Direct identification of Mycobacterium avium complex and Mycobacterium gordonae from MB/BacT bottles using AccuProbe

We evaluated the ability of the AccuProbe (Gen-Probe, San Diego, Calif) to detect Mycobacterium gordonae and Mycobacterium avium complex directly in l iquid medium flagged positive by the MB/BacT (Organon Teknika Corp., Durham , N.C.). Seventy-one bottles from clinical specimens containing M. goldonae , and 34 containing M. avium, confirmed by culture, were tested by direct A ccuProbe assay for both organisms after additional incubation for greater t han or equal to 48 h and centrifugation at 4,500 x g for 15 min. Relative l ight unit (RLU) values were analyzed using the manufacturer's recommended c utoff of 30,000 RLU and a lower cutoff of 10,000 RLU. Using the 30,000 RLU cutoff, 55 of 71 (77.5%) specimens containing M gordonae yielded positive r esults, whereas 28 of 34 (82.3%) M. avium complex specimens were correctly identified by direct probe. No specimens shown by culture to contain either M. gordonae or M. avium complex tested positive with the probe for the opp osite organism (100% specificity). When the cutoff was lowered to 10,000 RL U, 67 of 71 M. gordonae (94.4%) and 32 of 34 M. avium complex (94.1%) speci mens were correctly identified. This difference was significant for M. gord onae (P = 0.004) but not for M. avium complex (P = 0.26) compared to detect ion using the recommended RLU cutoff. Specificity was 100% for specimens co ntaining M. gordonae that were tested with the M. avium complex probe using the 10,000 RLU cutoff, whereas specificity for specimens containing M. avi um complex tested with the M. gordonae probe was 97%, Using a lower RLU cut off for determining a positive result using the M. gordonae or M. avium com plex probes when testing instrument-positive MB/BacT battles directly will improve sensitivity without substantially compromising specificity.