A comparison of the Bactec 9000MB system and the Septi-Chek AFB system for the detection of mycobacteria

The Bactec MB9000 (MB) continuous monitoring system was compared to the Septic-Chek AFB (SC) for the detection of Mycobacterium species from all patient sources. A total of 1485 specimens were evaluated. Two hundred forty-eight specimens grew mycobacteria in one or both systems. The isolates recovered were 18 Mycobacterium tuberculosis (MTB), 109 M. avium complex (MAC), 59 M. fortuitum-chelonae complex (MFC), 51 pigmented mycobacteria (PGM), and 11 nonpigmented mycobacteria, not MTB/MAC (NP). Of the 248 positive specimens, 157 were positive in both systems; 73 in the SC only; and 18 in the MB only. The mean times to detection for specimens were 11.5 days for MB versus 16.4 days for SC. The false positivity rate in the MB was 5.8%. Contamination rates for the MB and the SC were 12.7% and 19.8%, respectively. These data suggest that the automated MB system has clear advantages over the manual SC system in terms of earlier time to detection of significant mycobacteria, less technical hands-on time, and a lower contamination rate.