High centrifugation speed improves recovery of M. tuberculosis and yield of culture

Abstract

Background

We assessed the impact of centrifugation on recovery of Mycobacterium tuberculosis (M.tb).

Methods

We used 0.5 McFarland from the 2 weeks M. tb, H37Rv culture and homogenized sputum for our experiments. Samples were decontaminated by 2 % NaOH for 20 min and with PBS for controls. Decontaminated aliquots were centrifuged at 2000×g, 3000×g and 6000×g for 40 min and inoculated on MGIT and LJ media. MGITs were incubated into the BACTEC MGIT 960 Systems following BD manuals and data analyzed on GraphPad Software.

Results

The positivity (days) for M. tb, H37Rv in MGIT and LJ decreased from 20.4 to 17.7 and from 47.6 to 26.6 at 2000×g and 6000×g, respectively; P > 0.05. For controls, MGIT and LJ positivity (days) decreased from 19 to 10 and from 39.2 to 11.2 at 2000×g and 6000×g, respectively; P > 0.05. MGIT positivity was 6(60 %) at 2000×g and 8(80 %) at 6000×g, corresponding to mean (±SD) of 13.7 ± 6.7 and 9.06 ± 4.6 days, respectively for sputum. LJ positivity was 1(10 %) at 2000×g and 7(70 %) at 6000×g. MGIT contamination for controls (sputum) was over 50 % and 80 % for LJ.

Conclusion

Higher centrifugation speed improves yield and sensitivity of TB culture.