Mycobacteria naturally grow as corded biofilms in liquid media without detergent. Such detergent-free biofilm phenotypes may reflect the growth pattern of bacilli in tuberculous lung lesions. New strategies are required to treat tuberculosis, which is responsible for more deaths each year than any other bacterial disease. The lengthy 6-month regimen for drug-sensitive tuberculosis is necessary to remove antimicrobial drug tolerant populations of bacilli that persist through drug therapy. The role of biofilm-like growth in the generation of these sub-populations remains poorly understood despite the hypothesised clinical significance and mounting evidence of biofilms in pathogenesis. We adapt a three-dimensional Rotary Cell Culture System to model M. bovis BCG biofilm growth in low-shear detergent-free liquid suspension. Importantly, biofilms form without attachment to artificial surfaces and without severe nutrient starvation or environmental stress. Biofilm-derived planktonic bacilli are tolerant to isoniazid and streptomycin, but not rifampicin. This phenotypic drug tolerance is lost after passage in drug-free media. Transcriptional profiling reveals induction of cell surface regulators, sigE and BCG_0559c alongside the ESX-5 secretion apparatus in these low-shear liquid-suspension biofilms. This study engineers and characterises mycobacteria grown as a suspended biofilm, illuminating new drug discovery pathways for this deadly disease.
Bibliographical noteFunding Information:
S.J.W. would like to acknowledge funding from The Royal Society (research grant RG110191). D.C. was funded by a University of Brighton PhD studentship. The authors thank Dr Julian R. Thorpe in the Electron Microscopy Division, University of Sussex, Dr. Chris Jones for statistical support, Dr. Ben Alberts for guidance with ELISA experiments, and Dr. Adam Witney and Dr. Kate Gould in the Bacterial Microarray Group at St George’s, University of London. Figure 1 and Supplementary Figure 1 were created with BioRender (www.biorender.com).
© 2021, The Author(s).
Copyright 2021 Elsevier B.V., All rights reserved.
- Mycobacterium bovis