Buoyant density of Mycobacterium tuberculosis: implications for sputum processing.

Area of Science:

• Microbiology
• Biophysics

Background:

• Mycobacterium tuberculosis (TB) cell concentration from sputum typically uses centrifugation after chemical liquefaction.
• Effective sedimentation relies on the buoyant density of TB cells relative to sputum.

Purpose of the Study:

• To measure the buoyant density of cultured Mycobacterium tuberculosis cells.
• To determine optimal centrifugation times and speeds for pelleting mycobacteria.

Main Methods:

• Cultured M. tuberculosis strains in various systems.
• Measured the buoyant density of M. tuberculosis cells.
• Calculated necessary centrifuge times and speeds for effective pelleting.

Main Results:

• No M. tuberculosis cells with buoyant density <1 g/cm(3) were identified, contrary to some reports.
• Measured buoyant densities ranged from 1.02 to 1.13 g/cm(3).
• Lower density cells may better represent clinically derived mycobacteria.

Conclusions:

• Effective sedimentation of M. tuberculosis requires approximately 22 minutes at 3200 x g.
• Further studies using clinical samples are needed to confirm these findings.
• Lower speeds or shorter centrifugation times are unlikely to yield effective recovery.