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Journal of Clinical Microbiology, June 2006, p. 2314-2315, Vol. 44, No. 6
0095-1137/06/$08.00+0     doi:10.1128/JCM.00712-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

LETTER TO THE EDITOR

Does the MGIT 960 System Improve the Turnaround Times for Growth Detection and Susceptibility Testing of the Mycobacterium tuberculosis Complex?

Top Letter References

 
The nonradiometric and fully automated Mycobacteria Growth Indicator Tube 960 system (MGIT 960; Becton Dickinson Microbiology Systems, Sparks, MD) has been proposed as a more efficient alternative to the semiautomated and radiometric BACTEC 460TB system (4, 5). However, it is noteworthy that to date, only two prospective studies (1, 2) have examined the turnaround time (TAT) of the first-generation protocol (the manual 4-ml MGIT) for this assay with respect to both growth detection and susceptibility testing of the Mycobacterium tuberculosis complex (MTBC). Importantly, those studies assessed only a limited number of samples drawn from repositories, rather than actual patient specimens, and only one of the two compared the MGIT with the BACTEC system (1). Similar studies to assess the performance of the fully automated 7-ml MGIT 960 have not yet been reported. Since the health care provider has to make decisions concerning discontinuation of certain drugs or significantly changing the drug regimen upon receipt of susceptibility testing results, it is important that the entire TAT be examined, from specimen collection (or receipt in the laboratory) through reporting of susceptibility results.

A prospective study was performed using 260 consecutive MTBC Fast Track clinical specimens (253 M. tuberculosis, 4 Mycobacterium africanum, and 3 Mycobacterium bovis) in a routine diagnostic setting to determine the TATs of the MGIT 960 system relative to the reference BACTEC 460TB system for growth detection, susceptibility testing, and specimen processing (from specimen receipt to reporting of susceptibility testing results) of MTBC.

The model Fast Track program for tuberculosis was initiated by the New York State Department of Health in 1993 to expedite testing of newly diagnosed smear positive, and therefore highly infectious, patients (3). After decontamination, the following media were inoculated for each specimen: one MGIT 960 tube, one BACTEC 12B vial, and one Lowenstein-Jensen Gruft slant. Growth detection and drug susceptibility testing assays using the automated MGIT 960 system and the reference BACTEC method were performed in line with the recommendations of the manufacturer (4, 6).

Of the 260 specimens, 29 were excluded from TAT calculations either due to nonmycobacterial contamination (20 [7.7%] specimens) or due to being a mixed culture with Mycobacterium avium (9 specimens [3.5%]). Of the remaining 231 specimens, 193 (83.5%) yielded pansusceptible MTBC, and 38 (16.6%) yielded drug-resistant MTBC. There was a statistically significant difference (P < 0.0001) in the mean TAT from specimen receipt to the detection of growth of MTBC between the MGIT 960 (8.6 days; range, 2 to 33 days) and the BACTEC system (6.4 days; range, 1 to 23 days).

An additional 29 specimens were omitted from the comparative analysis, in line with the instructions of the manufacturer, on the basis of delayed (>5 days after growth detection) MGIT 960 susceptibility setup (10 [4.3%] specimens), invalid susceptibility results with the MGIT 960 system (13 [5.6%] specimens), or invalid susceptibility results with the BACTEC 460TB system (3 [1.3%] specimens). In addition, in three (1.3%) specimens, growth was detected more than 4 days earlier in the MGIT 960 system than in the BACTEC system. For ethical reasons, MGIT 960 aliquots were transferred into the BACTEC susceptibility testing system to avoid further delays. MGIT 960 susceptibility testing produced an invalid result for one isolate of M. africanum (25%) and for one isolate of M. bovis (33%). These numbers are not significant, and additional research studies are clearly warranted to determine the suitability of the MGIT for detection of all members of the MTBC.

For the remaining 202 specimens, the mean TATs for susceptibility testing (from setup through reporting of susceptibility results) were 7.3 days (range, 5 to 12 days) with the MGIT 960 system and 4.3 days (range, 3 to 10 days) with the BACTEC 460TB system (P = 0.015, a significant difference). The mean TATs from specimen receipt to reporting of susceptibility results were 17.9 days (range, 10 to 47 days) with the MGIT 960 system and 14.6 days (range, 5 to 34 days) with the BACTEC system (P < 0.0001, a significant difference) (Fig. 1).

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FIG. 1. The number and distribution of mycobacterial isolates having total turnaround times (from specimen receipt through reporting of susceptibility results) either longer and shorter than the mean turnaround time ± standard error for the MGIT 960 and BACTEC 460TB systems.

The guidelines of the Centers for Disease Control and Prevention recommend that the TAT for susceptibility testing of MTBC be 2 to 4 weeks following receipt of the specimen (7). In the present study, this recommended TAT could be achieved for 75.0% of the 260 Fast Track specimens with the MGIT 960 system and for 76.5% of the specimens with the BACTEC 460TB system. Thus, although the MGIT 960 system brings increased safety, new technology, and more economical use of labor, it does not introduce any significant improvement that would benefit patient treatment compared to the radiometric BACTEC method. Therefore, we would encourage the manufacturer to modify the MGIT 960 system to produce shorter TATs, while retaining the advantages of its more efficient and safety-minded design. This, however, is likely to be a short-term gain, given that new goals outlined in Healthy People 2010 have proposed a detection time of 2 days for 75% of all tuberculosis cases (9, 10). It is imperative, therefore, that the clinical mycobacteriology laboratories pursue more-sensitive nucleic acid amplification assays in conjunction with molecular drug susceptibility assays that are performed directly on the clinical specimens. Such approaches will inevitably replace the growth detection-based systems (6, 8).

Top Letter References

 

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1. Ardito, F., M. Sanguinetti, L. Sechi, B. Posteraro, L. Masucci, G. Fadda, and S. Zanetti. 2000. Comparison of the mycobacteria growth indicator tube with radiometric and solid culture for isolation of mycobacteria from clinical specimens and susceptibility testing of Mycobacterium tuberculosis. New Microbiol. 23:151-158.[Medline]
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2. Goloubeva, V., M. Lecocq, P. Lassowsky, F. Matthys, F. Portaels, and I. Bastian. 2001. Evaluation of Mycobacteria Growth Indicator Tube for direct and indirect drug susceptibility testing of Mycobacterium tuberculosis from respiratory specimens in a Siberian prison hospital. J. Clin. Microbiol. 39:1501-1505.[Abstract/Free Full Text]
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3. Hale, Y. M., E. P. Desmond, K. C. Jost, Jr., and M. Salfinger. 2000. Access to newer laboratory procedures: a call for action. Int. J. Tuberc. Lung Dis. 4:S171-S175.[Medline]
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4. Kontos, F., M. Maniati, C. Costopoulos, Z. Gitti, S. Nicolaou, E. Petinaki, S. Anagnostou, I. Tselentis, and A. N. Maniatis. 2004. Evaluation of the fully automated Bactec MGIT 960 system for the susceptibility testing of Mycobacterium tuberculosis to first-line drugs: a multicenter study. J. Microbiol. Methods 56:291-294.[Medline]
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5. Scarparo, C., P. Ricordi, G. Ruggiero, and P. Piccoli. 2004. Evaluation of the fully automated BACTEC MGIT 960 system for testing susceptibility of Mycobacterium tuberculosis to pyrazinamide, streptomycin, isoniazid, rifampin, and ethambutol and comparison with the radiometric BACTEC 460TB method. J. Clin. Microbiol. 42:1109-1114.[Abstract/Free Full Text]
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6. Somoskovi, A., Q. Song, J. Mester, C. Tanner, Y. M. Hale, L. M. Parsons, and M. Salfinger. 2003. Use of molecular methods to identify the Mycobacterium tuberculosis complex (MTBC) and other mycobacterial species and to detect rifampin resistance in MTBC isolates following growth detection with the BACTEC MGIT 960 system. J. Clin. Microbiol. 41:2822-2826.[Abstract/Free Full Text]
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7. Styrt, B. A., T. M. Shinnick, J. C. Ridderhof, J. T. Crawford, and F. C. Tenover. 1997. Turnaround times for mycobacterial cultures. J. Clin. Microbiol. 35:1041-1042.[Medline]
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8. Takakura, S., S. Tsuchiya, N. Fujihara, T. Kudo, Y. Iinuma, S. Mitarai, S. Ichiyama, K. Yasukawa, and T. Ishiguro. 2005. Isothermal RNA sequence amplification method for rapid antituberculosis drug susceptibility testing of Mycobacterium tuberculosis. J. Clin. Microbiol. 43:2489-2491.[Abstract/Free Full Text]
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9. U.S. Department of Health and Human Services. 2000. Healthy people 2010, 1st ed., vol. I. U.S. Department of Health and Human Services, Washington, D.C.
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10. U.S. Department of Health and Human Services. 2000. Healthy people 2010, 1st ed., vol. II. U.S. Department of Health and Human Services, Washington, D.C.

						Akos Somoskovi Anne Clobridge Susan C. Larsen Wadsworth Center New York State Department of Health Albany, New York,1 Oleg Sinyavskiy Department of Clinical and Laboratory Diagnosis Kazakh National Medical University Almaty, Kazakhstan,2 Suheyla Surucuoglu Department of Microbiology and Clinical Microbiology Medical School Celal Bayar University Manisa, Turkey,3 Linda M. Parsons International Laboratory Branch Global AIDS Program Centers for Disease Control and Prevention Atlanta, Georgia,4 Max Salfinger*
						* Phone: (518) 474-2196, Fax: (518) 474-6964, E-mail: salfinger{at}wadsworth.org

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Journal of Clinical Microbiology, June 2006, p. 2314-2315, Vol. 44, No. 6
0095-1137/06/$08.00+0     doi:10.1128/JCM.00712-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

This article has been cited by other articles:

• Parrish, N., Osterhout, G., Dionne, K., Sweeney, A., Kwiatkowski, N., Carroll, K., Jost, K. C. Jr., Dick, J. (2007). Rapid, Standardized Method for Determination of Mycobacterium tuberculosis Drug Susceptibility by Use of Mycolic Acid Analysis. J. Clin. Microbiol. 45: 3915-3920 [Abstract] [Full Text]  

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Somoskovi, A. Articles by Salfinger, M. Search for Related Content PubMed PubMed Citation Articles by Somoskovi, A. Articles by Salfinger, M.