Characterization of Pathogenic Photobacterium damselae subsp. damselae From Whiteleg Shrimp (Litopenaeus vannamei): An Emerging Cause of Mass Mortality in the Republic of Korea

초록

Mass mortality events characterized by muscle whitening occurred in farmed whiteleg shrimp (Litopenaeus vannamei) in the Republic of Korea from July to September 2025. After ruling out the major crustacean pathogens listed by the World Organization for Animal Health (WOAH) through molecular screening, three dominant isolates of Photobacterium damselae subsp. damselae were recovered from the affected shrimp. The isolates were identified by 16S rRNA gene sequencing and confirmed by detection of the ureC gene. Phenotypic characterization showed that P. damselae subsp. damselae SNUABM-JN1 grew across a wide range of temperatures (10-40 degrees C) and salinities (0.5%-5.0%), with a shorter lag phase at 29 degrees C across the tested salinity range. In the challenge test, the median lethal dose (LD50) was estimated as 1.10 & times; 105 CFU & sdot;g-1 at 25 degrees C and 5.58 & times; 103 CFU & sdot;g-1 at 29 degrees C, indicating lower survival at the higher temperature. The characteristic clinical signs of muscle whitening were reproduced, and histopathology revealed coagulative necrosis and hemocytic infiltration in both muscle and hepatopancreatic tissues. Whole genome sequencing showed that P. damselae subsp. damselae SNUABM-JN1 possesses two chromosomes and four plasmids, with 4420 predicted genes. Genomic analysis identified 58 putative virulence-associated genes and seven antimicrobial resistance genes. In addition, six prophage regions were predicted, including one intact prophage carrying a ribosome-associated toxin gene (ratA), and 24 genomic islands were detected. Collectively, this study isolated and characterized P. damselae subsp. damselae SNUABM-JN1 from whiteleg shrimp with muscle whitening, reporting this infection in the Republic of Korea for the first time.

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