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چکیده
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The Wildlife and Aquatic Veterinary Disease Laboratory received bacterial colonies on blood agar from two sharks in 2014. Colonies were isolated from brain, inner ear, and inflamed subcutaneous tissues surrounding the endolymphatic ducts of a juvenile common thresher shark (Alopias vulpinus), and from brain and peri-endolymphatic tissues of a juvenile salmon shark (Lamna ditropis). The two sharks were among 15 (12 salmon; 3 thresher) that stranded on CA beaches between 2011 and 2014, and were necropsied by the CADFW. Colonies were subcultured and subjected to biochemichal, phenotypic and molecular analyses. Based on morphological and biochemical characteristics, bacterial isolates were identified as Carnobacterium maltaromaticum. C. maltaromaticum is a gram positive rod that has been isolated from various sources. This bacterium inhibits growth of foodborne pathogens such as Listeria monocytogenes due to its ability to produce bacteriocins. Viable and heat-treated C. maltaromaticum have been used as protective cultures in various meat and seafood products. Sequence analysis of the 16S ribosomal RNA gene of all five shark isolates produced 1420 bp amplicons with identical sequences.The 16S rRNA gene sequences shared 99.7% (1416/1420 bps) identity with a C. maltaromaticum isolated from ripened cheese, and 99.7% (1013/1016 bps) sequence identity with C. maltaromaticum previously reported from 19 CA salmon sharks that stranded in 2002-2008. Identification of C. maltaromaticum in subcutaneous tissues surrounding the endolymphatic ducts of thresher and salmon sharks indicates that bacteria likely gain access to the inner ear and brain via the endolymphatic ducts. Genetic homology between C. maltaromaticum from sharks and the isolate from one human food source suggests that an anthropogenic etiology for CA shark strandings is at least a possibility. Determining whether or not the actual cause of otitis and meningoencephalitis in sharks stems from natural sources or aquatic
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