Clinical evaluation of Difco ESP culture system II for growth and detection of mycobacteria

The reliability of the ESP Culture System II (ESP II; Difco Laboratories, Detroit, Mich.), a continuously monitoring mycobacterial culture system, was evaluated by comparing its performance,vith the BACTEC TB 460 (BACTEC TB) and Middlebrook 7H11/7H11 selective agar systems. A total of 2,283 specimens of all types (70.7% were respiratory specimens) were cultured; 149 (6.5%) yielded mycobacteria. The most common species recovered were Mycobacterium avium complex (MAC, 73 isolates) and Mycobacterium tuberculosis complex (MTBC, 53 isolates). The recovery rates by individual system were 87, 81, and 65% for ESP II, BACTEC TB, and Middlebrook agar, respectively, for all mycobacteria; the recovery rates were 89, 92, and 89%, respectively, for MTBC. For liquid plus solid medium system combinations, recovery rates for all mycobacteria and for MTBC, respectively, were 91 and 94% for ESP II plus Middlebrook agar and 85 and 96% for BACTEC TB plus Middlebrook agar. The difference between the recovery rates of all mycobacteria by ESP II and by BACTEC TB was not significant, whereas for the individual species, the only significant difference was recovery of more isolates of MAC by ESP II. For those isolates recovered in the individual systems, mean times to detection of all mycobacteria, MTBC, and MAC, respectively, were 13.1, 15.5, and 10.9 days for ESP II; 14.4, 16.6, and 12.1 days for BACTEC TB; and 17.8, 18.3, and 18.8 days for Middlebrook agar. ESP II is a reliable, nonradiometric, less labor-intensive alternative to BACTEC TB for growth and detection of mycobacteria, but as with other liquid culture methods, ESP II should be used in combination with a solid medium, not as a stand-alone system.