Discussion
In this study, 15 different serotypes of V. parahaemolyticus were
identified among the isolates recovered. As a traditionally used method
for the characterization of V. parahaemolyticus, serotyping failed to
reveal the depth of genetic and clonal relationships among isolates.
It is known that different bacterial serotypes can share common
molecular types, such as the MLST profiles (Chao et al., 2009). In
this study, several isolates belonging to genetically distant STs
shared the same serotype, and isolates with the same STs displayed
different serotypes, which suggested that MLST better resolves the
phylogenetic relatedness of V. parahaemolyticus isolates than
serotyping alone; this resolution is essential for investigation of
bacterial population structures, and can provide valuable informa-
tion about the emergence of new epidemic clones.
In this study, 20 singletons were identified among the 31 STs
using eBURST. These singletons are currently not part of any recog-
nized clonal complex. Seventeen STs previously unidentified were
observed in this study; this result was confirmed by the curator of
PubMLST database. New STs were recovered from the patient and
related seafood products. The newly discovered ST-787, belonging
to CC3 [SLV (pyrC)], suggesting that the housekeeping genes within
isolates of CC3 are continuing to evolve. Previous study suggested
the recA gene was highly diverse (Yu et al., 2011). A recombination
test performed as part of this study also showed that the recA and
dtdS loci displayed higher nucleotide diversity than the other five
loci. The “standardized” index of association (IAS) of the entire
isolate collection was 0.8787, indicating that the alleles were in
linkage disequilibrium or were nonrandomly distributed
(Table 2). It was consisted with previous study that a nonrandom
distribution of alleles in the V. parahaemolyticus population is
general, although recombination may also be occurring within
different subpopulations (Gonzalez-Escalona et al., 2008).