Factors contribute to efficiency of specimen concentration of Mycobacterium tuberculosis by centrifugation and magnetic beads.

Background: A concentration of specimen is recommended for the effective recovery of Mycobacterium tuberculosis (MTB), but the bacteriological efficiency is not well evaluated. The present study evaluated the factors contributing to concentration efficiency of centrifugation and bead-based technique (TB-Beads; Microsens, UK) to recover MTB by using simple in vitro specimens.

Methods: Four specimens were prepared (6.5×10(3); 8.1×10(4); 7.9×10(5); and 6.4×10(6)cfu/mL) of different concentrations with or without 5×10(4) of THP-1 cells (RIKEN BRC, Japan). Specimens were subjected to centrifugation at 2000, 3000, and 4000g for 15min, and to TB-Beads. The concentration and recovery rate were calculated to evaluate the efficiency of each method.

Results: The specimens containing a higher number of bacteria and THP-1 cells had a tendency to yield a higher concentration and recovery rate (p=0.001-0.083). MTB was recovered more efficiently with THP-1 cells from the 6.5×10(3)cfu/mL specimen by centrifugation (p⩽0.001) than without them; 24.7-54.4% of MTB were recovered with THP-1 cells by centrifugation at 3000g for 15min, while the recovery using TB-Beads was a maximum of 12.7%.

Conclusions: The efficiency of centrifugation depends on the bacterial density and the co-existence of THP-1 cells. The efficiency of TB-Beads was not as high as centrifugation.