Opportunistic Vibrio alginolyticus and six other Vibrio species from ready-to-eat seafood associated with the Korean coast: Public health implications as emerging human pathogens

Vibrio spp. are causative agents of gastrointestinal diseases, wound infection, and septicemia, primarily through consumption of or contact with contaminated seafood/water. However, little is known about the pathogenic traits of opportunistic Vibrio species: particularly in the context of their potential to cause human infections, rather than being considered solely as pathogens of aquatic animals. This study aimed to investigate the pathogenic potential and interspecies relationships of seven Vibrio spp. (V. cholerae, V. parahaemolyticus, V. vulnificus, V. alginolyticus, V. mimicus, V. fluvialis, and V. metschnikovii) in 502 ready-to-eat seafood samples spanning eight food categories, encompassing three major human pathogens and four occasional human pathogens. Vibrio detection was performed using two different isolation protocols—Protocol I (TCBS agar alone) and Protocol II (TCBS combined with mCPC agar)—followed by biochemical and genetic confirmation. In addition, the genetic virulence profiles and phylogenetic relationships of the isolates were examined. The overall detection rate of Vibrio spp. was 23.9 % (ca. 2.6 log), with species-dependent differences in detection efficacy by protocol (false-positive rates: I > II for V. cholerae (P < 0.05), I ≈ II for V. vulnificus (P > 0.05)), supporting the simplified use of TCBS agar alone, with emphasis on subsequent confirmatory identification. Among the identified species, V. alginolyticus—an opportunistic human pathogen—exhibited the widest distribution across various sample types (17.3 %; ca. 2.5 log), comparable to that of V. parahaemolyticus (11.4 %; ca. 2.8 log), with a weak positive correlation observed between these two species (Φ = 0.417, P < 0.001). In particular, high prevalence was observed in sashimi, such as gizzard shad and conger (typically consumed with the skin attached), as well as in cephalopods such as octopus (a benthic organism). In terms of virulence-associated genes, vcgC (70.6 %; clinical type) was predominantly detected in V. vulnificus isolates, tdh was detected in 1.8 % of V. parahaemolyticus, and none were detected in V. cholerae. Moreover, the majority of V. alginolyticus isolates (98.8 %) harbored all three categories of virulence genes involved in early-stages of host infection, including adherence, biofilm formation, and motility, indicating the presence of conserved pathogenic gene profiles among the strains. In addition, the V. alginolyticus isolates were grouped into four distinct clusters, indicating phylogenetic differentiation among the strains and a lack of phylogenetic affiliation with other reference Vibrio species. This pattern may reflect geographical characteristics associated with the coastal areas of South Korea, regardless of isolation source. The findings of this study provide comprehensive data on the co-occurrence of opportunistic Vibrio species in ready-to-eat seafood, which have been underrecognized and underregulated in South Korea compared with the three major species. Taken together, these results highlight the need for increased awareness and control of V. alginolyticus as an emerging human pathogen.