Laboratory system to detect multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis strains in clinical practice

NORA MORCILLO; BELÉN IMPERIALE; BEATRIZ DI GIULIO

Berlin

Congreso; 18 Congreso Anual de la Sociedad Europea de Medicina Respiratoria (ERS); 2008

Sociedad Europea de Medicina Respiratoria (ERS)

Multidrug-resistant (MDR-TB) and the recently described extensively drug-resistant tuberculosis (XDR-TB) are emergent health problems frequently associated to HIV co-infection. Colorimetric microplate-based method using MTT (M-MTT) has been implemented in the laboratory to routinely assess the susceptibility of the strains to first and second-line drugs. In current practice and in a first step, minimal inhibitory concentration (MIC) of isoniazid (INH), rifampicin (RIF), streptomycin (SM), ethambutol (EMB) and levofloxacin (LX) are determined on clinical isolates. After detecting MDR, second-line drugs are tested: amikacin (AMK), capreomycin (CPM), cycloserine (CS), ethionamide (ETH), kanamycin (KM),  linezolide (LZ), moxifloxacin (MOX), rifabutin (RBT) and p-aminosalycilic acid (PAS). The gold standards for first-line drugs are the proportion method (PM) on Lowenstein-Jensen and SIRE MGIT960®. For second-line drugs it is the PM on Middlebrook 7H11. In this work we performed drug-susceptibility testing on 1429 clinical isolates obtained from 1340 cases (2004-2007). The tested drug range-concentrations (mg/L) were: INH, RBT: 1.00 to 0.03; RIF: 2.00 to 0.06; LX, LZ, MOX: 4.00 to 0.13; AMK, CPM, EMB, ETH, KM, PAS: 8.00 to 0.25; CS: 120.00 to 3.75. A total of 70 (5.2%) resistant cases, 61 MDR-TB and 9 XDR-TB, were diagnosed between 8 to 16 days. This system could become part of an algorithm designed to detect MDR-TB and XDR-TB strains by a rapid and low cost technology in reference laboratories.