Effect of transportation and acid neutralization on recovery of mycobacteria from processed specimens

Because of the increasing incidence of tuberculosis, more rapid detection of mycobacteria has become an important issue. Realizing that not every clinical laboratory has a rapid detection system for growing mycobacteria, this study was conducted to examine the feasibility of submitting sediments of processed specimens to a reference laboratory for further testing in a radiometric system. Using N-acetyl-L-cysteine-NaOH solution, 247 respiratory specimens were processed at a diagnostic laboratory. Half of each sediment was cultured on conventional media. The remainder was kept at 4 degrees C for a period of up to 1 week before transportation to a reference laboratory for culture by BACTEC system. Both laboratories recovered 25 organisms: 15 as Mycobacterium tuberculosis (MT) and 10 as M avium complex (MAC). Additionally, mycobacteria (MT[3], MAC[6], M gordonae [4], and M fortuitum [1]) were recovered from 14 specimens by the diagnostic laboratory that were not grown by the reference laboratory. These results indicate a significant decrease in viability of mycobacteria after processing of the specimens. Acid neutralization of the digested respiratory sediments significantly improved the recovery rate of mycobacteria even after 2 days of delay in culture. This preliminary work suggests that more extensive studies will provide useful information to delineate approaches to submitting neutralized sediments for mycobacterial cultures.