L'antibiogramme sur MGIT (Mycobacterial Growth Indicator Tube) est compare a la methode des proportions en milieu solide pour l'etude de la sensibilite de Mycobacterium tuberculosis a l'isoniazide (INH), la rifampicine (RIF), la streptomycine (SM) et l'ethambutol (EMB). Cinquante-quatre souches de M. tuberculosis, dont 30 resistantes a au moins un des quatre antituberculeux cites, sont etudiees. Le MGIT est utilise selon les recommandations du fabricant : inoculum obtenu a partir de culture sur Lowenstein-Jensen ; concentrations testees pour INH, RIF, SM et EMB respectivement de 0,1 - 1 - 0,8 et 3,5 μg/ml ; lecture quotidienne du 3 e au 14 e jour en lumiere UV a 365 nm ; sensibilite definie par l'absence de croissance au plus 48 heures apres la positivite du tube temoin. Les tests discordants sont repetes.Le delai moyen du resultat est de 7,9 jours pour l'ensemble des antibiotiques. La contamination est de 0,4 %. La concordance entre les deux techniques est totale pour 48 souches (89 %). La concordance est de 100 % pour INH (23 resistantes (R)/31 sensibles [S]) et RIF (3R/51S). Pour SM elle est de 92,6 % (17R/33S), mais quatre isolats resistants en methode des proportions sont sensibles en MGIT. Pour trois de ces souches, on detecte une croissance 24 a 48 heures apres la limite fixee par le fabricant. Pour EMB la concordance est de 94,4 % (3R/48S), mais trois isolats resistants en methode des proportions sont sensibles en MGIT. L'antibiogramme sur MGIT, rapide et concordant avec la methode de reference, est un complement pour l'etude de la sensibilite a INH et RIF. Pour l'etude de EMB et SM, les limites decrites ne sont pas confirmees par les evaluations recentes. Le pyrazinamide ne peut etre etudie actuellement. La sensibilite aux contaminations bacteriennes limite l'usage du MGIT aux laboratoires specialises.
The reliability of mycobacterial growth indicator tube (MGIT) for testing susceptibility of Mycobacterium tuberculosis to isoniazid (INH), rifampin (RIF), streptomycin (SM) and ethambutol (EMB) was evaluated by comparing MGIT results to those obtained by the method of proportion. Fify-four isolates of M. tuberculosis including 30 strains selected for resistance were tested. The MGIT-AST method was performed according to the manufacturer's recommendations: inoculum was obtained from culture on Loewenstein-Jensen slant, the final concentrations tested were 0.1, 1, 0.8 and 3.5 μg/ml for INH, RIF, SM and EMB respectively. All tubes were examined daily between 3 t h and 14 t h day on a 365-nm UV transilluminator, an isolate was susceptible if the drug-containing tube did not fluoresce within two days after the growth control tube fluoresced. To resolve discrepancies, MGIT and proportion method were repeated.The mean time to MGIT results was 7.9 days. The contamination was 0.4%. Both methods agreed for 48 isolates (89%). The results agreed for the 54 strains for EMB [23 resistant (R)/ 31 susceptible (S)] and RIF [3R/51S]. With SM MGIT and method of proportion results agreed for 50 [17R/33S], but four were resistant by method of proportion and susceptible by MGIT. For three strains, a fluorescence was detected in the SM containing tube 24 or 48 h after the line of two days. With EMB both methods agreed for 51 isolates [3R/48S], but three were resistant by method of proportion and susceptible by MGIT. The MGIT gives rapid and concordant results with method of proportion. It could be constitued an alternative to method of proportion for susceptibility testing to INH and RIF. Additional studies demonstrate the ability of MGIT for EMB and SM susceptibility testing. At the present time, pyrazinamid cannot be studied. Because its sensitivity to contamination, MGIT is reserved to specialized laboratories.