Molecular characterisation of rifampicin-resistant strains from Malawi.

BACKGROUND

Availability and access to the detection of resistance to anti-tuberculosis drugs remains a significant challenge in Malawi due to limited diagnostic services. The Xpert MTB/RIF can detect and resistance to rifampicin in a single, rapid assay. Rifampicin-resistant has not been well studied in Malawi.

OBJECTIVES

We aimed to determine mutations in the rifampicin resistance determining region (RRDR) of the B gene of strains which were defined as resistant to rifampicin by the Xpert MTB/RIF assay.

METHODS

Rifampicin-resistant isolates from 43 adult patients (≥ 18 years) from various districts of Malawi were characterised for mutations in the RRDR (codons 507-533) of the B gene by DNA sequencing.

RESULTS

Mutations were found in 37/43 (86%) of the resistant isolates in codons 511, 512, 513, 516, 522, 526 and 531. The most common mutations were in codons 526 (38%), 531 (29.7%) and 516 (16.2%). Mutations were not found in 6/43 (14%) of the resistant isolates. No novel B mutations other than those previously described were found among the rifampicin-resistant complex strains.

CONCLUSION

This study is the first to characterise rifampicin resistance in Malawi. The chain-termination DNA sequencing employed in this study is a standard method for the determination of nucleotide sequences and can be used to confirm rifampicin resistance obtained using other assays, including the Xpert MTB/RIF. Further molecular cluster analysis, such as spoligotyping and DNA finger printing, is still required to determine transmission dynamics and the epidemiological link of the mutated strains.