Tuberculosis (TB) is a contagious infection caused by the bacterium Mycobacterium tuberculosis [1]. Despite significant advances in diagnosis and treatment, TB remains a leading cause of morbidity and mortality worldwide. Rapid and accurate detection of TB is critical for effective treatment and control of the disease [2]. Traditional culture methods, though considered the gold standard, are time-consuming and labor-intensive [3]. The MGIT 960 system, an automated liquid culture system, has been developed to address these challenges by providing quicker and more reliable results [4].     

Sample Collection and Processing

Sputum specimens were collected in sterile plastic screw-capped centrifuge tubes. The specimens were subjected to digestion and decontamination using the N-Acetyl-L-cysteine/sodium hydroxide (NALC-NaOH) method. This method involves the following steps [5]:

• Digestion: The sputum is treated with a digestant solution to free TB bacilli from mucus cells

• Decontamination: Sodium hydroxide (NaOH) is used to eliminate normal flora that could interfere with TB recovery

• Homogenization and Concentration: The digested specimens are homogenized and centrifuged to concentrate the TB bacilli

Reagent Preparation

Reagents for TB culture, including 4% NaOH, 2.9% sodium citrate and 0.067M phosphate buffer (PBS) at pH 6.8, were prepared according to standardized protocols. The working solution (0.5% NALC-NaOH) was freshly prepared for each batch of samples.

Culture and Identification

The processed specimens were inoculated into MGIT 960 tubes, which were then loaded into the MGIT 960 machine. The machine automatically monitors the tubes for fluorescence, indicating bacterial growth. Positive cultures were further examined for the presence of Mycobacterium tuberculosis using the TBcID kit, which detects the MPT64 antigen specific to TB.

The MGIT 960 system provided rapid detection of Mycobacterium tuberculosis, significantly reducing the time to positive results compared to traditional solid culture methods. Most positive cultures were detected within 7-10 days. The system's automation allowed for the processing of multiple samples simultaneously, enhancing laboratory throughput and efficiency. Quality control measures, including the use of positive (ATCC 25177) and negative (ATCC 25922) controls, ensured the reliability of the results.

The MGIT 960 system has proven to be an effective tool for TB diagnosis, offering several advantages over traditional methods. Its rapid detection capabilities are particularly beneficial in high-burden settings, where timely diagnosis is crucial for controlling the spread of TB. The system's automation reduces the hands-on time required for sample processing, allowing laboratory personnel to focus on other critical tasks. Furthermore, the use of the TBcID kit for the identification of Mycobacterium tuberculosis ensures the specificity of the results.

The MGIT 960 automated liquid culture system represents a significant advancement in the field of TB diagnostics. Its ability to provide rapid, reliable results with minimal manual intervention makes it an ideal choice for laboratories seeking to improve their diagnostic capabilities. Continued use and further refinement of this technology will contribute to better TB control and management globally.

1. Chakaya, J. et al. “Global tuberculosis report 2020—reflections on the global Tb burden, treatment and prevention efforts.” International Journal of Infectious Diseases, vol. 113, December 2021, pp. S7–S12.

2. Maynard-Smith, L. et al. “Diagnostic accuracy of the Xpert MTB/RIF assay for extrapulmonary and pulmonary tuberculosis when testing non-respiratory samples: A systematic review.” BMC Infectious Diseases, vol. 14, December 2014, pp. 1–5.

3. Held, M. et al. “Diagnostic accuracy of the xpert MTB/RIF assay for extrapulmonary tuberculosis in children with musculoskeletal infections.” The Pediatric Infectious Disease Journal, vol. 35, no. 11, November 2016, pp. 1165–1168.

4. Siddiqi, S.H. and S. Rüsch-Gerdes. Mycobacteria Growth Indicator Tube (MGIT) Culture and Drug Susceptibility Demonstration Projects: For BACTEC™ MGIT 960™ TB System. Foundation for Innovative New Diagnostics (FIND), July 2006.

5. Parmar, A. et al. “Advances in clinical diagnosis of tuberculosis: past, present and future.” Strategies to Overcome Superbug Invasions: Emerging Research and Opportunities, 2021, pp. 66–90.