Rapid susceptibility testing of Mycobacterium tuberculosis by the Mycobacteria Growth Indicator Tube (MGITAST SIRE)

ObjectiveTo evaluate the reliability of the Mycobacteria Growth Indicator Tube (MGITAST) for susceptibility testing of Mycobacterium tuberculosis.MethodsSeventy strains of M. tuberculosis were tested for susceptibility to streptomycin, isoniazid, rifampicin and ethambutol by comparing MGITAST results to those obtained by the method of proportion (MOP) on Lowenstein–Jensen (LJ) and Middlebrook 7H10 media. The 7H10 MOP was considered the method of reference.ResultsThe turnaround time for MGITAST was 6.2days (5–10days) and for MOP it was 18–21days. With rifampicin, MGITAST agreed for all isolates with both MOP. For streptomycin, MGITAST and 7H10 MOP agreed for 64 isolates (91.4%); 61 were susceptible and three resistant. LJ MOP and 7H10 MOP agreed for 64 isolates (92.2%); 62 were susceptible and three resistant. With isoniazid, both MOP agreed for all isolates, while MGITAST and 7H10 MOP had two discrepancies. For ethambutol, MGITAST and 7H10 MOP were concordant for 66 isolates; 65 were susceptible and one resistant. Both MOP were concordant for 67 isolates; 66 were susceptible and one resistant.ConclusionsBased on these results, MGITAST is a time-saving method and can be used as an alternative to the BACTEC System. MGITAST is reliable as far as rifampicin and isoniazid are concerned; however, additional studies are needed for streptomycin and ethambutol