The insertion sequence IS 6110 was used to differentiate clinical Moroccan isolates of Mycobacterium tuberculosis by using two non radioactive probes. Among 16 strains isolated from patients clinically related, 10 had similar IS 6110 restriction fragment length polymorphism (RFLP) patterns, confirming that they were derived from a common source. Two strains were isolated from the same patient (sputum, lymph node) showed identical profiles hybridized with IS 6110 element. Four sequential strains isolated from the same patients before treatment and after one year had identical IS 6110 RFLP patterns suggesting relapse and not reinfection. Twenty-one strains with identical drug susceptibility showed different IS 6110 RFLP profiles confirming no correlation between antibiotic resistance profiles and IS 6110 RFLP patterns. Since RFLP analysis by using IS 6110 element is a useful tool for the epidemiological survey, of tuberculosis.
