Molecular fingerprinting of Mycobacterium tuberculosis strains isolated in Vietnam using IS6110 as probe.

SETTING

Northern and Southern areas of Vietnam.

OBJECTIVE

To study the correlation between DNA fingerprinting of 168 Mycobacterium tuberculosis strains isolated from patients with a particular historical past (political separation of Vietnam for 20 years) and data about geographical origin, drug susceptibility, HIV infection and BCG vaccination status.

METHODS

Comparison of restriction fragment length polymorphism (RFLP) patterns produced by Southern hybridization of Pvull-digested chromosomal DNA.

RESULTS

The number of IS6110 copies for the 168 strains ranges from 0 to 23. Strains originating from the North or the South differ strongly with respect to the number of copies of IS6110. Indeed, the strains originating from the north have predominantly from 3 to 14 IS6110 copies while the southern strains have predominantly from 15 to 23 IS6110 copies. Furthermore, strains isolated in the North are dispersed into 6 groups whereas 80% of the strains isolated in the South form a single group. Moreover, the prevalence of drug resistance is higher in strains isolated in the South than in the North. No noticeable correlation is observed between RFLP patterns, drug susceptibility, or HIV infection.

CONCLUSION

The IS6110 fingerprints of 168 M. tuberculosis strains isolated in Vietnam showed a high range of polymorphism. Only a few strains have been found with no IS6110 (1.8%). The differences between the strains from the North and South, having more than six IS6110, suggests that they derived from ancestral strains that would be distinguishable by the number of IS6110 and their transposition sites throughout the genome. The genomic structure of the population of strains from South Vietnam resembles that of the Beijing strain population. This could account for a similar evolution of M. tuberculosis due to a selection by BCG-induced immunity in the two populations.