Simultaneous infection with multiple strains of Mycobacterium tuberculosis identified by restriction fragment length polymorphism analysis.

Simultaneous infection with multiple strains of Mycobacterium tuberculosis was confirmed in two isolates of a total of 543 culture-positive tuberculosis patients from the Model DOTS area of Thiruvallur, South India, using IS6110 and direct repeat restriction fragment length polymorphism (DR-RFLP). The two isolates showing different intensities of IS6110 band patterns were further analysed by repeating RFLP on their alternate cultures and individual colonies. The results showed respectively two and three distinct IS6110 RFLP patterns, indicating mixed infection. The possibility of cross contamination at laboratory or DNA level was ruled out. Additional DR-RFLP also confirmed infection with multiple strains. This study found evidence of co-infection with two or three different strains of M. tuberculosis, showing distinct RFLP patterns.