Evaluation of a new blood culture medium for mycobacteria

This study evaluates the sensitivity and detection time of a new radiometric broth (BACTEC 13A medium, Johnston Laboratories, Towson, MD) designed for direct blood culturing for Mycobacteria. A total of 1,848 blood specimens were cultured in parallel by a new method in which blood was directly inoculated into 13A medium and a comparative method involving lysis-centrifugation and inoculation of 7H11 agar and 7H12 broth media. There were 65 blood cultures with positive results (64 Mycobacterium avium-intracellulare and 1 Mycobacterium tuberculosis) from 43 patients. For the direct inoculation and lysis-centrifugation methods, the recovery rates were 96.9% and 98.5%, respectively, and the mean times to detection were essentially the same (23.6 and 23.8 days, respectively). Thus, the direct-inoculation technique using 13A medium showed performance equivalent to the lysis-centrifugation method. Also, the direct method has the advantage of elimination of the time-consuming manual manipulations that are required by lysis-centrifugation methods.