using histopathological examination was undertakenby harvesting O. edulis from different sites along the Apulian coast of Italy. Tissue samples of the digestive gland, kidney, gonad,and gill were provided for morphologic study in light microscopy (LM), transmission electron microscopy (TEM), and scanningelectron microscopy (SEM) analysis. The LM observations revealed spherical cytoplasmic inclusions as basophilic prokaryotecolonies in 13/250 oysters. The TEM and SEM confirmed the presence of intracytoplasmic inclusions of Rickettsia-like organ-isms (RLOs), merely in the epithelial cells of the digestive gland tubule tissues in the 13 oysters. Within intracytoplasmicvacuoles, RLOs exhibited a prokaryotic characteristic ultrastructure with transverse binary fission, a DNA zone full of chromatinfibers and a granular periplasmic ribosome zone. O. edulis were found positive for RLOs in wild oysters from Manfredonia, whilethe other sites were found free of pathological inclusions. Thus, we present the first report of a Rickettsia-like infection in theApulian wild oyster (O. edulis) from Italy, including an ultrastructural description and pathological characterization.