Functional characterization of a gene cluster responsible for inositol catabolism associated with hospital-adapted isolates of Enterococcus faecium .

is a nosocomial, multidrug-resistant pathogen. Whole genome sequence studies revealed that hospital-associated isolates are clustered in a separate clade A1. Here, we investigated the distribution, integration site and function of a putative gene cluster that encodes for inositol (MI) catabolism. This gene cluster was found as part of an ~20 kbp genetic element ( element), integrated in ICE close to its integrase gene in isolate E1679. Among 1644 isolates, ICE was found in 789/1227 (64.3 %) clade A1 and 3/417 (0.7 %) non-clade A1 isolates. The element was present at a similar integration site in 180/792 (22.7 %) ICE-containing isolates. Examination of the phylogenetic tree revealed genetically closely related isolates that differed in presence/absence of ICE and/or element, suggesting either independent acquisition or loss of both elements. gene cluster containing isolates E1679 and E1504 were able to grow in minimal medium with only -inositol as carbon source, while the -deficient mutant in E1504 (E1504∆) lost this ability and an gene cluster negative recipient strain gained this ability after acquisition of ICE by conjugation from donor strain E1679. Gene expression profiling revealed that the gene cluster is only expressed in the absence of other carbon sources. In an intestinal colonization mouse model the colonization ability of E1504∆ mutant was not affected relative to the wild-type E1504 strain. In conclusion, we describe and functionally characterise a gene cluster involved in MI catabolism that is associated with the ICE island in hospital-associated isolates. We were unable to show that this gene cluster provides a competitive advantage during gut colonisation in a mouse model. Therefore, to what extent this gene cluster contributes to the spread and ecological specialisation of ICE-carrying hospital-associated isolates remains to be investigated.