Comparison of methods for identification of Mycobacterium abscessus and M-chelonae isolates

Mycobacterium abscessus and Mycobacterium chelonae are two closely related species that are often not distinguished by clinical laboratories despite t he fact they cause diseases requiring different treatment regimens. Multilo cus enzyme electrophoresis, PCR-restriction fragment length polymorphism an alysis of the 65-kDa heat shock protein gene, biochemical tests, and high-p erformance liquid chromatography of mycolic acids were used to identify 75 isolates as either M. abscessus or M. chelonae that were originally submitt ed for drug susceptibility testing. Only 36 of these isolates were submitte d with an identification at the species level. Using the above methods, 46 of the isolates were found to be M. abscessus and 29 were identified as M. chelonae. Eight isolates originally submitted as M. chelonae were identifie d as M. abscessus, and one isolate submitted as M. abscessus was found to b e M. chelonae. The four identification methods were in agreement in identif ying 74 of the 75 isolates. In drug susceptibility testing, all isolates of M. abscessus exhibited resistance to tobramycin (MIC of 8 to greater than or equal to 16 mug/ml), while all isolates of M. chelonae were susceptible to this drug (MIC of less than or equal to4 mug/ml). The results suggest th at once an identification method is selected, clinical laboratories should be able to easily identify isolates of M. abscessus and M. chelonae.