Mutations in therrsA1401G Gene and Phenotypic Resistance to Amikacin and Capreomycin inMycobacterium tuberculosis

Abstract

The aminoglycosides amikacin (AMK)/kanamycin (KAN) and the cyclic polypeptide capreomycin (CAP) are important injectable drugs in the treatment of multidrug-resistant tuberculosis. Cross-resistance among these drug classes occurs and information on the minimum inhibitory concentrations (MICs), above the normal wild-type distribution, may be useful in identifying isolates that are still accessible to drug treatment. Isolates from the Eastern Cape Province of South Africa were subjected to DNA sequencing of the rrs (1400-1500 region) and tlyA genes. Sequencing data were compared with (i) conventional susceptibility testing at standard critical concentrations (CCs) on Middlebrook 7H11 agar and (ii) MGIT 960-based MIC determinations to assess the presence of AMK- and CAP-resistant mutants. Isolates with an rrs A1401G mutation showed high-level resistance to AMK (>20 mg/L) and decreased phenotypic susceptibility to CAP (MICs 10-15 mg/L). The MICs of CAP were below the bioavailability of the drug, which suggests that it may still be effective against multi- or extensively drug resistant tuberculosis [M(X)DR-TB]. Agar-based CC testing was found to be unreliable for resistance recognition of CAP in particular.

Genotypic Susceptibility Testing of Mycobacterium tuberculosis Isolates for Amikacin and Kanamycin Resistance by Use of a Rapid Sloppy Molecular Beacon-Based Assay Identifies More Cases of Low-Level Drug Resistance than Phenotypic Lowenstein-Jensen Testing

“…These results suggest that the MGIT or MycoTB method should be preferred for testing phenotypic resistance to KAN. They also highlight the power of genotypic resistance tests, such as ours, to detect mutations which cause low-level resistance and may be missed by phenotypic tests alone (30,31,36).…”

Evaluation of Pyrosequencing for Detecting Extensively Drug-Resistant Mycobacterium tuberculosis among Clinical Isolates from Four High-Burden Countries

“…It is therefore possible that the WHOrecommended critical concentration that we used here resulted in the misclassification of CAP-resistant organisms as "susceptible" when, in fact, they contained the 1401 A-G mutation in the rrs, ultimately resulting in the reduced specificity of PSQ for predicting phenotypic CAP resistance. In addition, as discussed in Sirgel et al (40), clinical isolates from South Africa with the 1401 A-G mutation in the rrs gene showed decreased phenotypic susceptibility to CAP. Furthermore, while the rrs 1401 A-G mutation is implicated in cross-resistance to all three injectable drugs, some studies have shown that mutations outside our considered genomic regions, most notably mutations in eis promoter and tlyA, may independently confer resistance to KAN and CAP, respectively (41)(42)(43)(44).…”

Molecular Investigation of Resistance to Second-Line Injectable Drugs in Multidrug-Resistant Clinical Isolates of Mycobacterium tuberculosi s in France

“…Finally, no mutation in tlyA was observed in any of our isolates, so tlyA does not seem to be implicated in CAP resistance in our MDR clinical isolates. Mutations in the tlyA gene associated with CAP resistance were reported to be rare in the surveyed literature (found in ϳ0 to 3% of resistant strains), and their implication in resistance has not been undoubtedly established (4,7,8,10,11,14,(22)(23)(24)(25)(26)(27).…”