Tor Isolates Research Articles

Phylogenetic Diversity of Vibrio cholerae Associated with Endemic Cholera in Mexico from 1991 to 2008.

ABSTRACTAn outbreak of cholera occurred in 1991 in Mexico, where it had not been reported for more than a century and is now endemic. Vibrio cholerae O1 prototype El Tor and classical strains coexist with altered El Tor strains (1991 to 1997). Nontoxigenic (CTX−) V. cholerae El Tor dominated toxigenic (CTX+) strains (2001 to 2003), but V. cholerae CTX+ variant El Tor was isolated during 2004 to 2008, outcompeting CTX− V. cholerae. Genomes of six Mexican V. cholerae O1 strains isolated during 1991 to 2008 were sequenced and compared with both contemporary and archived strains of V. cholerae. Three were CTX+ El Tor, two were CTX− El Tor, and the remaining strain was a CTX+ classical isolate. Whole-genome sequence analysis showed the six isolates belonged to five distinct phylogenetic clades. One CTX− isolate is ancestral to the 6th and 7th pandemic CTX+ V. cholerae isolates. The other CTX− isolate joined with CTX− non-O1/O139 isolates from Haiti and seroconverted O1 isolates from Brazil and Amazonia. One CTX+ isolate was phylogenetically placed with the sixth pandemic classical clade and the V. cholerae O395 classical reference strain. Two CTX+ El Tor isolates possessing intact Vibrio seventh pandemic island II (VSP-II) are related to hybrid El Tor isolates from Mozambique and Bangladesh. The third CTX+ El Tor isolate contained West African-South American (WASA) recombination in VSP-II and showed relatedness to isolates from Peru and Brazil. Except for one isolate, all Mexican isolates lack SXT/R391 integrative conjugative elements (ICEs) and sensitivity to selected antibiotics, with one isolate resistant to streptomycin. No isolates were related to contemporary isolates from Asia, Africa, or Haiti, indicating phylogenetic diversity.

Genetic charaeterisation of tcpA: encoding an essential virulence factor in Vibrio cholerae

Cholera is a major public health problem, recently as an E1 Tor pandemic and now emergent as a new threat in the form of the O139 serotype. The toxin-coregulated pilus (TCP) has been shown to be an essential virulence factor capable of eliciting protective antibodies in the infant mouse cholera model. Biotype-specific antigenic differences have been demonstrated between the classical and E1 Tor proteins. Genetic analysis of a range of classical and environmental isolates reveals strict conservation of the tcpA gene in all clinical isolates examined, and shows the O139 (Bengal) pilin to be of E1 Tor type. TcpA -related fragments of various sizes were detected in the genomes of environmental Vibrio chohrae isolates by Southern hybridisation. Five environmental Vibrio cholerae isolates, 2 non-cholera vibrios, and an Escherichia coli strain, as well as 18 clinical O1 and O139 isolates, were tested by polymerase chain reaction (PCR) at high and low stringencies. This readily identified clinical isolates, and O139 and E1 Tor products are easily separated from those of classical isolates by restriction fragment length poly-morphtem. The data presented illustrates the use of PCR to simply distinguish environmental isolates of O1 and non-O1 from the clinical O1 and O139 isolates tested, and for differentiating classical from E1 Tor (and O139) isolates. This information also supports the notion that only two TcpA types are needed in vaccines targeting O1 and O139 (Bengal) cholera strains, and demonstrates the antigenic stability of this important surface-presented epitope over time.