Project description:The success of Enterococcus faecium and E. faecalis evolving as multi-resistant nosocomial pathogens is associated with their ability to acquire and share adaptive traits, including mobile genetic elements (MGE) encoding antimicrobial resistance. Here, we define the mobilome in representative successful hospital associated genetic lineages, E. faecium ST17 (n=10) and ST78 (n=10), E. faecalis ST6 (n=10) and ST40 (n=10) using DNA microarray analyses. The hybridization patterns of 272 targets representing plasmid backbones (n=85), transposable elements (n=85), resistance determinants (n=67), prophages (n=29), and CRISPR-cas sequences (n=6) separated the strains according to species, and for E. faecalis also according to STs. Although plasmids belonging to the RCR-, Rep_3-, RepA_N- and Inc18-families were well represented with no significant differences in prevalence, the presence of specific replicon classes differed highly between the species; E. faecium was dominated by rep17/pRUM, rep2/pRE25, rep14/EFNP1 and rep20/pLG1 and E. faecalis by rep9/pCF10, rep2/pRE25 and rep7. Tn916-elements conferring tetracycline resistance (tetM) were found in all E. faecalis strains, but only in two E. faecium strains. A significant higher prevalence of IS256-, IS3-, ISL3-, IS200/IS605-, IS110-, IS982-, and IS4-transposases were detected in E. faecium, and of IS110-, IS982- and IS1182-transposases in E. faecalis ST6 compared to ST40. Notably, the transposases of IS981, ISEfm1 and IS1678 which have only been reported in few enterococcal isolates, were well represented in the E. faecium strains. E. faecalis ST40 strains harboured possible functional CRISPR-Cas systems, and still resistance and prophage sequences were generally well represented. Gene targets defined as the enterococcal mobilome, including plasmids, IS elements and transposons, resistance determinants, prophage sequences and CRISPR-Cas systems were highly prevalent, underlining their potential importance in the evolution of hospital associated STs. An association between axe-txe to the RepA_N-family and ω-ε-ζ to the Inc18-family, implicates the contribution of TA-systems in stable plasmid maintenance carrying virulence and resistance determinants in enterococci. The concurrent presence of defined MGE and their associated resistance markers was generally confirmed and illustrates the importance of horizontal gene transfer in the development of multidrug resistant enterococci.

Project description:Enterococcus faecium clinical isolates A902 and BM4538, which were resistant to relatively high levels of vancomycin (128 and 64 microg/ml, respectively) and to low levels of teicoplanin (4 microg/ml), and Enterococcus faecalis clinical isolates BM4539 and BM4540, which were resistant to moderate levels of vancomycin (16 microg/ml) and susceptible to teicoplanin (0.25 microg/ml), were studied. They were constitutively resistant by synthesis of peptidoglycan precursors ending with d-alanyl-d-lactate and harbored a chromosomal vanD gene cluster which was not transferable by conjugation to other enterococci. VanX(D) activity, which is not required in the absence of d-Ala-d-Ala, was low in the four strains, although none of the conserved residues was mutated; and the constitutive VanY(D) activity in the membrane fractions was inhibited by penicillin G. The mutations E(13)G in the region of d-alanine:d-alanine ligase (which is implicated in d-Ala1 binding in A902) and S(319)N of the serine involved in ATP binding in BM4538 and a 7-bp insertion at different locations in BM4539 and BM4540 (which led to putative truncated proteins) led to the production of an impaired enzyme and accounted for the lack of d-Ala-d-Ala-containing peptidoglycan precursors. The same 7-bp insertion in vanS(D) of BM4539 and BM4540 and a 1-bp deletion in vanS(D) of A902, which in each case led to a putative truncated and presumably nonfunctional protein, could account for the constitutive resistance. Strain BM4538, with a functional VanS(D), had a G(140)E mutation in VanR(D) that could be responsible for constitutive glycopeptide resistance. This would represent the first example of constitutive van gene expression due to a mutation in the structural gene for a VanR transcriptional activator. Study of these four additional strains that could be distinguished on the basis of their various assortments of mutations confirmed that all VanD-type strains isolated so far have mutations in the ddl housekeeping gene and in the acquired vanS(D) or vanR(D) gene that lead to constitutive resistance to vancomycin.

Project description:Enterococci are among the leading causes of hospital-acquired infections in the United States and Europe, with Enterococcus faecalis and Enterococcus faecium being the two most common species isolated from enterococcal infections. In the last decade, the proportion of enterococcal infections caused by E. faecium has steadily increased compared to other Enterococcus species. Although the underlying mechanism for the gradual replacement of E. faecalis by E. faecium in the hospital environment is not yet understood, many studies using genotyping and phylogenetic analysis have shown the emergence of a globally dispersed polyclonal subcluster of E. faecium strains in clinical environments. Systematic study of the molecular epidemiology and pathogenesis of E. faecium has been hindered by the lack of closed, complete E. faecium genomes that can be used as references.In this study, we report the complete genome sequence of the E. faecium strain TX16, also known as DO, which belongs to multilocus sequence type (ST) 18, and was the first E. faecium strain ever sequenced. Whole genome comparison of the TX16 genome with 21 E. faecium draft genomes confirmed that most clinical, outbreak, and hospital-associated (HA) strains (including STs 16, 17, 18, and 78), in addition to strains of non-hospital origin, group in the same clade (referred to as the HA clade) and are evolutionally considerably more closely related to each other by phylogenetic and gene content similarity analyses than to isolates in the community-associated (CA) clade with approximately a 3-4% average nucleotide sequence difference between the two clades at the core genome level. Our study also revealed that many genomic loci in the TX16 genome are unique to the HA clade. 380 ORFs in TX16 are HA-clade specific and antibiotic resistance genes are enriched in HA-clade strains. Mobile elements such as IS16 and transposons were also found almost exclusively in HA strains, as previously reported.Our findings along with other studies show that HA clonal lineages harbor specific genetic elements as well as sequence differences in the core genome which may confer selection advantages over the more heterogeneous CA E. faecium isolates. Which of these differences are important for the success of specific E. faecium lineages in the hospital environment remain(s) to be determined.

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Enterococcus faecium D344SRF

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