An in vitro investigation of Mycobacterium tuberculosis biofilm formation and its effect on the host innate immune response

• Main Author: Keating, Thomas Oliver
• Published: University of Birmingham 2018
• Subjects: QR180 Immunology
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760322

Mycobacterium tuberculosis is ostensibly an intracellular pathogen, which may form pellicle-like biofilms in the peripheries of tuberculosis cavities. Environment-induced cell wall modifications and extracellular polymeric substance production may alter host-pathogen interactions. Specifically, expectorated mycobacteria from cavities, which establish infection in new hosts, may have distinct phenotypic adaptations to impair early clearance by the innate immune system. M. tuberculosis H37Rv biofilm extracellular polymeric substance was identified using scanning electron microscopy. Biofilm phenotype non-covalently-bound extracts of cell wall lipids and carbohydrates were compared to planktonic phenotype and a relative reduction in the proportion of constituent glucose in biofilm carbohydrate extracts was discovered, indicative of a reduction in α-glucan prevalence. Comparison of carbohydrate extracts’ potency in stimulating cytokine and chemokine secretion in whole blood and complement activation elucidated reduced C3b/iC3b deposition onto biofilm carbohydrate extracts. Labelling live dispersed M. tuberculosis planktonic and biofilm samples with fluorescent antibodies showed C3b/iC3b, C5b-9, MBL and C1q deposition was reduced on biofilm phenotype cells, using flow cytometry. The relative contribution of each major pathway of complement activation was investigated and greater dependence on classical pathway activation by M. tuberculosis biofilm cells compared to planktonic cells was observed. Implications of these findings in M. tuberculosis pathogenesis are discussed.