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Journal of Clinical Microbiology, May 1999, p. 1313-1318, Vol. 37, No. 5
Molecular Genetics Laboratory,
Received 9 November 1998/Returned for modification 30 December
1998/Accepted 12 February 1999
Vibrio cholerae O139 Bengal initially appeared in the
southern coastal region of Bangladesh and spread northward, causing explosive epidemics during 1992 and 1993. The resurgence of V. cholerae O139 during 1995 after its transient displacement by a
new clone of El Tor vibrios demonstrated rapid changes in the epidemiology of cholera in Bangladesh. A recent outbreak of cholera in
two north-central districts of Bangladesh caused by V. cholerae O139 led us to analyze strains collected from the
outbreak and compare them with V. cholerae O139 strains
isolated from other regions of Bangladesh and neighboring India to
investigate their origins. Analysis of restriction fragment length
polymorphisms in genes for conserved rRNA (ribotype) revealed that the
recently isolated V. cholerae O139 strains belonged to a
new ribotype which was distinct from previously described ribotypes of
toxigenic V. cholerae O139. All strains carried the genes
for toxin-coregulated pili (tcpA and tcpI) and
accessory colonization factor (acfB), the regulatory gene
toxR, and multiple copies of the lysogenic phage genome
encoding cholera toxin (CTX
0095-1137/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Molecular Characterization of a New Ribotype of
Vibrio cholerae O139 Bengal Associated with an Outbreak
of Cholera in Bangladesh
) and belonged to a previously described
ctxA genotype. Comparative analysis of the rfb
gene cluster by PCR revealed the absence of a large region of the
O1-specific rfb operon downstream of the rfaD
gene and the presence of an O139-specific genomic region in all O139
strains. Southern hybridization analysis of the O139-specific genomic
region also produced identical restriction patterns in strains
belonging to the new ribotype and those of previously described
ribotypes. These results suggested that the new ribotype of Bengal
vibrios possibly originated from an existing strain of V. cholerae O139 by genetic changes in the rRNA operons. In contrast
to previously isolated O139 strains which mostly had resistance to
trimethoprim, sulfamethoxazole, and streptomycin encoded by a
transposon (SXT element), 68.6% of the toxigenic strains analyzed in
the present study, including all strains belonging to the new ribotype,
were susceptible to these antibiotics. Molecular analysis of the SXT
element revealed possible deletion of a 3.6-kb region of the SXT
element in strains which were susceptible to the antibiotics. Thus,
V. cholerae O139 strains in Bangladesh are also undergoing
considerable reassortments in genetic elements encoding antimicrobial resistance.
*
Corresponding author. Mailing address: Molecular
Genetics Laboratory, Laboratory Sciences Division, ICDDR,B, GPO Box
128, Dhaka-1000, Bangladesh. Phone: 880 2 871751 to 880 2 871760. Fax: 880 2 872529 and 880 2 883116. E-mail: faruque{at}icddrb.org.
Journal of Clinical Microbiology, May 1999, p. 1313-1318, Vol. 37, No. 5
0095-1137/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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