RpoB polymorphisms in Mycobacterium tuberculosis complex from a population in Guinea-Bissau

Abstract

The global tuberculosis (TB) threat is diffi cult to evaluate in countries with scarce laboratory facilities where little is known about the genetic basis of drug resistance, including the rpoB RRDR (rifampicin resistance determining region) of the Mycobacterium tuberculosis complex (MTC). The present study aimed at performing a preliminary evaluation of rpoB polymorphisms in a DNA set of MTC isolates from Guinea-Bissau patients. Ninety-four sputum specimens (74 bleach processed and 20 unprocessed) were sent to Lisbon for molecular analysis (n=94) and drug susceptibility testing (n=20). A 369bp region of the rpoB gene (including the 81bp RRDR), was amplifi ed. Sequencing was used as the gold standard for the identifi cation of point mutations. Two polymorphisms were identifi ed: The alteration S531L, present in 3.2% of the specimens, and a new mutation, present in 28.7%, corresponding to nucleotide and amino acid polymorphism C224T and S469L, respectively, detected upstream from the RRDR, and not associated with RMP resistance. An NCBI BLAST revealed M. tuberculosis K85 (M. africanum) as the only strain presenting this polymorphism. The circulation of S531L mutated stains, associated with RMP resistance, points to the urgent need to further investigate RMP resistance in this African region. Moreover, the strains presenting the S469L polymorphism showed no other mutations suggesting that its role on MP´susceptibility/ resistance or in providing a genetic background for the occurrence of RMP resistance associated mutations should be further investigated. Also, future genotyping studies could clarify whether this new mutation is a genetic signature of some M. africanum strains.