Rapid recovery of mycobacteria from clinical specimens using automated radiometric technic

Automated radiometric technic (BACTEC Johnston Laboratories, Towson, MD) was compared with conventional mycobacterial culture procedure (Lowenstein-Jensen plus Gruft modification of Lowenstein-Jensen) in this study of 1,000 clinical specimens. In addition, 8-azaguanine inhibition was tested by radiometric technic as a rapid procedure for the differentiation of Mycobacterium tuberculosis from other mycobacterial species. A total of 59 mycobacteria was recovered. Of 28 clinically significant isolates (M. tuberculosis, M. kansasii, M. avium, M. fortuitum), the BACTEC system detected 26 (93%). Conventional methods recovered 23 (82%). The BACTEC system required an average of seven days to recover M. tuberculosis from smear-positive specimens compared with 18 days required by Lowenstein-Jensen or Gruft slants. From smear-negative specimens, the BACTEC detected M. tuberculosis in an average of 20 days versus 28 days by conventional procedure. All 20 isolates of M. tuberculosis were inhibited by 8-azaguanine, whereas 39 isolates of mycobacteria other than M. tuberculosis were not inhibited. The BACTEC system accomplishes more rapid recovery of mycobacteria and provides a higher yield than conventional methods.