Investigating the determinants of Enterococcus faecalis virulence in Drosophila melanogaster
File(s)
Author(s)
Wadhawan, Ashima Deepak
Type
Thesis
Abstract
Enterococcus faecalis is a Gram-positive bacterium found in the normal gut microbiota of diverse species, including vertebrates and invertebrates, as well as being common in the environment. It is also an opportunistic pathogen with a broad host range. One of the hosts E. faecalis can infect is the fruit fly, Drosophila melanogaster. The Drosophila immune response is distinct from that of humans and interacts with E. faecalis differently. To study this interaction we carried out experimental evolution via serial passage of E. faecalis in Drosophila. We generated E. faecalis strains with much-enhanced ability to survive and proliferate within this host. Strains selected in this way are specifically resistant to the Toll-induced Bomanin family of effector peptides, resulting not only in higher E. faecalis numbers but also in a significant increase in pathogenicity. Many of these Drosophila-selected strains also exhibit marked increases or decreases in antimicrobial resistance. Whole genome sequencing showed that most selected strains carried single mutations and that many of these mutations were in genes encoding proteins known to be involved in bacterial surface characteristics and antimicrobial resistance (mprF_2, liaF, yxdM, croS, bgsA). To test if Drosophila antimicrobial peptides kill E. faecalis using mechanisms similar to antibiotics we generated E. faecalis strains that were resistant to daptomycin. Some of these daptomycin-adapted strains also acquired resistance to the Drosophila immune response. Daptomycin-adapted E. faecalis strains have mutations in the same genes or the same regulatory systems as were observed in Drosophila-adapted strains. As common genetic mechanisms underlie the resistance of E. faecalis to daptomycin and the Drosophila immune response, these results indicate these two systems target the same conserved bacterial properties in E. faecalis. They also demonstrate that the selection and emergence of antibiotic resistance in vivo does not require antibiotic exposure.
Version
Open Access
Date Issued
2022-12
Date Awarded
2023-05
Copyright Statement
Creative Commons Attribution NonCommercial Licence
License URL
Advisor
Dionne, Marc
Publisher Department
Life Sciences
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)