Wild-Type MIC Distributions for Aminoglycoside and Cyclic Polypeptide Antibiotics Used for Treatment of Mycobacterium tuberculosis Infections

Abstract

The aminoglycosides and cyclic polypeptides are essential drugs in the treatment of multidrug-resistant tuberculosis, underscoring the need for accurate and reproducible drug susceptibility testing (DST). The epidemiological cutoff value (ECOFF) separating wild-type susceptible strains from non-wild-type strains is an important but rarely used tool for indicating susceptibility breakpoints against Mycobacterium tuberculosis. In this study, we established wild-type MIC distributions on Middlebrook 7H10 medium for amikacin, kanamycin, streptomycin, capreomycin, and viomycin using 90 consecutive clinical isolates and 21 resistant strains. Overall, the MIC variation between and within runs did not exceed ؎1 MIC dilution step, and validation of MIC values in Bactec 960 MGIT demonstrated good agreement. Tentative ECOFFs defining the wild type were established for all investigated drugs, including amikacin and viomycin, which currently lack susceptibility breakpoints for 7H10. Five out of seven amikacin-and kanamycin-resistant isolates were classified as susceptible to capreomycin according to the current critical concentration (10 mg/liter) but were non-wild type according to the ECOFF (4 mg/liter), suggesting that the critical concentration may be too high. All amikacinand kanamycin-resistant isolates were clearly below the ECOFF for viomycin, and two of them were below the ECOFF for streptomycin, indicating that these two drugs may be considered for treatment of amikacinresistant strains. Pharmacodynamic indices (peak serum concentration [C max ]/MIC) were more favorable for amikacin and viomycin compared to kanamycin and capreomycin. In conclusion, our data emphasize the importance of establishing wild-type MIC distributions for improving the quality of drug susceptibility testing against Mycobacterium tuberculosis.

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

“…The critical concentrations on 7H10 for KAN, AMK, and CAP were 5.0, 4.0, and 4.0 mg/liter, respectively (33). The MICs of H37Rv ATCC 27294 were 1 mg/liter for each drug, concordant with data from Juréen et al (41). c Resistance-associated genes of isolates cultured in tubes with antibiotics were sequenced.…”

Predicting Extensively Drug-Resistant Mycobacterium tuberculosis Phenotypes with Genetic Mutations

“…One possible explanation for the observed lack of specificity for predicting phenotypic CAP resistance may lie in the WHO-recommended critical concentration for MGIT 960 DST that we used for our study. Since the current critical concentration was accepted by the WHO, it has been demonstrated that this critical concentration is substantially higher than the epidemiological cutoff (ECOFF) that separates wild-type M. tuberculosis from those with mutations conferring CAP resistance, which might result in non-wild-type isolates being classified as CAP s (38,39). Interpreted in the context of our findings, it is possible that the WHO-recommended critical concentration we used misclassified CAP-resistant organisms as susceptible, resulting in a reduced specificity of the mutation for predicting phenotypic resistance.…”

A Multilaboratory, Multicountry Study To Determine MIC Quality Control Ranges for Phenotypic Drug Susceptibility Testing of Selected First-Line Antituberculosis Drugs, Second-Line Injectables, Fluoroquinolones, Clofazimine, and Linezolid

“…However, similar MIC distributions have been reported for the same reference strain between different liquid culture systems, with MIC variability of a 2-fold dilution or less (5). Studies using 7H10 agar or Bactec MGIT 960 and Bactec 460 determined MICs against H37Rv of 0.5 g/ml for ofloxacin, 0.125 g/ml for moxifloxacin, 0.25 g/ml for levofloxacin, 2 g/ml for ethambutol, 0.5 g/ml for amikacin, and 1 to 2 g/ml for both kanamycin and capreomycin (14)(15)(16); all of these values lie within the MIC QC ranges we report for these drugs. For isoniazid, a microdilution method using 7H10 agar or Bactec 460 yielded a MIC range of 0.064 to 0.125 g/ml for H37Rv, which is essentially within the MIC QC range of 0.03 to 0.12 g/ml determined in this study (16).…”