Background:
Non-tuberculous mycobacteria (NTM) also known as atypical mycobacteria, anonymous mycobacteria, and mycobacteria other than Mycobacterium tuberculosis are acid fast bacilli ubiquitous in the environment. These pathogens have emerged as significant pathogens of chronic pulmonary infection as well extra pulmonary infection in the last three decades. Although people with prior tuberculosis, chronic obstructive pulmonary disease, cystic fibrosis and immunocompromised are at highest risk, however recent studies have shown that many immunocompetent without such diseases are genetically susceptible to infection with NTM.
In USA for example, incidence of NTM respiratory infection has increased from 4.8 per 100.000 in 2007 to 5.6 in 2012. In Canada the incidence of NTM respiratory infection being estimated at 9.8 per 100.000 in 2010.
Although the introduction of fully automated Bactec MGIT 320 system and VITEK MS system have reduced the time of mycobacterium species isolation, however, subculture of liquid medium onto solid medium is still required to isolate mycobacterium colonies before proceeding with appropriate identification method and this poses another challenges in terms of time saving, appropriate antibiotics administration, and cost saving.
Objectives:
In this study, we assessed the accuracy and precision of Vitek MS IVD version 3.2 in identification of Mycobacterium species DIRECTLY from liquid medium (MGIT BROTH), using high speed preparation methods in order to enhance the turnaround time TAT of Mycobacterium species identification, therefore, expedite the treatment plan. This is being done as part of the validation for this process/technique.
Materials and Methods:
We analyzed 53 tuberculosis nontuberculous mycobacterial samples of 14 different known species using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of isolates grown from SOLID Lowenstein–Jensen medium and MGIT medium using high speed centrifugation.
Results/Expected Results:
Direct identification of Mycobcaterium species form liquid medium using MALDI-TOF VITEK MS v.3.2, showed high accuracy up to 88% (47/53) for sample preparations using high speed centrifugation compared to identification from solid medium using MALDI-TOF VITEK MS v.3.2 , PCR method, and CAP samples. The accuracy to identify M. tuberculosis was 100% (14/14) compared to PCR method (Genexpert). The precision was assessed by Intra-assay variability across three runs of five mycobacterium species performed by the same technologist on the same day. Inter-day variability was assessed across three runsof five mycobacterium species performed by the same technologist across three consecutive days. The precision showed xx% in the intra-asay and xx% in the inter-day assay.
Conclusion and Significance of outcome:
Identification of Mycobaterium species directly from liquid medium has been shown to be accurate and precise rapid method that can be included within the routine of TB LAB flow in order to expedite the identification and therefore, faster, effective, and targeted intervention..
Refernces:
- Kolibab K, Yang A, Parra M, Derrick SC, Morris SL. Time to detection of Mycobacterium tuberculosis using the MGIT 320 system correlates with colony counting in preclinical testing of new vaccines. Clin Vaccine Immunol. 2014 Mar;21(3):453-5. doi: 10.1128/CVI.00742-13. Epub 2013 Dec 26. PMID: 24371256; PMCID: PMC3957671.
- World Health Organization 2012. Global tuberculosis report. World Health Organization, Geneva, Switzerland
- Lin SY, Desmond E, Rienthong S, Rienthong D, Boonin C. 2013. Evaluation of the BD Bactec MGIT 320 for detection of mycobacteria and drug susceptibility testing of Mycobacterium tuberculosis. J. Clin. Microbiol. 51:3403–3405. 10.1128/JCM.01357-13
- Luo L, Liang L, Zhang R, Chen W, Yu F, Zhao Y, Yue J. Using Vitek MS v3.0 To Identify Nontuberculous Mycobacteria in Liquid Media in a Clinical Microbiology Laboratory. Microbiol Spectr. 2022 Dec 21;10(6):e0201822. doi: 10.1128/spectrum.02018-22. Epub 2022 Oct 26. PMID: 36287015; PMCID: PMC9769768.
Direct Identification of Mycobcaterium species Form liquid medium using MALDI
Evan John