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Investigating the potential of biosurfactants in the control of tooth infections

Hashim, Zahraa 2019. Investigating the potential of biosurfactants in the control of tooth infections. PhD Thesis, Cardiff University.
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Abstract

A shift from the “doomed” organ concept of an exposed pulp to the concept of hope and retrieval has been recently adopted with the introduction of vital pulp therapy. Microbial contamination of the capped pulp is the main cause of therapy failure and is a fundamental challenge of contemporary endodontics. Biosurfactants are tensioactive microbe-derived molecules with a potential antimicrobial/antiadhesive activity. This project aimed to investigate the role of biosurfactants, specifically probiotic-derived ones and a commercial-sourced rhamnolipid (Sigma Aldrich), as novel endodontic antimicrobial therapies that can aid in reducing the incidence of infection and endodontic failure. Of five probiotic strains studied, Lactobacillus plantarum demonstrated significant antimicrobial activity against three Streptococcus anginosus group members; S. anginosus, S. constellatus and S. intermedius and against Enterococcus faecalis. A cell-bound biosurfactant (Lp-BS) was successfully extracted from the potential probiotic L. plantarum. Biochemical characterisation identified Lp-BS as a glycoprotein molecule that was capable of reducing surface tension and emulsifying hydrocarbons. For the endodontic pathogens studied, Lp-BS demonstrated no antibacterial activity up to concentrations of 50 mg/ml, but displayed significant antiadhesive potential at 20 mg/mL. Proteomic analysis revealed a rich heterogeneous proteinaceous nature of Lp-BS mixture and importantly identified three adhesin-like proteins raising the possibility for applications in pathogenic bacterial adhesion interference. Ten mg/ml Lp-BS induced high levels of apoptosis in pulpal fibroblasts at 24 h, resulting in significant reduction in cell number. No significant differences were reported in cell counts or histology of pulp tissue treated with 0.625-10 mg/mL Lp-BS in comparison to the controls, over a 24 h time period. Subsequent incubation with 10 mg/mL for 48 h revealed obvious pulp tissue toxicity. Partial purification of Lp-BS by means of size-exclusion chromatography resulted in five elution pools with the first fraction determined to retain the biosurfactant activity; this fraction can be further investigated for antimicrobial/antiadhesive effects. Rhamnolipid demonstrated substantial antimicrobial effect with minimum inhibitory concentrations determined to be 0.097 mg/mL against S. anginosus, 0.048 mg/mL against S. constellatus and S. intermedius and 50 mg/mL against E. faecalis. Rhamnolipid also reduced attachment of S. anginosus and S. intermedius to an abiotic surface. Of importance, rhamnolipid was shown to tolerate serum concentrations ≤ 5 % v/v. However, above this concentration inactivation of rhamnolipid effect was demonstrated. Application of rhamnolipid to rodent ex-vivo tooth model infected with S. anginosus and S. constellatus demonstrated significant antimicrobial activity and a mild immune response of pulp tissue in response to treatment was documented. This work provides the foundation for further investigation on Lp-BS adhesin-like proteins as a novel endodontic antiadhesive therapy. Furthermore, the cost-effective rhamnolipid with its antimicrobial and immune-modulatory effect covers two fundamental requirements of pulp tissue repair and therefore, opens future prospects for novel biosurfactants application in pulp therapy.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Dentistry
Subjects: Q Science > Q Science (General)
Uncontrolled Keywords: probiotics, plantarum, biosurfactants, rhamnolipid, Lp-BS, antiadhesion, antimicrobial, dental pulp, pulpitis
Date of First Compliant Deposit: 29 August 2019
Last Modified: 29 Aug 2019 14:15
URI: http://orca-mwe.cf.ac.uk/id/eprint/125180

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