Characterization of competition between commensal and clinical strains of Enterococcus faecium

Abstract

Invasive infection by multidrug-resistant Enterococcus faecium is increasingly becoming a healthcare concern. Few studies have addressed whether and how clinical E. faecium strains are able to outcompete commensal strains. This thesis aimed to characterize the in vitro competition between commensal and clinical E. faecium strains with respect to growth inhibition exerted by bacteriocins produced by the respective strain groups. A combination of laboratory assays and bioinformatical methods were applied toward this goal. Laboratory assays consisted of competitively growing commensal and clinical E. faecium strains, and using unmodified and modified supernatants from the same strains to investigate the nature of growth inhibition-mediating agents. The bioinformatical methods consisted of genetic relationship analyses and ribosomally synthesized post-translationally modified peptide-mining. It was shown that clinical E. faecium strains generally outcompete commensal E. faecium strains in vitro, though the commensal E. faecium strains that inhibit the growth of clinical E. faecium strains most often, do so very strongly. Furthermore, some commensal and clinical E. faecium strains possibly encoding novel bacteriocins were identified. Finally some commensal E. faecium strains that were resistant to the growth-inhibiting mechanisms of most epidemic and hospital-associated clinical E. faecium strains were found.