Comparison of methods for isolating Mycobacterium avium-intracellulare from blood of patients with AIDS.

A variety of blood culture media were compared to determine the optimal method for the isolation of Mycobacterium avium-intracellulare (MAI) from the blood of patients with AIDS. Simulated laboratory blood cultures and clinical blood cultures were tested. Glucose broth, Bactec aerobic medium, Kirschner's medium, and Bactec Middlebrook medium supported the growth of MAI. The Isolator system, a lysis centrifugation method, facilitated the most rapid isolation of MAI (p = 0.001). The Bactec Middlebrook medium gave the most rapid detection rate (p = 0.001) as acid fast bacilli could be stained by the Ziehl-Neelson method before colonies were isolated in the Isolator system. The growth index readings did not reliably predict mycobacterial growth in the two radiometric media tested. Although several methods may be used to isolate MAI from blood, the most rapid and sensitive method is the Isolator system used in combination with the Bactec Middlebrook medium.