title: Impact of Fgd1 and ddn diversity in Mycobacterium tuberculosis complex on in vitro susceptibility to PA-824.
abstract: PA-824 is a promising drug candidate for the treatment of tuberculosis (TB). It is in phase II clinical trials as part of the first newly designed regimen containing multiple novel antituberculosis drugs (PA-824 in combination with moxifloxacin and pyrazinamide). However, given that the genes involved in resistance against PA-824 are not fully conserved in the Mycobacterium tuberculosis complex (MTBC), this regimen might not be equally effective against different MTBC genotypes. To investigate this question, we sequenced two PA-824 resistance genes (fgd1 [Rv0407] and ddn [Rv3547]) in 65 MTBC strains representing major phylogenetic lineages. The MICs of representative strains were determined using the modified proportion method in the Bactec MGIT 960 system. Our analysis revealed single-nucleotide polymorphisms in both genes that were specific either for several genotypes or for individual strains, yet none of these mutations significantly affected the PA-824 MICs (≤ 0.25 μg/ml). These results were supported by in silico modeling of the mutations identified in Fgd1. In contrast, "Mycobacterium canettii" strains displayed a higher MIC of 8 μg/ml. In conclusion, we found a large genetic diversity in PA-824 resistance genes that did not lead to elevated PA-824 MICs. In contrast, M. canettii strains had MICs that were above the plasma concentrations of PA-824 documented so far in clinical trials. As M. canettii is also intrinsically resistant against pyrazinamide, new regimens containing PA-824 and pyrazinamide might not be effective in treating M. canettii infections. This finding has implications for the design of multiple ongoing clinical trials.
authors.affiliation: Molecular Mycobacteriology, Research Center Borstel, Parkallee 18, 23845 Borstel, Germany.
authors.forename: Silke
authors.initials: S
authors.lastname: Feuerriegel
authors.forename: Claudio U
authors.initials: CU
authors.lastname: Köser
authors.forename: Davide
authors.initials: D
authors.lastname: Baù
authors.forename: Sabine
authors.initials: S
authors.lastname: Rüsch-Gerdes
authors.forename: David K
authors.initials: DK
authors.lastname: Summers
authors.forename: John A C
authors.initials: JA
authors.lastname: Archer
authors.forename: Marc A
authors.initials: MA
authors.lastname: Marti-Renom
authors.forename: Stefan
authors.initials: S
authors.lastname: Niemann
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics*; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D014644:Genetic Variation; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000592:standards; D009169:Mycobacterium tuberculosis / Q000145:classification / Q000187:drug effects* / Q000235:genetics; D009593:Nitroimidazoles / Q000494:pharmacology*; D020641:Polymorphism, Single Nucleotide; D017422:Sequence Analysis, DNA
chemical_list: D000995:Antitubercular Agents; D001426:Bacterial Proteins; D009593:Nitroimidazoles; C410767:pretomanid