Genetic diversity of Vibrio vulnificus strains isolated in Korea

Hong Sa-hyun, Jung Su-Mi, Yun Young Sun, Na Hae-Young, Kang Byung Haek, Kim Jae Ok
Division of Bacterial Diseases, Center for Laboratory Control of Infectious Diseases, KCDC

Background: Vibrio vulnificus is a pathogenic bacterium naturally occurring in coastal and estuarine water worldwide that can cause life-threatening diseases by wound infection or food poisoning. The genetic background of V. vulnificus isolates thriving in Korea remains undefined.
Methodology: In this study, 42 isolates (25 clinical and 17 environmental) were considered for examining their genetic relationship and diversity in Korea between 2014 and 2015. Multilocus sequence typing (MLST) method was used to study the prevalence and population structure of clinical strains. PCR conditions of the ten housekeeping genes and sequence type (ST) determination of all isolates were followed as described in PubMLST. Conventional PCR assay was performed to determine the presence of vvhA and rtxA genes and for 16S rRNA typing. Genetic diversity analysis was carried out using the MEGA 6 software. Based on the related STs, the isolates were analyzed by neighbor-joining method.
Results: The 42 tested isolates belonged to 40 STs, each of which was new to the MLST database. The nucleotide diversity ranged from 0.017 (pntA) to 0.036 (lysA), and presented the largest number of variable sites (9.25%). Clinical and environmental (sea water) strains were distinguished by neighbor-joining tree constructed from STs.
Conclusion: Forty-two V. vulnificus clinical isolates showed 40 different STs, which were stored in PubMLST as new STs, suggesting a high level of genetic diversity. These results revealed genetic differences between the clinical and environmental strains.

Keywords: Vibrio vulnificus, Multilocus sequence typing (MLST), Housekeeping genes, Genetic diversity, Foodborne diseases