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

BackgroundA 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.MethodsFour specimens were prepared (6.5 × 103; 8.1 × 104; 7.9 × 105; and 6.4 × 106 cfu/mL) of different concentrations with or without 5 × 104 of THP-1 cells (RIKEN BRC, Japan). Specimens were subjected to centrifugation at 2000, 3000, and 4000g for 15 min, and to TB-Beads. The concentration and recovery rate were calculated to evaluate the efficiency of each method.ResultsThe 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 × 103 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 15 min, while the recovery using TB-Beads was a maximum of 12.7%.ConclusionsThe 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.