Evaluation of four mycobacterial blood culture media: BACTEC 13A, Isolator/BACTEC 12B, Isolator/Middlebrook agar, and a biphasic medium.

Four commercially available mycobacterial blood culture systems were compared for sensitivity and time to detection of growth. A 5-ml volume of SPS-anticoagulated blood was cultured in a BACTEC 13A vial and a modified M7H11/BHI biphasic medium. In addition, two aliquots of Isolator concentrates, each derived from 5 ml of blood, were inoculated into a BACTEC 12B vial and onto a pair of Middlebrook 7H11 agar plates (M7H11). Mycobacteria were recovered from 32 of 180 cultured specimens (17.8%). Growth was detected in 30 (93.7%) of the 13A vials, 27 (84.4%) of the M7H11 agar plates, 26 (81.2%) of the 12B vials, and 14 (43.8%) of the biphasic bottles. The mean times to growth detection in the 13A vial (14.2 days) and the 12B vial (13.7 days) were shorter than in either the M7H11 plates (20.8 days) or the biphasic medium (24.1 days). When the Isolator/12B vial-and-M7H11 plates were evaluated as a single system, 29 cultures (90.6%) had a mean time to growth detection of 13.5 days. Colony-forming units per ml were inversely associated with time to growth detection. Delay in transport (greater than 24 h) appeared to reduce viability. The direct inoculation feature makes the 13A vial very suitable for mycobacterial blood cultures.