Correlating Minimum Inhibitory Concentrations of ofloxacin and moxifloxacin with gyrA mutations using the genotype MTBDRsl assay

Abstract

Objective To correlate gyrA mutations found on the Genotype MTBDRsl assay in Mycobacterium tuberculosis (MTB) isolates with Minimum Inhibitory Concentrations (MICs) to the fluoroquinolones compounds ofloxacin (OFX) and moxifloxacin (MXF). Methods MICs for OFX and MXF were ascertained for 93 archived clinical MTB isolates that showed gyrA mutations at Ala90Val, Ser91Pro, Asp94Ala, Asn/Tyr, Gly and His. Thirty fluoroquinolones susceptible isolates as determined by presence of all wild-type gyrA bands on the Genotype MTBDRsl assay were also included. Results gyrA mutations at Ala90Val (n=25), Ser91Pro (n=6), Asp94Ala (n=4), Asp94Asn/Tyr (n=13), Asp94Gly (n=42) and Asp94His (n=3) were observed. Isolates with mutations at Ala90Val or Ser91Pro had MIC90 of 4.0µg/ml and 1.0µg/ml for OFX and MXF, respectively, and isolates with mutations at Asp 94Ala, Asn/Tyr, Gly and His had MIC90 of 8.0µg/ml, and 2.5µg/ml for OFX and MXF, respectively. Conclusions MTB MICs were found to be consistently lower for MXF than for OFX among isolates with the same gyrA mutation (e.g. Ala90Val). The majority of MTB isolates containing mutations at Asp94Ala, Asn/Tyr, Gly and His in gyrA were associated with a moderate level of resistance to MXF (MIC=2.5µg/ml), although 3 isolates with the mutations Asp94Asn/Tyr/Gly were associated with a high level of resistance to both fluoroquinolones (MXF MICs = 5.0–8.0µg/ml, OFX MICs = ≥10.0µg/ml).

Determination of MICs of levofloxacin for <I>Mycobacterium tuberculosis</I> with <I>gyr</I>A mutations

“…Judged by MIC90, mutations at Asp94Asn/Tyr, Gly or His were linked to a higher level of resistance to LVX compared to mutations at Ala90Val, Ser91Pro or Asp94Ala. These results were similar to those MIC levels previously reported for these isolates against other FQ compounds, 7 suggesting that clinical MTB isolates with gyrA mutations in the 90 and 91 codons have the potential to be treated with standard or increased LVX dosing. Small differences discovered between the different FQ MIC findings, meanwhile, may have significant clinical implications in deciding how, and with what FQ compounds, to best treat different infections.…”

“…5 In order to build upon our knowledge of the fluoroquinolone compounds available for TB treatment, we performed LVX Minimum Inhibitory Concentrations (MICs) for 123 Mycobacterium tuberculosis ( MTB ) isolates that were characterized in our earlier study. 7 We correlated LVX MICs with specific gyrA mutations found via the Genotype MTBDR sl assay to determine whether these commonly occurring mutations were associated with different levels of LVX resistance.…”

Evaluation of the GenoType MTBDR sl Version 2.0 Assay for Second-Line Drug Resistance Detection of Mycobacterium tuberculosis Isolates in South Africa

“…Furthermore, gyrA mutations D94G and D94N were observed in the majority of the isolates tested. Previous studies have indicated that isolates harboring these mutations exhibit high levels of resistance to FLQ (15,16). The gyrA MUT3D/D94H mutation, reported as a rare in silico mutant (13,17), was observed in 9/85 (10.6%) of mutations identified from these clinical isolates.…”

Evaluation of a Rapid Molecular Drug-Susceptibility Test for Tuberculosis

“…This situation was almost always associated with gyrA A90V or S91P mutations, which confer low-level moxifloxacin resistance, with minimum inhibitory concentrations (MICs) of 0.25 to 1.0 μ g per milliliter. 16,32 Although these MICs are higher than those of wild-type M. tuberculosis , isolates with gyrA A90V or S91P mutations are potentially treatable with increased moxifloxacin dosing, 33,34 and these mutations can be distinguished from other gyrA mutations with the use of the investigational assay. 11 Heteroresistance was detected by the investigational assay in some phenotypically susceptible isolates.…”