Method -Sputum samples included in the study were direct smear positive with a minimum
volume of 5 ml. Samples were thinned for 15 min by addition of an equal volume of
NaOH/NALC. Samples were then divided into two 5 ml volumes. One 5 ml volume of thinned
sputum was placed through the TB-Bead protocol which takes less than 5 min and does
not involve centrifugation. The final eluate was adjusted to 0.5 ml with phosphate
buffer and 50 µl analysed on a slide by auramine and ZN acid-fast stain. The other
5 ml of thinned sputum was made up to 50 ml with phosphate buffer and then centrifuged
for 20 min. The pellet was resuspended in 20 ml phosphate buffer and the sample recentrifuged
as before. Finally, the pellet was adjusted to 0.5 ml with phosphate buffer and 50
µl analysed on a slide by auramine and ZN acid-fast stain.
Results -The figures in the table show the total number of acid-fast mycobacteria
counted in 20 fields using a 40x objective.
Conclusion -The results show that concentration of mycobacteria from sputum using
either centrifugation or TB-Beads are comparable and that, as expected, both show
a higher concentration of mycobacetria on the slide than direct smear. In both concentration
methods, the mycobacteria were resuspended in a relatively large volume of liquid
in order to facilitate counting. In practice, more concentrated and more sensitive
smears could be performed by reducing the volume of the resuspension buffer.
* * * * * * * * *
Investigation of the concentration of mycobacteria from sputum using TB-Beads compared
In this issue we look at a study that compares TB-Beads with centrifugation for the
concentration of mycobacteria from sputum. In the next issue we will discuss different
disinfectants for TB.
Rationale - To compare the ability of centrifugation and TB-Beads to concentrate
mycobacteria from sputum as determined by ZN and auramine microscopy