[IS6110 for typing strains of Mycobacterium tuberculosis: application of a standardized protocol with computerized...

For the epidemiological control of tuberculosis it is necessary to use specific markers for strain differentiation. The analysis of the restriction fragment length polymorphism (RFLP) by using the insertion sequence IS6110 as a probe, allows us to establish accurately the strains which are around in a population. Our study evaluates the efficiency of this marker in 136 strains of Mycobacterium tuberculosis isolated from our surroundings. A standardized protocol is used, and a computerized system to analyze the images is described.

DNA restriction was done with PvuII. The filters were revealed by following a chemiluminescence method using a 867 bp probe, which is located to the right of the PvuII site IS6110. The comparison of the patterns obtained was done in a computer. The coefficient of Dice was calculated to express the similarity of the profiles given by two strains. The strains were clustered by the UPGMA method. The graphic representation of the clusters was done by means of homology dendrograms.

124 different patterns were obtained from which 118 strains had a unique pattern while 18 shared it. The index of discrimination was 0.996. Ninety two percent of the strains had more than 6 bands and none had no IS6110. The median of homology was 27% in 8 of the patients, 2 consecutive isolates were studied with the result of no variation seen on the patterns.

IS6110 has shown very effective because of its stability and high discriminative power. The standardized protocol together with a computerized analysis of the images obtained allows comparison of results, furthermore, to establish centralized data base. This would be very useful for epidemiological studies of tuberculosis and the chase of strains with special characteristics.