Characterization of Photobacterium damselae Causing Seafood-Associated Histamine Poisoning = 수산물 관련 히스타민 식중독을 유발하는 Photobacterium damselae의 특성 분석

다국어 초록 (Multilingual Abstract)

Photobacterium damselae (PD) is recognized as a significant marine bacterium implicated in both aquatic animal diseases and seafood-associated histamine poisoning. However, PD strains originating from marine mammals remain poorly characterized, and their potential contributions to foodborne histamine accumulation have not been thoroughly examined. In this study, a comprehensive characterization was conducted on a Photobacterium damselae subsp. damselae (PDD) strain GCUPdd, isolated from a free-ranging spotted seal (Phoca largha) stranded in Korea. Microbiological and pathological analyses indicated that the bacterium was likely involved in a systemic infection in the spotted seal. Whole-genome sequencing revealed that GCUPdd carried a pPHDD1-like virulence plasmid and encoded multiple pathogenicity factors, including damselysin, phobalysin, phospholipase, and elements of the type VI secretion system (T6SS). Importantly, PDD strain GCUPdd possessed a complete histidine decarboxylase gene cluster associated with histamine fish poisoning and demonstrated markedly elevated histamine-producing capacity compared with the reference PDD strain under conditions simulating inadequate cold chain management instead of proper refrigeration and freezing. Furthermore, Cell cytotoxicity assays additionally demonstrated that this isolate exhibits considerable toxicity towards human cell lines, underscoring its potential as a zoonotic pathogen. Collectively, this study highlights GCUPdd as a PDD strain with both strong pathogenic traits and a high histamine-producing ability, suggesting that PDD contamination may pose combined ecological, veterinary, and food safety risks. These findings expand current knowledge of PDD in marine mammals and provide valuable insights into its role as a histamine-producing hazard associated with seafood.

목차 (Table of Contents)

• Ⅰ. Introduction 1
• 1. Photobacterium damselae 1
• 2. Histamine fish poisoning 2
• 3. Spotted seal (Phoca largha) 2
• 4. Purpose of this study 3
• Ⅱ. Materials and methods 4
• 1. Characterization of Photobacterium damselae 4
• 1.1. Case description 4
• 1.2. Bacterial isolation and identification 5
• 1.3. PCR-based organ screening for Photobacterium damselae 6
• 1.4. Antimicrobial susceptibility testing 7
• 1.5. Whole genome sequencing and genomic characterization 8
• 1.6. Histamine production assay for the Photobacterium damselae isolate 10
• 1.7. Bacterial cell cytotoxicity assay 11
• 2. Culture deposition and genome submission 12
• Ⅲ. Results 13
• 1. Gross lesions and histopathology 13
• 2. Evidence suggesting presumptive systemic PDD infection in spotted seal 15
• 3. Virulence-related features identified in the genome of PDD strain GCUPdd 20
• 4. Strong histamine-producing ability identified in PDD strain GCUPdd 33
• 5. Potential cell cytotoxic effects observed in PDD strain GCUPdd 35
• Ⅳ. Discussion 37
• Ⅴ. Conclusion 41
• Ⅵ. References 42
• 국문 초록 46