On the possibility of cross-resistance between rifampicin and clofazimine in mycobacteria--a laboratory study.

One-way cross-resistance to rifampicin in clofazimine-resistant substrains of Mycobacterium smegmatis ATCC 607 was seen in 4 instances, whereas at most a borderline situation (probably within the experimental error) occurred in this respect with Mycobacterium parafortuitum 16009 and with strains of Mycobacterium "lufu" and Mycobacterium fortuitum. Clofazimine-resistant sub-strains were not isolated from the parental strains of Mycobacterium tuberculosis. Methodological influences (the gradient plate technique was used in this study) are discussed.