Characterization of competition between commensal A2 and clinical A1 strains of Enterococcus faecium

Abstract

Enterococcus faecium (E. faecium) emerged from a gut commensal to one of the leading nosocomial multidrug-resistant pathogens. The species of E. faecium, has a deep phylogenetic split into commensal and clinical strains. The dominance of clinical strains during nosocomial infections is only insufficiently understood. Previous studies revealed competitive characteristics between the commensal and clinical clade. This thesis aimed to study interaction and competition dynamics in vitro between a diverse range of different strains of commensal and clinical E. faecium clades. For the commensals, the focus was set on clade A2. Competitive growth on agar plates was carried out to determine inhibition grades between competing strains. Furthermore, the degree of inhibition mediated by bacterial supernatant combined with different stress treatments was investigated. Previous studies suggested proteinaceous and heat-stable secreted compounds, such as bacteriocins, which might be involved in mediating inhibition. On genome level, bacteriocins were predicted using the bacteriocin prediction database BAGEL4. It was shown that diverse clinical clade A1 and commensal clade A2 E. faecium strains generally could outcompete each other in some cases. Clinical strains showed a higher inhibition frequency and most of them could be associated with hospital-leading lineages. Some commensal strains showed high inhibition and at the same time resistance of being inhibited towards a whole range of clinical strains. Most of these inhibitions could be associated with secreted proteinaceous, heat-stable compounds, most likely bacteriocins. However, a lot of bacteriocins or other secreted compounds which might mediate E. faecium inhibition remain unknown and further studies are needed.