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°C) using Löwenstein-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.


CONCLUSIONS
None of the culture techniques independently (both before and after storage) detected growth of MTB 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.
Department of Microbiology, MMIMSR, MM University, Mullana, Ambala, Haryana, India. shinup1983@gmail.com.
Pottathil
P
Shinu
Department of Microbiology, MMIMSR, MM University, Mullana, Ambala, Haryana, India.
Varsha
V
AshokKumar Singh
Department of Pharmaceutical Sciences, College of Clinical Pharmacy, King Faisal University, Al-Ahsa, Kingdom of Saudi Arabia.
Anroop
A
Nair
Department of Microbiology, MMIMSR, MM University, Mullana, Ambala, Haryana, India.
Rumana
R
Farooq
Department of Biochemistry, MMIMSR, MM University, Mullana, Ambala, Haryana, India.
Sheikh
S
Ishaq
D001431:Bacteriological Techniques / Q000379:methods*; D005260:Female; D005615:Freezing; D006801:Humans; D008297:Male; D009169:Mycobacterium tuberculosis / Q000302:isolation & purification* / Q000472:pathogenicity; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology*; D013997:Time Factors; D014397:Tuberculosis, Pulmonary / Q000175:diagnosis*
LJ media; MB 7H11 agar; MGITTM system; Mycobacterium tuberculosis; long-term storage
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