Population structure of clinical Vibrio parahaemolyticus from 17 coastal countries, determined through multilocus sequence analysis

Abstract

Vibrio parahaemolyticus is a leading cause of food-borne gastroenteritis worldwide. Although this bacterium has been the subject of much research, the population structure of clinical strains from worldwide collections remains largely undescribed, and the recorded outbreaks of V. parahaemolyticus gastroenteritis highlight the need for the subtyping of this species. We present a broad phylogenetic analysis of 490 clinical V. parahaemolyticus isolates from 17 coastal countries through multilocus sequence analysis (MLST). The 490 tested isolates fell into 161 sequence types (STs). The eBURST algorithm revealed that the 161 clinically relevant STs belonged to 8 clonal complexes, 11 doublets, and 94 singletons, showing a high level of genetic diversity. CC3 was found to be a global epidemic clone of V. parahaemolyticus, and ST-3 was the only ST with an international distribution. recA was observed to be evolving more rapidly, exhibiting the highest degree of nucleotide diversity (0.028) and the largest number of polymorphic nucleotide sites (177). We also found that the high variability of recA was an important cause of differences between the results of the eBURST and ME tree analyses, suggesting that recA has a much greater influence on the apparent evolutionary classification of V. parahaemolyticus based on the current MLST scheme. In conclusion, it is evident that a high degree of genetic diversity within the V. parahaemolyticus population and multiple sequence types are contributing to the burden of disease around the world. MLST, with a fully extractable database, is a powerful system for analysis of the clonal relationships of strains at a global scale. With the addition of more strains, the pubMLST database will provide more detailed and accurate information, which will be conducive to our future research on the population structure of V. parahaemolyticus.

Figure 1. V. parahaemolyticus “population snapshot” obtained using eBURST v3.

Eight clonal complexes (CC3, CC345, CC83, CC8, C120, CC527, CC332 and CC890), 11 doublets (D1 to D11), and 94 singletons were identified. STs that are SLVs of each other are connected by red lines. DLV STs are connected by blue lines. The sizes of the circles are relative to the number of strains in the ST.

Figure 2. An ME tree was constructed using the concatenated sequences of the seven loci of each of the 161 STs obtained in this study.

Squares, circles, and triangles with different shading represent the eight clonal complexes observed via eBURST. The scale represents the evolutionary distance, and bootstrap values over 50% are shown on the branches.