ABILITY OF PCR ASSAY TO IDENTIFY MYCOBACTERIUM-TUBERCULOSIS IN BACTEC-12B VIALS

Introduction of PCR to directly detect Mycobacterium tuberculosis in c linical specimens has shown promise; however, interfering substances i n clinical material have contributed to lowered assay sensitivities. W e evaluated the ability of a PCR assay to detect M. tuberculosis in BA CTEC 12B broth cultures. Clinical specimens were processed and inocula ted into BACTEC 12B vials. Evaluation was approached in two phases, st arting with an initial evaluation in which an aliquot of 12B broth was removed,when the growth index (GI) was greater than or equal to 10 an d stored at 4 degrees C until assayed by PCR. Of the 290 specimens ini tially assayed, 129 were culture negative for mycobacteria as well as PCR negative for M. tuberculosis. Except for one, cultures (n = 102) w hich grew mycobacteria other than M. tuberculosis were all PCR negativ e. The remaining 59 broths were all culture and PCR positive for M. tu berculosis; 39% (n = 23) of these cultures when assayed by PCR had GIs of less than or equal to 50. Following initial evaluation, 200 12B BA CTEC vials with GIs of less than or equal to 10 were assayed in a simi lar manner except that specimens were amplified twice weekly to determ ine PCR's impact on the length of time to identification of M. tubercu losis as compared with standard laboratory practices. Utilization of P CR resulted in a mean time to detection of M. tuberculosis of 14 days, compared with 29 days by using commercially available nucleic acid pr obes to identify M. tuberculosis complex from growth of BACTEC 12B sub cultures on solid media. In light of an overall sensitivity and specif icity of 100 and 99.7%, respectively, coupled with the ability to iden tify M. tuberculosis days or weeks before other methods can be applied , we conclude that PCR might prove to be a rapid alternative for ident ification of M. tuberculosis in culture and allow for earlier setup of susceptibility testing.