Abstract

DAVID, Anura et al. Storage of Mycobacterium tuberculosis culture isolates in Microbank^TM beads at a South African laboratory. Afr. J. Lab. Med. [online]. 2023, vol.12, n.1, pp.1-6. ISSN 2225-2010.  http://dx.doi.org/10.4102/ajlm.v12i1.2172.

BACKGROUND: Mycobacterium tuberculosis complex (MTBC) isolates are typically stored at −70 °C in cryovials containing 1 mL aliquots of a liquid medium, with or without 50% glycerol. Multiple uses of the culture stock may decrease the strain viability while increasing the risk of culture contamination. Small culture aliquots may be more practical; however, storage capacity remains challenging. Microbank^TM beads (25 beads/vial) for the long-term storage of fungal cultures is well documented, but their use for storing MTBC isolates is uninvestigated OBJECTIVE: The study aimed to determine the feasibility of using Microbank^TM beads for long-term storage of MTBC isolates at a laboratory in South Africa. METHODS: In February 2020, 20 isolates in liquid culture were stored in Microbank^TM beads, following an in-house developed protocol, at −70 °C. At defined time points (16 months [15 June 2021] and 21 months [18 November 2021]), two beads were retrieved from each storage vial and assessed for viability and level of contamination. RESULTS: Stored liquid isolates demonstrated MTBC growth within an average time-to-detection of 18 days following retrieval, even at 21 months post storage. Contaminating organisms were detected in 2 of 80 (2.5%) culture isolates. CONCLUSION: Microbank^TM beads will allow for the reculture of up to 25 culture isolates using a reduced culture volume compared to current storage methods. Microbank^TM beads represent a storage solution for the medium-term storage of MTBC isolates. What this study adds: This study evaluated the use of Microbank^TM beads as an alternate method for storing MTBC culture isolates at −70 °C and provided a suitable option for medium-term storage of MTBC.

Keywords : Mycobacterium tuberculosis; culture isolates; storage; liquid culture; Microbank beads.

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