Polymorphism in the curated library used for predicting multi-drug resistant TB (MDR-TB) and extensive-drug resistant TB (XDR-TB). (A) Polymorphisms associated with MDR-TB. (B) Polymorphisms associated with XDR-TB. Colour-coded bars in the Circos plot represent genes described to be involved in drug resistance (from Table 1). On top of each of these bars a grey histogram shows the mutation density (calculated as the number of polymorphic sites within windows of 20 bp) derived from the curated list of DR-associated mutations. These grey areas highlight the presence of DR-associated regions in candidate genes, which in some cases span the whole gene (for example, katG) or are confined to a certain region of the gene (for example, rpoB). Vertical black lines indicate the frequency of mutations (that is, the number of times the mutation has been observed) in phenotypically resistance isolates. Internal black lines show co-occurring mutations both within and between genes. The thickness of these lines is proportional to the frequency of the mutations appearing together.