Comparison of the Proportion Method With Mycobacteria Growth Indicator Tube and E-test for Susceptibility Testing of Mycobacterium tuberculosis

Abstract

The aim of this study was to investigate the correlation between proportion method with mycobacteria growth indicator tube (MGIT) and E-test for Mycobacterium tuberculosis. Forty clinical isolates were tested. MGIT and Etest with the first line antituberculous drugs correlated with the proportion method. Our results suggested that MGIT and E-test methods can be routinely used instead of the proportion method.Key words: Mycobacterium tuberculosis -E-test -mycobacteria growth indicator tubeThe resurgence of tuberculosis and outbreaks of multidrug-resistant Mycobacterium tuberculosis has increased the emphasis on rapid turn-round time for mycobacterial cultures and susceptibility testing for effective treatment and control of the disease (Zapata et al. 1999).The proportion method (on Middlebrook 7H10-11 agar) and Bactec TB 460 system (Becton Dickinson Microbiology System, Cockeysville, MD, USA) are the most commonly used methods to determine drug susceptibility of M. tuberculosis (NCCLS 1995). Recently, new methods were developed including, BBL mycobacteria growth indicator tube (MGIT) (Becton Dickinson Microbiology System) and E-test (AB BIODISK) (Palaci et al. 1996, Wanger & Mills 1996. The purpose of this study was to compare the proportion method with MGIT and E-test for susceptibility testing of M. tuberculosis.Forty clinical isolates were tested using the proportion method, MGIT and E-test. Agar dilution susceptibility testing was performed according to the proportion method as described NCCLS tentative standard-M24-T (NCCLS 1995). M. tuberculosis H37Rv, susceptible to all antimicrobials, were included as control strain. E-test susceptibility testing was performed as described by Wanger and Mills (1996). MGIT susceptibility testing was performed according to the protocol provided by the manufacturer and as described elsewhere (Palaci et al. 1996). The results were compared using Kappa (measurement of agreement) and Mc Nemar statistical tests. Table. The correlations between E-test/ MGIT with the agar proportion method were 84.4/79.5, 90.8/82.8, 85.7/80.8 and 77.3/82.8 % for isoniazid, rifampicin, streptomycin and ethambutol, respectively. There were no significant differences between the proportion method and E-test and MGIT susceptibility testing. The average time required to obtain susceptibility results were 6 days for MGIT, 7 days for E-test and 21 days for the agar proportion method. In case of discordances, the tests were repeated, and no difference was noted on the susceptibility profiles. Among all plates, used on E-test, only one had contamination, which necessitated the repeat of the experiment.The commonly used agar proportion method for mycobacterial susceptibility testing requires a three-week period of incubation before an isolate can be reported as drug susceptible. However, the Bactec radiometric susceptibility method has the advantage of being more rapid than the agar proportion method (4-7 days) but it requires the use of radioisotopes and can be costly to perform (Sanic et al. 2000). Wan...

Drug susceptibility testing of Mycobacterium tuberculosis with nitrate reductase assay

“…Recently, new methods for drug susceptibility testing of M. tuberculosis have been described, including MGIT, the E test, Alamar blue, and nucleic acid base methods (Walters & Hanna 1996, Wagner & Mills 1996, Collins & Franzblau 1997, Birinci et al 2002. However, some of these methods are expensive and require special equipment (Leite et al 2000).…”

“…The proportion method requires 3 weeks of incubation. The Bactec TB system uses a broth medium containing radiolabeled palmitic acid substrate and results can be reported in 4-7 days, but it is labor-intensive, expensive, and generates radioactive waste (Zapata et al 1999, NCCLS 2002, Birinci et al 2002.…”

Susceptibility Rates of Pulmonary and Extrapulmonary 229 Mycobacterium tuberculosis Isolates to Major Antituberculous Drugs and Comparison of E test and Standard Proportion Methods

“…In the se stu di es, E test met hod was empha si zed as a fast, easy, re li ab le, and fe a sib le method for ro u ti ne use in de tec ting an timy co bac te ri al sus cep ti bi lity. 11,12,19,21,24 Ak ca li et al ha ve al so found an ex cel lent ag re e ment for INH, RIF, SM and EMB (100%) with E test and agar pro por ti on results in the ir study. 19 In anot her study, Mu ra lid har et al sug ges ted that cor re la ti on bet we en L-J propor ti on and E test met hod was 87%.…”

Comparison of the Mycobacterium Growth Indicator Tube Method and the Method of Proportion for Drug Susceptibility Testing of Mycobacterium Tuberculosis

“…MGIT, a broth-based non-radiometric system is an alternative to the radiometric system. By adding M. tuberculosis suspension to a drug-containing MGIT tubes, an anti-mycobacterial susceptibility test (AST) can be [15] found a better correlation between MGIT and MOP on LJ medium. Said et al [16] reported that the MGIT 960 system performed well for SM and EMB when compared to MOP (sensitivity in detecting resistance 95% and 92%, respectively).…”