Second-line drug susceptibility testing of MDR and XDR Mycobacterium tuberculosis by the microplate colorimetric-based method and MGIT 960 system

IMPERIALE B; B DI GIULIO; MORCILLO N

Florida

Jornada; Jornadas Interdisciplinarias y actualización en Trasplante pulmonar en Fibrosis Quistica; 2010

Hospital Dr. Antonio A. Cetrángolo

Accurate treatments of tuberculosis (TB) cases due to multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis emphasizes the necessity of new tools for rapid detection of these strains in clinical laboratories. Minimal inhibitory concentrations (MICs) by MGIT960 and the microplate colorimetric-based method using MTT or resarzurin (CMM) were determined for the following drugs (µg/ml): amikacin (AMK): 2.0, 4.0, 8.0; kanamycin (KM), capreomycin (CPM), ethionamide (ETH): 2.5, 5.0, 10.0; cycloserine (CS): 15.0; ofloxacin (OFX) and linezolide (LZ): 0.5, 1.0, 2.0; and moxifloxacin (MOX) 0.25, 0.5, 1.0. MICs were performed on 94 clinical isolates. Inoculated MGITs were incubated in the instrument for no longer than 21 days. A strain was considered resistant if a positive signal flagged from the drug-containing tube within 3 days of the positive control tube. CMM plates were incubated for 8 days average. Statistical methods were applied to define drug-resistant strains on the basis of the comparison between results obtained by MGIT960 and CMM with the proportion method (gold standard). Critical concentrations were identified (µg/ml): AMK: 4.0; CPM, ETH and KM: 5.0; CS: 30.0; LZ: 1.0; MOX: 0.5; OFX: 2.0. Accuracy of MGIT960 and CMM was 100% for AMK, CPM, OFX, MOX and LZ. Results were obtained in less than 10 days for both MGIT960 and CMM, which being an in house method, was cheaper but more laborious than MGIT960. Our results showed that both methods could be promissory implemented as rapid diagnosis tools to detect MDR and XDR-TB cases in clinical practice.