Molecular Characterization ofVibrio choleraeO1 Biotype El Tor Strains Isolated between 1992 and 1995 in Calcutta, India: Evidence for the Emergence of a New Clone of the El Tor Biotype

Abstract

Sixty-one clinical strains of Vibrio cholerae O1 El Tor isolated in Calcutta before, during, and after the V. cholerae O139 Bengal outbreak were examined to see if the O1 strains of the post-O139 period were different from those in existence before. Comparison of the restriction fragment length polymorphism of the rRNA genes (ribotyping) and the CTX genetic element revealed that all "before" strains except 1 belonged to a single known ribotype, whereas all "after" strains except 2 belonged to a hitherto undescribed ribotype. Also, 23 of 25 "before" strains harbored two or more copies of CTX in tandem and also a "free" RS1 element away from CTX, whereas 19 of 21 "after" strains had a single copy of CTX and no free RS1 element. CTX occupied different chromosomal locations in "before" and "after" strains. These studies clearly showed that El Tor O1 strains, which displaced V. cholerae O139 in Calcutta, belonged to a new clone and suggested that there is a continuous genetic reassortment among El Tor strains of V. cholerae O1.

Vibrio cholerae O1 clinical strains isolated in 1992 in Kolkata with progenitor traits of the 2004 Mozambique variant

“…The analysis was extended further by generating ribotype profiles for these strains, a technique that has been used successfully to demonstrate the emergence and progression of different clones of V. cholerae strains that have been circulating in the Indian subcontinent over a period of time. It has already been reported that V. cholerae O1 strains that were isolated before the O139 outbreak in late 1992 had a typical BglI ribotype profile named RI (Sharma et al, 1997). The RII and RIII BglI ribotype profiles were assigned to V. cholerae O1 strains isolated during and after the O139 outbreaks.…”

“…4b, lane 1). The RI profile obtained with the 1992 Kolkata O1 strain had diverged from the profile obtained with O1 El Tor strains N16961 as well as reference O1 strain for RIII profile CO366 (Sharma et al, 1997). Apart from ribotyping, PFGE analysis is also a very useful technique to illustrate the clonal relatedness among different strains of the same species.…”

“…However, a resurgence of O1 vibrios occurred within a span of a year and both serogroups co-existed for a long period of time. Interestingly, the resurgent O1 vibrios in the post-O139 era were reported to belong to newer clones as compared to the pre-O139 era (Sharma et al, 1997 …”

Mortality, morbidity, and microbiology of endemic cholera among hospitalized patients in Dhaka, Bangladesh.

“…[48][49][50] Reasons for the disappearance of classical V. cholerae O1 and the sudden increases and decreases in cholera cases caused by specific El Tor Ogawa and Inaba V. cholerae O1 organisms are less well understood, but may relate to varying degrees of immunologic cross-protection, environmental ecology of organisms, or clonal selection. 8,48,[50][51][52][53][54][55] In conclusion, causative agents of cholera vary over time in an endemic setting, perhaps related to immunologic crossprotection, clonal selection, and/or environmental ecology of organisms. Additionally, death in hospitalized patients with cholera acquired in a modern endemic setting capable of appropriately managing fluid replacement therapy is most frequently due to concomitant infection, especially pneumonia.…”

Efficiency and specificity of CTXϕ chromosomal integration: dif makes all the difference

“…classical biotype isolates, which were the cause of earlier pandemics and are now extinct, the classical type phage CTXϕ CL is integrated on both chromosomes and never contains an RS1 element (16,17 Huber and Waldor (9) proposed that the integration of CTXϕ resulted from recombination between a 200-bp intergenic region (attP) of the replicative double-stranded form of CTXϕ and dif1 (attB) on chromosome I of V. cholerae (Fig. 1A).…”