Molecular Identification of Photobacterium damselae in Wild Marine Fish from the Eastern Mediterranean Sea

Infectious diseases caused by marine bacterial pathogens inflict increasing economic losses to fisheries and aquaculture, while also posing a growing risk to public health and affected species conservation. In this study, four wild marine fish species were collected at five fishing sites in Israel, divided into two regions-north (Acre, Haifa, Shefayim) and center-south (Tel-Aviv and Ashdod), and screened for Photobacterium damselae. An initial screening was carried out using PCR analysis with specifically designed primers on DNA extracted from livers and kidneys. P. damselae-positive samples had their 16S rRNA amplicons sequenced. Later, an attempt to specify relevant sub-species was performed, using a three-layered gene screen: Car, ureC and toxR. Of 334 fish samples, 47 (14%) were found to be P. damselae-positive, of which 20 were identified as P. damselae subsp. piscicida (Phdp), two as P. damselae subsp. damselae (Phdd) and 25 could not be identified to subspecies. Our results strengthen the view that fish residing in a polluted environment are receptive of pathogenic microorganisms. To assess how the presence of pathogens may affect population management and conservation, this research should be followed by studies aimed at: (i) quantifying levels of pollutants that may affect pathogen emergence, and (ii) creating a standard pollution-level index as a basis for setting criteria, above which authorities should take measures of precaution.