Multicenter study of MTT and resazurin assays for testing susceptibility to first-line anti-tuberculosis drugs.
OBJECTIVE
A multicentre evaluation was performed to assess two rapid low-cost methods, MTT (3-[4.5-dimethylthiazol-2-yl]-2.5-diphenyltetrazolium bromide) and resazurin assays, for testing the susceptibility of Mycobacterium tuberculosis to the first-line anti-tuberculosis drugs rifampicin (RMP), isoniazid (INH), ethambutol (EMB) and streptomycin (SM).


METHODS
Thirty coded M. tuberculosis strains were sent to seven laboratories located in Latin America, representing six countries. Each site performed the colorimetric assays, MTT and resazurin, blind for the first-line drugs RMP, INH, EMB and SM. The minimum inhibitory concentration results obtained were compared to the conventional proportion method on Lowenstein-Jensen medium.


RESULTS
After establishing the breakpoint concentrations, excellent results were obtained for RMP, INH and EMB, with levels of specificity and sensitivity of between 96% and 99%.


CONCLUSIONS
MTT and resazurin assays are promising, accessible new alternative methods for middle- and low-resource countries that need low-cost methods to perform rapid susceptibility testing of M. tuberculosis to key anti-tuberculosis drugs.
Martin
A
A
Mycobacteriology Unit, Institute of Tropical Medicine, Antwerp, Belgium. amartin@itg.be
Morcillo
N
N
Lemus
D
D
Montoro
E
E
Telles
M A da Silva
MA
Simboli
N
N
Pontino
M
M
Porras
T
T
León
C
C
Velasco
M
M
Chacon
L
L
Barrera
L
L
Ritacco
V
V
Portaels
F
F
Palomino
J C
JC
D000995:Antitubercular Agents / Q000494:pharmacology*; D004396:Coloring Agents; D024881:Drug Resistance, Bacterial; D006801:Humans; D007202:Indicators and Reagents; D007843:Latin America; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000472:pathogenicity; D010078:Oxazines; D012016:Reference Values; D015203:Reproducibility of Results; D013778:Tetrazolium Salts; D013844:Thiazoles; D014397:Tuberculosis, Pulmonary / Q000188:drug therapy; D014966:Xanthenes
D000995:Antitubercular Agents; D004396:Coloring Agents; D007202:Indicators and Reagents; D010078:Oxazines; D013778:Tetrazolium Salts; D013844:Thiazoles; D014966:Xanthenes; C005843:resazurin; C022616:thiazolyl blue