Performance of mycobacterium growth indicator tube incubated at 30°C for detection of mycobacteria in CF and tissue samples compared to conventional growth conditions of liquid and solid media

Background

Mycobacterial culture using mycobacterium growth indicator tube (MGIT) liquid culture incubated at 36°C has a superior performance for mycobacteria detection compared to solid media. For cystic fibrosis (CF) patients and tissue samples incubation at 30°C may additionally improve performance. We evaluate MGIT incubated at 30°C compared to MGIT 36°C and solid media incubated at 36°C and 30°C in samples from CF patients and tissue samples.

Methods

All samples (n=1446) of CF patients and tissue samples submitted for mycobacterial diagnostics between February 2021 and September 2023 to the University Medicine Essen were inoculated on MGIT liquid medium (Becton Dickinson), Lowenstein Jensen (LJ) and Stonebrink solid media with PACT (Oxoid, Wesel, Germany) and were incubated at both temperatures, 30°C and 36°C. MGIT cultured at 36°C were incubated in a Bactec MGIT 960TM device (Becton Dickinson) for 6 weeks, all other cultures were incubated for 8 weeks. MGIT 30°C cultures were incubated in a 30°C incubator and analysed for growth using MicroMGIT reader (BD). Ziehl-Neelsen staining was primarily performed for all positive cultures to confirm mycobacterial growth. Identification of mycobacteria was primarily performed using GenoType CM, AS or NTM-DR (Hain Lifescience).

Results

Of 1446 samples, a total of 187 mycobacterial isolates were cultured. The highest detection rate was from MGIT 30°C with 86.1% (161 of 187 mycobacterial isolates). MGIT 36°C recovered 59.8% (112 of 187), LJ 36°C 48,1% (90), Stonebrink 36°C 50.8% (95), LJ 30°C 50.3% (94) and Stonebrink 30°C 55.1% (103) of grown isolates. MGIT 30°C detected 34 mycobacterial isolates that were not recovered by any other culture condition. MGIT 30°C detected the highest number of isolates for M. abscessus complex (39), M. chelonae (6), M. chimaera (20), M. fortuitum (1), M. gordonae (21), M. intermedium (1), M. mucogenicum (3), M. simiae complex (1), M. spec. (6), M. nebraskense (1) and M. tuberculosis (23).

Conclusions

For CF patients and tissue samples, MGIT cultivated at 30°C for eight weeks improves performance of mycobacterial culture.