[Evaluation of an automatic system (MB/BacT) for the isolation of Mycobacterium spp]

The study purpose was to evaluate the MB/BacT automated system against Löwenstein-Jensen solid media for the isolation of Mycobacterium species.

1,511 specimens were processed from 15/10/96 to 28/4/97. For digestion and decontamination NALC-NaOH was used. Auramine smear was performed and both culture media were inoculated after digestion-decontamination. Inoculation on MB/BacT bottles was performed according to the manufacturer's instructions, apart from a modification in MAS antibiotic supplement with the addition of vancomycin at 1 microgram/ml as final concentraction. Both media were incubated for 40 days at 37 degrees C.

In total 101 (6.6%) mycobacteria species were isolated. 78 M. tuberculosis, 14 M. avium, 6 M. gordonae, 2 M. chelonae and 1 M. fortuitum. 98 (6.4%) Mycobacterium spp. were isolated in MB/BacT and 79 (5.2%) were isolated in Löwenstein-Jensen. 22 (1.4%) out of 101 grew only in MB/BacT and 3 (0.2%) out of 101 grew only in Löwenstein-Jensen. Sensitivity in MB/BacT was 97% compared to 78% in Löwenstein-Jensen, this difference was estatically significant (p < 0.001). Contamination rate was 1.8% in MB/BacT and 13.3% in Löwentein-Jensen. The average time to detection of Mycobacterium spp. was 15.9 days in MB/BacT and 22.4 in Löwenstein-Jensen.

We believe that MB/BacT is a good system for rapid and reliable detection of Mycobacterium spp.