What Can You do When the AFB Culture is Lost? Send the Slides to California
By Alan D. Tice, MD, FACP
Source: Patnaik M, et al. Rapid detection of smear-negative Mycobacterium tuberculosis by PCR and sequencing for rifampin resistance with DNA extracted directly from slides. J Clin Microbiol. 2001;39:51-52.
Patnaik and associates of the reseach department of Specialty Laboratories in Santa Monica, Calif, seem to have perfected a way to detect Mycobacterium tuberculosis from slides of expectorated sputum using PCR. They can even detect the gene for resistance to rifampin.
They studied routine specimens sent to their laboratory for mycobacteria stains and cultures. They also used a technique of eluting mycobacterial DNA from sputum slides, then sequenced the rpoB gene to determine rifampin resistance as well. The nested PCR method could be done with a turnaround time of 48 hours.
Of 47 sputum specimens submitted for acid-fast bacilli (AFB) smears and culture, 24 (51%) grew M tuberculosis. Only 14 (58%) were detected by microscopic methods. All 24 were positive by the PCR technique. There were no false-positives. PCR also detected all 5 strains with rifampin resistance.
This technique sounds good when the AFB culture is lost or not done. If more specimens confirm these numbers, it could also be used for much more rapid results for the detection of M tuberculosis as well as susceptibility testing.