Original Research

Storage of Mycobacterium tuberculosis culture isolates in MicrobankTM beads at a South African laboratory

Anura David, Lesley E. Scott, Pedro Da Silva, Elizabeth Mayne, Wendy S. Stevens
African Journal of Laboratory Medicine | Vol 12, No 1 | a2172 | DOI: https://doi.org/10.4102/ajlm.v12i1.2172 | © 2023 Anura David, Lesley E. Scott, Pedro Da Silva, Elizabeth Mayne, Wendy S. Stevens | This work is licensed under CC Attribution 4.0
Submitted: 28 January 2023 | Published: 25 October 2023

About the author(s)

Anura David, Wits Diagnostic Innovation Hub, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
Lesley E. Scott, Wits Diagnostic Innovation Hub, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
Pedro Da Silva, National Priority Program, National Health Laboratory Services, Johannesburg, South Africa
Elizabeth Mayne, National Priority Program, National Health Laboratory Services, Johannesburg, South Africa; and, Division of Immunology, University of Cape Town, Cape Town, South Africa
Wendy S. Stevens, Wits Diagnostic Innovation Hub, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa; and, National Priority Program, National Health Laboratory Services, Johannesburg, South Africa

Abstract

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. MicrobankTM 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 MicrobankTM 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 MicrobankTM 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: MicrobankTM beads will allow for the reculture of up to 25 culture isolates using a reduced culture volume compared to current storage methods. MicrobankTM beads represent a storage solution for the medium-term storage of MTBC isolates.

What this study adds: This study evaluated the use of MicrobankTM 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

Sustainable Development Goal

Goal 3: Good health and well-being

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