Relatedness of Vibrio cholerae O1/O139 isolates from patients and their household contacts, determined by multilocus variable-number tandem-repeat analysis

Abstract

The genetic relatedness of Vibrio cholerae O1/O139 isolates obtained from 100 patients and 146 of their household contacts in Dhaka, Bangladesh, between 2002 and 2005 was assessed by multilocus variable-number tandem-repeat analysis. Isolate genotypes were analyzed at five loci containing tandem repeats. Across the population, as well as within households, isolates with identical genotypes were clustered in time. Isolates from individuals within the same household were more likely to have similar or identical genotypes than were isolates from different households, but even within a household, isolates from different individuals often had different genotypes. When household contacts were sampled regularly for 3 weeks after the illness of the household index patient, isolates with genotypes related to the index patient appeared in contacts, on average, approximately 3 days after the index patient, while isolates with unrelated genotypes appeared in contacts approximately 6 days after. Limited data revealed that multiple isolates from the same individual collected within days of each other or even from a single stool sample may have identical, similar, or unrelated genotypes as well. Our results demonstrate that genetically related V. cholerae strains cluster in local outbreaks but also suggest that multiple distinct strains of V. cholerae O1 may circulate simultaneously within a household.

FIG. 1.

The three largest clonal complexes from eBURST analysis. Each line between genotypes represents a change in a single locus.

FIG. 2.

Variations over time in the relatedness, by various criteria, of paired V. cholerae isolates from distinct Dhaka households.

FIG. 3.

(A) MLVA genotypes of V. cholerae isolates collected from three households in February and March 2004. The genotype of each isolate is displayed as a five-digit number; identical genotypes have the same background and surrounding line. All of the isolates illustrated belong to serogroup O1 serotype Inaba. (B) PFGE gel of NotI-digested DNA from the same isolates displayed in panel A. The variable bands are indicated by arrows, and each lane is identified by the MLVA genotype and the source household, individual, and day.

FIG. 4.

Proportions of genetic variants among colonies selected at the same time from a single stool sample. Each pie diagram indicates a separate stool sample; each sector is in proportion to the frequency with which the type of genetic variant was found.