Improved detection times for Mycobacterium avium complex and Mycobacterium tuberculosis with the BACTEC radiometric system

Abstract

A total of 2,559 routine clinical specimens were cultured for mycobacteria by using BACTEC Middlebrook 7H12 medium (BACTEC), Lowenstein-Jensen slants (LJ), and Mycobactosel selective Middlebrook 7H11 slants (M7H11). Thirty-three isolates (1.3%) of M. avium complex and 82 isolates (3.2%) of M. tuberculosis were recovered. The BACTEC mean detection time of M. avium complex from 27 smear-negative specimens was earlier than that of conventional media for both decontaminated respiratory specimens (BACTEC, 12 days; LJ, 32 days; and M7H11, 38 days) and untreated tissue and fluid specimens (BACTEC, 8 days; LJ, 30 days; and M7H11, 31 days). The sensitivity for smear-negative M. avium complex with BACTEC (74%) was comparable to that with LJ (74%) and M7H11 (63%). The mean detection times of M. tuberculosis from 56 smear-positive respiratory specimens were 8 days for BACTEC, 16 days for LJ, and 17 days for M7H11, and sensitivities for the detection of positive cultures were 98% for BACTEC, 76% for LJ, and 79% for M7H11. The BACTEC mean detection time of M. tuberculosis in smear-negative specimens was better for tissues and fluids (14 days) than for respiratory specimens (24 days). BACTEC yielded substantially earlier detection of M. avium complex from all specimen types and of M. tuberculosis from smear-positive respiratory specimens. The rapid identification and susceptibility testing of M. tuberculosis in BACTEC agreed completely with conventional tests and provided a 3-week reduction in median time to final reports.