Usefulness of spoligotyping to discriminate IS6110 low-copy-number Mycobacterium tuberculosis complex strains cultured in Denmark

Mycobacterium tuberculosis complex strains cultured in Denmark have been an alyzed by IS6110 restriction fragment length polymorphism (RFLP) on a routi ne basis from 1992 and onwards, Due to the influx of immigrants with tuberc ulosis, the number of strains harboring only one to five copies of IS6110 h as increased steadily. Since the discriminatory power of IS6110 fingerprint ing for such strains is poor, we have performed additional genotyping of al l low-copy-number strains by the recently described PCR-based method known as spoligotyping, A total of 311 clinical strains were typed: 14 Mycobacter ium bovis BCG, 48 M. bovis, and 249 M. tuberculosis strains, Spoligotyping correctly differentiated M, bovis and M, bovis BCG from M, tuberculosis str ains, but it did not differentiate M. bovis from M, bovis BCG, All M. bovis BCG strains exhibited identical spoligotype patterns. The discriminatory p ower of spoligotyping of low-copy-number M. tuberculosis strains was higher than that of IS6110 fingerprinting, Based on RFLP typing solely, 83% of th e low-copy-number M. tuberculosis strains were found to form part of a clus ter, and 75% were found to form a cluster on the basis of spoligotyping, Wh en the two techniques were combined, the amount of clustering decreased to 55%, The combination of these two techniques might be valuable in studying the epidemiology of M, tuberculosis strains harboring few copies of the IS6 110 element.