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Journal of Clinical Microbiology, February 2000, p. 578-585, Vol. 38, No. 2
Center for Southeast Asian Studies, Kyoto
University, Yoshida, Sakyo-ku, Kyoto,1
Osaka Prefectural Institute of Public Health, Higashinari-ku,
Osaka,2 and Department of Bacteriology,
School of Medicine, University of the Ryukyus, Nishihara,
Okinawa,3 Japan; Department of
Microbiology, National Institute of Cholera and Enteric Diseases,
Calcutta 700 010, India4; Department of
Microbiology, Soochow University, Taipei 11102, Taiwan5; U. S. Food and Drug
Administration, Dauphin Island, Alabama
36528-01586; Department of
Microbiology, College of Medicine, Pusan National University, Pusan
602-739, Korea7; and International
Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka 1000, Bangladesh8
Received 26 July 1999/Returned for modification 8 October
1999/Accepted 13 November 1999
Vibrio parahaemolyticus O3:K6 strains responsible for
the increase in the number of cases of diarrhea in Calcutta, India, beginning in February 1996 and those isolated from Southeast Asian travelers beginning in 1995 were shown to belong to a unique clone characterized by possession of the tdh gene but not the
trh gene and by unique arbitrarily primed PCR (AP-PCR)
profiles (J. Okuda, M. Ishibashi, E. Hayakawa, T. Nishino, Y. Takeda,
A. K. Mukhopadhyay, S. Garg, S. K. Bhattacharya, G. B. Nair, and M. Nishibuchi, J. Clin. Microbiol. 35:3150-3155, 1997).
Evidence supporting a hypothesis that this clone emerged only recently
and is spreading to many countries was obtained in this study. Of 227 strains isolated in a hospital in Bangladesh between 1977 and 1998, only 22 strains isolated between 1996 and 1998 belonged to the new
O3:K6 clone (defined by the serovar, the tdh and
trh typing, and AP-PCR profiles). The O3:K6 strains
isolated from clinical sources in Taiwan, Laos, Japan, Thailand, Korea,
and the United States between 1997 and 1998 were also shown to belong
to the new O3:K6 clone. The clonality of the new O3:K6 strains was also
confirmed by analysis of the toxRS sequence, which has been
shown to be useful for phylogenetic analysis of the members of the
genus Vibrio. The toxRS sequences of the
representative strains of the new O3:K6 clone differed from those of
the O3:K6 strains isolated before 1995 at least at 7 base positions
within a 1,346-bp region. A new PCR method targeted to 2 of the base
positions unique to the new O3:K6 clone was developed. This PCR method
could clearly differentiate all 172 strains belonging to the new O3:K6
clone from other O3:K6 strains isolated earlier. One hundred sixty-six
strains belonging to 28 serovars other than O3:K6 were also examined by
the new PCR method. The tdh-positive and
trh-lacking strains that belonged to the O4:K68 and O1:K
untypeable serovars and were isolated in three countries and from
international travelers beginning in 1997 gave positive results. The
AP-PCR profiles of these strains were nearly identical to those of the
new O3:K6 clone, and their toxRS sequences were 100%
identical to that of the new O3:K6 clone. The results suggest that
these strains may have diverged from the new O3:K6 clone by alteration
of the O:K antigens. In conclusion, this study presents strong evidence
for the first pandemicity in the history of V. parahaemolyticus and reports a novel toxRS-targeted PCR method that will be useful in epidemiological investigation of the cases associated with the current pandemic spread.
0095-1137/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Pandemic Spread of an O3:K6 Clone of Vibrio
parahaemolyticus and Emergence of Related Strains Evidenced by
Arbitrarily Primed PCR and toxRS Sequence Analyses
*
Corresponding author. Mailing address: Center for
Southeast Asian Studies, Kyoto University, 46 Shimoadachi-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Phone: 81-75-753-7367. Fax:
81-75-753-7350. E-mail:
nishibuc{at}mb.med.kyoto-u.ac.jp.
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