Photobacterium damselae subsp. damselae, an abundant generalist marine pathogen, has been reported in various cetaceans worldwide. It is usually regarded as a secondary pathogenic agent, co-infecting alongside cetacean-associated viruses, yet it is seldom found to be the lead cause of fatal infection in marine cetaceans. Here we report a bottlenose dolphin that was found stranded on a beach in Ashdod, Israel, with a severe case of chronic suppurative pneumonia and splenic lymphoid depletion, in which Photobacterium damselae subsp. damselae (Phdd) was the sole bacterial pathogen detected. The assembly was deposited to the pubMLST P. damselae database under identification no. 91. We obtained the allelic MLST profile by using the BioNumerics Sequence Extraction Tool (Applied Maths) and according to the P. damselae scheme based on 6 housekeeping genes (glpF, gyrB, metG, pntA, pyrC, and toxR).1 This tool was also used for extraction of virulence factor gene sequences dly (GenBank accession no. 9937366) and hlyApl (GenBank accession no. ID 9937197). Hemolysis was tested by culturing the isolate on 5% sheep blood agar for 24 h at 37°C. Identification of P. damselae subsp. damselae was supported and confirmed by molecular, phenotypic, and genomic characterization. The 16S rRNA sequence exhibited a similarity of 99.17% with other P. damselae subsp. damselae strains in GenBank. When tested for hemolysis, the isolate exhibited a weak hemolytic phenotype, producing narrow halos on sheep blood agar plate. This phenotype is typical of P. damselae subsp. damselae lacking the pPHDD1 plasmid and that harbors the chromosomal PhlyC gene (hlyAch). WGS of the hemolytic genes dly and hlyApl yielded only the hlyA sequence, which showed 99% identity to the hlyAch sequences in GenBank. To the furthest of our knowledge, this is the first case of Phdd infection leading to fatal pneumonia reported in a dolphin from the eastern Mediterranean Sea. Furthermore, the isolate was closely related to isolates obtained from bottlenose dolphins in Italy, an indication of social ties between subpopulations of these dolphins from the respective regions. Therefore, we deem these findings important to the cross-regional conservation efforts.
*Presenting author
Literature Cited
1. Alba P, Caprioli A, Cocumelli C, Alba P, Caprioli A, Cocumelli C, Ianzano A, Donati V, Scholl F, Sorbara L, Terracciano G, Fichi G, Di Nocera F, Franco A, Battisti A. A new multilocus sequence typing scheme and its application for the characterization of Photobacterium damselae subsp. damselae associated with mortality in cetaceans. Front Microbiol. 2016;7:1656.