High strain diversity among isoniazid-resistant M tuberculosis isolates from the Free State and Northern Cape provinces

This study set out to determine the diversity of the isoniazid-resistant M tuberculosis isolates causing pulmonary tuberculosis in the Free State and Northern Cape provinces of South Africa. Thirty-seven isoniazid-resistant isolates from a nation-wide survey could be fingerprinted by IS6110-based RFLP. Spoligotyping and MIRU-VNTR typing were performed to confirm inconclusive results. The number of IS6110 copies per isolate varied from 2 to 18, with nine (24.3%) isolates harbouring five insertions or fewer. Nine (24.3%) of 37 cases grouped into four RFLP-clusters. The clustered isolates with fewer than five IS6110 copies were all shown to be different when   subjected to spoligotyping and MIRU-VNTR typing, whereas the clustering of the high-copy isolates was confirmed. The high degree of diversity among H-resistant isolates in the Free State suggests a low recent transmission rate, but this should be investigated by long-term analyses. For the Northern Cape province, representative sampling is needed before proper conclusions can be drawn