Genetic Diversity and Population Structure of Vibrio cholerae

Abstract

Multilocus enzyme electrophoresis (MLEE) of 397 Vibrio cholerae isolates, including 143 serogroup reference strains and 244 strains from Mexico and Guatemala, identified 279 electrophoretic types (ETs) distributed in two major divisions (I and II). Linkage disequilibrium was demonstrated in both divisions and in subdivision Ic of division I but not in subdivision Ia, which includes 76% of the ETs. Despite this evidence of relatively frequent recombination, clonal lineages may persist for periods of time measured in at least decades. In addition to the pandemic clones of serogroups O1 and O139, which form a tight cluster of four ETs in subdivision Ia, MLEE analysis identified numerous apparent clonal lineages of non-O1 strains with intercontinental distributions. A clone of serogroup O37 that demonstrated epidemic potential in the 1960s is closely related to the pandemic O1/O139 clones, but the nontoxigenic O1 Inaba El Tor reference strain is not. A strain of serogroup O22, which has been identified as the most likely donor of exogenous rfb region DNA to the O1 progenitor of the O139 clone, is distantly related to the O1/O139 clones. The close evolutionary relationships of the O1, O139, and O37 epidemic clones indicates that new cholera clones are likely to arise by the modification of a lineage that is already epidemic or is closely related to such a clone.

Vibrio cholerae O37: one of the exceptions that prove the rule

“…This is fully consistent with the studies discussed previously in this article, which report V. cholerae O37 that are non-toxigenic and distantly related to V52, ATCC 25872, or other related isolates (e.g. [25,35]). There have been recent clinical reports of infection caused by non-toxigenic V. cholerae O37 that do not harbour VPI-I, but are cytotoxic in in vitro models [55].…”

“…This, together with the finding in 1999 that a non-toxigenic V. cholerae O37 from Guatemala was closely related to O37 lineage isolates [25], strongly suggests that this O37 lineage is globally distributed.…”

“…Surprisingly, they also found that a non-O1/O139 environmental isolate M1618 (also named N1 and V523; Table 1) obtained in Australia during 1977 was identical to the Sudan clone, and was both toxigenic and harboured VPI-I [50]. This, together with the finding in 1999 that a non-toxigenic V. cholerae O37 from Guatemala was closely related to O37 lineage isolates [25], strongly suggests that this O37 lineage is globally distributed.…”

Integrated view of Vibrio cholerae in the Americas

“…A recent study in Thailand, however, recovered Classical strains isolated as late as 2000 (22), indicating that this lineage persisted longer than previously thought. It has been proposed that Classical cholera isolates were present in Mexico more than a decade earlier and persisted there until the mid-1990s (21) because of a single case, imported into the United States from Cancún, Mexico, in 1983 (23,24). This isolate was subsequently shown to be a member of the Gulf Coast lineage by ribotyping and electrophoretic typing (ET) (23)(24)(25).…”

“…It has been proposed that Classical cholera isolates were present in Mexico more than a decade earlier and persisted there until the mid-1990s (21) because of a single case, imported into the United States from Cancún, Mexico, in 1983 (23,24). This isolate was subsequently shown to be a member of the Gulf Coast lineage by ribotyping and electrophoretic typing (ET) (23)(24)(25). Our phylogenetic data show that Classical biotype isolates in Mexico in the mid-1990s are part of the Classical lineage, and not derived from the Gulf Coast lineage (Fig.…”