Long-Term Storage at-80°C: Effect on Rate of Recovery of Mycobacterium tuberculosis From Direct Acid-Fast Bacilli Smear-Positive Sputum Samples

Background: The aim of this study was to evaluate the difference in the rate of recovery of Mycobacterium tuberculosis (MTB) from routinely cultured sputum and long-term stored sputum specimens (at -80 degrees C) using Lowenstein-Jensen (LJ) media, Mycobacterium Growth Indicator Tube (BBL MGIT (TM)), and Middlebrook 7H11 (MB 7H11) agar. Methods: Direct acid-fast bacilli smear-positive sputum specimens (both before and after storage [n = 136]) were studied (after culturing on LJ media, BBL MGIT (TM), and MB 7H11 agar) and the performances were compared. Results: For the detection of MTB, BBL MGIT (TM) and MB 7H11 agar (before storage) demonstrated a sensitivity, specificity, positive predictive value (PPV) of 98.28%, 30.77%, 92.68%, 66.67%, and negative predictive value (NPV) of 97.41%, 30.77%, 92.62%, 57.14%, respectively, when compared to LJ media (before storage). Similarly, BBL MGIT (TM) and MB 7H11 agar (after storage) demonstrated a sensitivity, specificity, PPV, and NPV of 95.5%, 38.89%, 90.6%, 58.33%, and 95.5%, 66.67 %, 94.64%, 70.59%, respectively, when compared to LJ media (after storage) for the detection of MTB. Conclusion: None of the culture techniques independently (both before and after storage) detected growth ofMTB from all the sputum specimens studied. However, BBL MGIT (TM) system and LJ media combination (both before and after storage) effectively detected the growth of MTB from sputum specimens when compared to other culture technique combinations. (C) 2015 Wiley Periodicals, Inc.