CONICET | Buscador de Institutos y Recursos Humanos

Background The genus Enterococcus is a diverse group of low GC% gram-positive bacteria that contains over 33 species. The genera include commensal, environmental but also opportunistic human pathogens such E. faecalis and E. faecium. Enterococcus mundtii is a yellow-pigmented microorganism rarely found in human infections. Specifically, E. mundtii CRL1656 strain has been proposed as a probiotic microorganism to prevent mastitis in cows [1]. This strain was isolated from stripping milk of an Argentinean cow and its genome was recently sequenced [2]. The aim of this study was to gain insights into the similarities in the genetic content of E. mundtii with respect to other enterococcal species and, more specifically, to investigate on the genes coding for virulence factors shared with enterococcal opportunistic pathogens. Materials and methods Assignment of E. mundtii CRL1656 putative gene products were performed using RAST and the depurated E. faecalis V583 genome sequence as reference. Comparative genome analysis against other enterococcal species was performed using the same tool. Unique genes were determined by using RAST Compare Metabolic Reconstruction tool and BLAST and tBLASTn. To detect putative Genome Islands (GEIs), Alien-Hunter, Colombo/SIGI-HMM and/or IslandPath-DIMOB were used as first identification criterion. Then, we use Artemis and DNAplotter to find out further evidences related to GEIs, in general, and Pathogenic Island (PAIs), in particular. Finally, BlastP analysis of enterococcal proteomes were made against MvirDB, a Virulence Factors Database. Results This study is the first comparative analysis of E. mundtii genome against the complete genomic sequences of other enterococcal species. E. mundtii CRL1656 genome encodes at least 2,589 genes and 57 RNAs, and 4 putative genomic islands have been identified. Bioinformatic analysis revealed an enterococcal gene core of 827 CDS inferred by comparison between E. mundtii, E. faecalis, E. faecium, E. saccharolyticus, E. italicus, E. gallinarum and E. casseliflavus genomes. Although E. mundtii CRL1656 is phylogenetically closer to E. faecalis and E. faecium, both responsible of most nosocomial infections, this strain does not encode the most relevant virulence factors found in the enterococcal clinical isolates and posses the lowest number of putative pathogenic genes among the most representative enterococcal species. The general features of the genome are summarized in Figure 1. Figure 1: Circular representation of E. mundtii genome. Protein-coding genes on both strands (light blue). Foreign DNA as predicted by Alien Hunter (red), Columbo Sigi (grey) and IslandPath-DIMOB (green). tRNA (black), tranposase (blue), and integrase (ochre) genes. Regions above (yellow) and less than or equal to the median G+C% (violet). Circular sectors I-IV highlight the position of putative genomic islands. Conclusions Our study reveals significant similarities in the physiology of E. mundtii with the selected strains of enterococci, which contributes to understand the persistence of this genus in different niches and also improves our understanding of the genetics of this diverse group of microorganisms that includes environmental, commensal and pathogenic bacteria. Further investigation is needed to determine the safety of E. mundtii CRL1656 for its use as probiotic. Reference [1] Espeche MC, Otero MC, Sesma F, Nader-Macias ME: Screening of surface properties and antagonistic substances production by lactic acid bacteria isolated from the mammary gland of healthy and mastitic cows. Vet Microbiol 2009,135:346-357 [2] Magni, C. et al: Draft genome sequence of Enterococcus mundtii CRL1656. J Bacteriol 2012, 194:550.