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J. Bacteriol., Jun 1995, 3191-3198, Vol 177, No. 11
DK Karaolis, R Lan and PR Reeves
The DNA sequences of the asd genes from 45 isolates of Vibrio cholerae (19
clinical O1 isolates, 2 environmental nontoxigenic O1 isolates, and 24
isolates with different non-O1 antigens) were determined. No differences
were found within either sixth- or seventh-pandemic isolates; however,
variation was found between the two forms and among the non-O1 isolates.
O139 isolates had sequences identical to those of seventh-pandemic
isolates. Phylogenetic trees with Vibrio mimicus as the outgroup suggest
that the sixth-pandemic, seventh-pandemic, and U.S. Gulf isolates are three
clones that have evolved independently from different lineages of
environmental, nontoxigenic, non-O1 V. cholerae isolates. There is evidence
for horizontal transfer of O antigen, since isolates with nearly identical
asd sequences had different O antigens, and isolates with the O1 antigen
did not cluster together but were found in different lineages. We also
found evidence for recombination events within the asd gene of V. cholerae.
V. cholerae may have a higher level of genetic exchange and a lower level
of clonality than species such as Salmonella enterica and Escherichia coli.
Copyright © 1995, American Society for Microbiology
The sixth and seventh cholera pandemics are due to independent clones separately derived from environmental, nontoxigenic, non-O1 Vibrio cholerae
Department of Microbiology (GO8), University of Sydney, New South Wales, Australia.
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