Evaluation of Mycobacterium tuberculosis typing methods in a 4-year study in Schleswig-Holstein, Northern Germany

In order to evaluate the discriminatory power of different methods for genotyping of Mycobacterium tuberculosis complex (MTBC) isolates, we compared the performance of (i) IS6110 DNA fingerprint typing, (ii) spoligotyping, and (iii) 24-loci mycobacterial interspersed repetitive units-variable number of tandem repeats (MIRU-VNTR) typing in a long-term study on the epidemiology of tuberculosis (TB) in Schleswig-Holstein, the northernmost federal state of Germany. In total, we analyzed 277 MTBC isolates collected from patients between the years 2006 and 2010. The collection comprised a broad spectrum of 13 different genotypes, among which strains of the Haarlem genotype (31%) were most prominent, followed by strains belonging to the Delhi and Beijing lineages (7% and 6%, respectively). On the basis of IS6110 restriction fragment length polymorphism (RFLP) and spoligotyping analyses, 211 isolates had unique patterns (76%) and 66 isolates (24%) were in 20 clusters. MIRU-VNTR combined with spoligotyping analyses revealed 202 isolates with unique patterns (73%) and 75 isolates in 18 clusters (27%). Overall, there was 93.1% concordance between the typing results obtained; 198 strains were identified as unique, and 60 isolates were clustered by both typing combinations (including all 31 isolates with confirmed epidemiological links). Of the remaining 19 isolates with discrepant results, 15 were falsely clustered by MIRU-VNTR (six Beijing genotype strains) and four were clustered by IS6110 RFLP (low IS6110 copy number) only. In conclusion, in the study population investigated, a minority of isolates, especially of the Beijing genotype, clustered by standard 24-loci MIRU-VNTR and without an obvious epidemiological link may require second-line typing by IS6110 RFLP or hypervariable MIRU-VNTR loci.