Stability of IS6110 restriction fragment length polymorphism patterns of Mycobacterium tuberculosis strains in actual chains of transmission.

The stability of IS6110 restriction fragment length polymorphism (RFLP) patterns of Mycobacterium tuberculosis strains in actual transmission chains has been assessed by analyzing the variability of IS6110 RFLP patterns of strains in fingerprint clusters that have been confirmed by classical epidemiological data. Forty susceptible and 35 drug-resistant (including 17 multidrug-resistant) M. tuberculosis strains obtained from 75 patients living in Germany have been analyzed. The epidemiological relationship among strains within the fingerprint clusters has been verified by family contacts (14 clusters) or by contact tracing of the public health offices (7 clusters). The time spans between the first and the last isolate of one cluster ranged from less than 1 to 29 months. Of the 75 strains only 1 showed a one-band variation when compared to the other nine isolates grouped in the same cluster, corresponding with a rate of change of approximately 1.9% per possible transmission (one index patient per cluster was subtracted from the total number of isolates). These results confirm a high degree of stability of IS6110 RFLP patterns of transmitted M. tuberculosis strains. Furthermore, the data presented indicate that isolates with identical IS6110 DNA fingerprint patterns are a good indicator for the rate of recent transmission in a study population.