Amhimmid, Mohammed
(2023)
Investigating antimicrobial resistance by competition of Staphylococcus species.
PhD thesis, University of Liverpool.
|
Text
201365005_June2023.pdf - Author Accepted Manuscript Download (18MB) | Preview |
Abstract
Staphylococcus aureus can invade the human skin microflora and cause many serious infections as an opportunistic pathogen. The anterior nares are its major niche where it colonises with diverse bacteria that interact and compete for the same resources and binding sites. The study of microbial competition and invasion increases our understanding of species dynamics and how they contribute to evolution of antibiotic resistance and impacts on human health. However, the genetic drivers in the evolution of competition and resistance remains unclear in the S. aureus niche. A deferred growth inhibition assay was used to determine the antimicrobial activities of coagulase- negative Staphylococcus (CoNS) species, including S. capitis and S. lugdunensis, which were determined to have novel genes for Biosynthetic Gene Clusters (BGS). Two species competition (co-culture) was explored to simulate the competition environment among species isolated from human skin and those species with novel BGS. Experimental evolution of interference competition was used to identify mutations selected during co-culture. Illumina platform genome resequencing of S. aureus clones identified multiple single nucleotide polymorphisms (SNPs) including several candidate resistance genes. In co-culture with the unidentified antimicrobial producer S. capitis 47, S. aureus strains SH1000 and 184 evolved mutations in the repressor gene cro/cI that was previously demonstrated to regulate an efflux transporter, supporting that S. aureus might use this efflux pump system to survive this antimicrobial activity in competition with other producer species. During serial passages of S. aureus SH1000 and 184 strains, further mutations were selected in the agr and sigB genes that reduced pigment production. In a separate coculture investigation with the epifadin antimicrobial producer S. epidermidis IVK83, S. aureus USA300 showed experimentally evolved resistance with mutation in the two-component system (TCS), desK gene. The DesKR TCS was recently implicated in epifadin resistance during a study in our research group at Liverpool. This study extends our knowledge into the strain USA300. A further co-culture competition was performed with S. aureus USA300 and antimicrobial producer S. lugdunensis 1007. While confirming existing data that S. aureus could not evolve resistance to lugdunin but there were selected mutations that supported increased fitness. The S. aureus mutations identified in the Cro/CI repressor, DesKR TCS and those in response to a lugdunin producer indicate there are an array of mechanisms concerned with interspecific competition. Commensal bacteria are an important resource of molecules and antimicrobials to study for preventing staphylococcal infections.
| Item Type: | Thesis (PhD) |
|---|---|
| Divisions: | Faculty of Health and Life Sciences |
| Depositing User: | Symplectic Admin |
| Date Deposited: | 11 Aug 2023 14:51 |
| Last Modified: | 11 Aug 2023 14:52 |
| DOI: | 10.17638/03171369 |
| Supervisors: |
|
| URI: | https://livrepository.liverpool.ac.uk/id/eprint/3171369 |
Dimensions
Dimensions
