Comparison of Isolation of Mycobacterium tuberculosis from various clinical samples using liquidculture (MGIT) and PCR targeting IS6110 gene

Abstract

Tuberculosis, one of the oldest recorded human afflictions, still one of the biggest killers among the infectious diseases, despite the worldwide use of a live attenuated vaccine and several antibiotics. The Aim of this study was to isolate Mycobacterium tuberculosis from various clinical samples using liquid culture (MGIT) and confirm the growth as MTB using Polymerase chain reaction (PCR).
Material and Methods: All 85 samples were received from clinically suspected cases of pulmonary and extrapulmonary tuberculosis from the various clinical departments of SGRRIM&HS, Dehradun over a period of one year. All samples were processed by ZN staining, culture in LJ medium & MGIT, rapid card (BD MGIT TBcID) test and PCR done by using IS6110gene.
Result: Out of total 85 samples, 35 (41%) came out to be positive by PCR and 50 (59%) cases were found to be negative. Correlation of ZN smear with MGIT culture: 2 cases (2%) were positive in both ZN stain and MGIT culture but 24 (28%) cases showed positivity in MGIT culture. Correlation of MGIT culture with PCR: 24 cases (28%) showed positivity in both MGIT culture and PCR.11 cases (13%) showed positivity in PCR but negative in MGIT culture. The positivity rate was 28% (24/85) in MGIT culture & 41% (35/85) in PCR.
Conclusion: Our study clearly reflects that PCR finding are more positive as compared to MGIT and ZN staining. Because of high specificity and sensitivity of PCR few MTB DNA can be easily detected which is not possible in MGIT and ZN staining. Techniques like PCR is highly valuable for detection of Mycobacterium tuberculosis but the limitation is that it can’t differentiate between live and dead bacteria.