types, the fi rst four of which were the major patterns and accounted for
91.25% of the domestic clinical isolates. The RAPD typing patterns were
correlated with previously reported PFGE typing patterns (Wong et al.,
1996) of these isolates.
The O3:K6 Pandemic Clone
Honda et al. (1987) were the fi rst to report on the isolation of KP -
clinical isolates of V. parahaemolyticus belonging to the serovar O3:K6.
The occurrence of food-borne disease outbreaks in Taiwan increased
dramatically in 1996 (Chiou et al., 2000). This increase was correlated with
a high rate of isolation of V. parahaemolyticus , which caused 69 to 71% of the
total outbreaks from 1996 to 1999. Serotyping of 3,743 V. parahaemolyticus
isolates yielded 40 serovars, the most frequent of which was O3 : K6 (Chiou
et al., 2000).
Okuda et al . (1997b) examined 134 strains isolated from 1994 to 1996
in Calcutta with respect to serovar, the presence of the tdh gene and the
tdh -related hemolysin genes trh1 and trh2. All of the serovar O3 : K6 strains
carried the tdh gene but not the trh genes and did not produce urease.
RAPD analysis indicated that the O3:K6 serovar strains belonged to
a unique clone. Clinical O3:K6 strains isolated between 1982 and 1993
from travelers arriving in Japan from Southeast Asia were found to be
RAPD distinct from the Calcuttta O3 : K6 clone, while strains isolated in
1995 and 1996 were indistinguishable from the Calcutta O3:K6 strains.
These results suggested that the unique O3 : K6 clone may have become
prevalent not only in Calcutta but also in Southeast Asia. The O3:K6
serovar is considered more highly infectious than other serovars with up
to 75% of exposed individuals becoming infected compared to 56% with
other serovars (Daniels et al ., 2000).
Meyers et al. (2003) described the development and use of a set of
primers specifi c for a 369-bp sequence of ORF8 designated F-03MM824
effective in rapidly screening and detecting newly acquired isolates of V.
parahaemolyticus from marine waters from the Gulf of Mexico for the 03 : K6
serovar. These authors concluded that since all newly emerged O3:K6
isolates are derived from a single clone, it is likely that this strain has been
transported from one geographic local to another via ship ballast water.
The fi rst reported outbreak of gastroenteritis due to V . parahaemolyticus
serovar O3:K6 in North America occurred between May 31 and July 10,
1998. The outbreak involved 416 individuals in 13 states who had eaten
raw oysters harvested from Galvaston Bay, Texas and Long Island Sound
(Daniels et al ., 2000; Gendel et al ., 2001). Matsumoto et al. (2000) showed
with RAPD analysis that O3 : K6 strains from six countries including the
U.S. isolated from 1997 and later belong to the same clone.