Intrinsic rifamycin resistance of Mycobacterium abscessus is mediated by ADP-ribosyltransferase MAB_0591

<span class="paragraphSection"><strong>Objectives:</strong> Rifampicin, a potent first-line TB drug of the rifamycin group, shows only little activity against the emerging pathogen <span style="font-style:italic;">Mycobacterium abscessus.</span> Reportedly, bacterial resistance to rifampicin is associated with polymorphisms in the target gene <span style="font-style:italic;">rpoB</span> or the presence of enzymes that modify and thereby inactivate rifampicin. The aim of this study was to investigate the role of the <span style="font-style:italic;">MAB_0591</span> (<span style="font-style:italic;">arrMab</span>)-encoded rifampicin ADP-ribosyltransferase (Arr_<span style="font-style:italic;">Mab</span>) in innate high-level rifampicin resistance in <span style="font-style:italic;">M. abscessus.</span><strong>Methods:</strong> Recombinant <span style="font-style:italic;">Escherichia coli</span> and <span style="font-style:italic;">Mycobacterium tuberculosis</span> strains expressing <span style="font-style:italic;">MAB_0591</span> were generated, as was an <span style="font-style:italic;">M. abscessus</span> deletion mutant deficient for <span style="font-style:italic;">MAB_0591.</span> MIC assays were used to study susceptibility to rifampicin and C25 carbamate-modified rifamycin derivatives.<strong>Results:</strong> Heterologous expression of <span style="font-style:italic;">MAB_0591</span> conferred rifampicin resistance to <span style="font-style:italic;">E. coli</span> and <span style="font-style:italic;">M. tuberculosis</span>. Rifamycin MIC values were consistently lower for the <span style="font-style:italic;">M. abscessus</span> Δ<span style="font-style:italic;">arrMab</span> mutant as compared with the <span style="font-style:italic;">M. abscessus</span> ATCC 19977 parental type strain. The rifamycin WT phenotype was restored after complementation of the <span style="font-style:italic;">M. abscessus</span> Δ<span style="font-style:italic;">arrMab</span> mutant with <span style="font-style:italic;">arrMab</span>. Further MIC data demonstrated that a C25 modification increases rifamycin activity in WT <span style="font-style:italic;">M. abscessus</span>. However, MIC studies in the <span style="font-style:italic;">M. abscessus</span> Δ<span style="font-style:italic;">arrMab</span> mutant suggest that C25 modified rifamycins are still subject to modification by Arr_<span style="font-style:italic;">Mab</span>.<strong>Conclusions:</strong> Our findings identify Arr_<span style="font-style:italic;">Mab</span> as the major innate rifamycin resistance determinant of <span style="font-style:italic;">M. abscessus.</span> Our data also indicate that Arr_<span style="font-style:italic;">Mab</span>-mediated rifamycin resistance in <span style="font-style:italic;">M. abscessus</span> can only in part be overcome by C25 carbamate modification.</span>

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