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Although several Edwardsiella tarda infections have been reported, its pathogenic role in marine mammals has not been investigated at the genome level. We investigated the genome of E. tarda strain KC-Pc-HB1, isolated from the false killer whale (Pseudorca crassidens) found bycaught in South Korea. The obtained genome was similar to that of human pathogenic E. tarda strains, but distinct from other Edwardsiella species. Although type III and VI secretion systems, which are essential for the virulence of other Edwardsiella species, were absent, several virulence-related genes involved in the pathogenesis of E. tarda were found in the genome. These results provide important insights into the E. tarda infecting marine mammals and give valuable information on potential virulence factors in this pathogen.

The emergence of antimicrobial resistant (AMR) strains of Morganella morganii is increasingly being recognized. Recently, we reported a fatal M. morganii infection in a captive bottlenose dolphin (Tursiops truncatus) bred at a dolphinarium in South Korea. According to our subsequent investigations, the isolated M. morganii strain KC-Tt-01 exhibited extensive resistance to third-generation cephalosporins which have not been reported in animals. Therefore, in the present study, the genome of strain KC-Tt-01 was sequenced, and putative virulence and AMR genes were investigated. The strain had virulence and AMR genes similar to those of other M. morganii strains, including a strain that causes human sepsis. An amino-acid substitution detected at the 86th residue (Arg to Cys) of the protein encoded by ampR might explain the extended resistance to third-generation cephalosporins. These results indicate that the AMR M. morganii strain isolated from the captive dolphin has the potential to cause fatal zoonotic infections with antibiotic treatment failure due to extended drug resistance, and therefore, the management of antibiotic use and monitoring of the emergence of AMR bacteria are urgently needed in captive cetaceans for their health and conservation.

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Erysipelas, caused by Erysipelothrix rhusiopathiae, is considered one of the most serious infectious diseases of captive and free-ranging cetaceans worldwide, as these animals are known to be highly susceptible to the bacterial infections. The potential diversity between E. rhusiopathiae isolates from captive cetaceans has been previously described; however, the microbiological features of the free-ranging cetacean isolates remain unclear. Here, we describe a case of bacteremia in a rough-toothed dolphin (Steno bredanensis) caused by E. rhusiopathiae. Additionally, we present the first genomic features of the bacteria from free-ranging cetacean individuals. Histopathological and microbial examinations revealed that E. rhusiopathiae caused bacteremia and systemic infection in the dolphin. The genome of the isolated E. rhusiopathiae strain KC-Sb-R1, which was classified as Clade 1 possessing SpaB gene, was clearly differentiated from the other swine-isolated E. rhusiopathiae, and the comparison of its serovar-defining chromosomal region revealed that our isolate was greatly similar to those of other previously reported serovar 2/15 isolates, including the captive-dolphin isolate. Moreover, most of the potential virulence factors in the strain KC-Sb-R1 were similar to those in the strain Fujisawa. Further, a potential cytotoxicity of the isolate was confirmed, suggesting that marine mammal-isolated E. rhusiopathiae could possess strong pathogenic potential in other animals, including humans. These results would further increase our understanding on the risk factors for controlling zoonotic pathogens of emerging infectious diseases in captive or free-ranging cetaceans, and also provide important insight into the diversity of E. rhusiopathiae in animals.