Microsens Medtech Ltd., London Bioscience Innovation Centre, 2 Royal College Street London, NW1 0NH

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Method - Four smear positive sputum samples ranging from thick to thin in consistency were investigated following the TB-Beads protocol. 5 ml of each thinned sputum were analysed.

Investigation of the efficiency of capture. TB-Beads were added to the sputum to capture any mycobacteria. After magnetic removal of the TB-Beads along with any mycobacteria captured to these beads, the remaining thinned sputum was diluted to 50 ml with distilled water and then centrifuged for 20 min. After decanting the supernatant, the whole pellet was then investigated by acid fast microscopy.

Investigation of the efficiency of the wash. The TB-Beads were washed in 10 mM NaOH as described in the TB-Bead protocol. The beads with any retained mycobacteria were collected on a magnet and the wash poured off. The wash was subjected to a further magnetic capture in order to remove any residual beads. The wash was then diluted to 20 ml with distilled water and centrifuged for 20 min. After decanting the supernatant, the whole pellet was then investigated by acid fast microscopy.

Investigation of capture. After the wash was decanted, some wash solution remained with the beads. This was adjusted to 300µl with 10mM NaOH in order to standardise the volume. The mycobacteria bound to the beads were then eluted with 100 µl of Elution Buffer and 50µl investigated by acid fast microscopy. Therefore in total 1/8th of the eluate (50µl from a total volume of 400µl) was analysed by microscopy.


Results - The numbers of mycobacteria were counted in a total of 20 fields observed using a 40x objective. The percentage efficiency was determined related to the numbers of mycobacteria observed in the final eluate.


Conclusion - The capture of mycobacteria from thinned sputum is extremely efficient with few if any mycobacteria observed post-capture. The wash recovers around 80% or more of the captured mycobacteria but there is some loss in this wash step. Overall, the loss in the wash step coupled with the extremely nigh efficiency of capture is unlikely to affect the microscopy results. An alternative wash buffer that shows no loss at this step has been developed by us, is under evaluation and gives us the option of improving the wash efficiency of future versions of the TB-Bead kit.



* An occasional bacilli was observed on the slide

^ number of mycobacteria observed in 20 fields x 8 in order to estimate the total number of mycobacteria recovered.

NA, not applicable


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Microsens Medtech

Investigation of the capture and wash efficiency of TB-Beads for  capture  of mycobacteria from sputum


Customers have asked us about the efficiency of capture of mycobacteria using TB-Beads. In this issue of Consumption we include a study that was performed to answer this question.

Rationale - To investigate the efficiency of capture of mycobacteria from sputum and to investigate the efficiency of the wash step.



Consumption  March 2011/1