Enterococcus faecium Biofilm Formation: Identification of Major Autolysin AtlA(Efm), Associated Acm Surface Localization, and AtlA(Efm)-Independent Extracellular DNA Release

Enterococcus faecium is an important multidrug-resistant nosocomial pathogen causing biofilm-mediated infections in patients with medical devices. Insight into E. faecium biofilm pathogenesis is pivotal for the development of new strategies to prevent and treat these infections. In several bacteria, a major autolysin is essential for extracellular DNA (eDNA) release in the biofilm matrix, contributing to biofilm attachment and stability. In this study, we identified and functionally characterized the major autolysin of E. faecium E1162 by a bioinformatic genome screen followed by insertional gene disruption of six putative autolysin genes. Insertional inactivation of locus tag EfmE1162_2692 resulted in resistance to lysis, reduced eDNA release, deficient cell attachment, decreased biofilm, decreased cell wall hydrolysis, and significant chaining compared to that of the wild type. Therefore, locus tag EfmE1162_2692 was considered the major autolysin in E. faecium and renamed atlA(Efm). In addition, AtlA(Efm) was implicated in cell surface exposure of Acm, a virulence factor in E. faecium, and thereby facilitates binding to collagen types I and IV. This is a novel feature of enterococcal autolysins not described previously. Furthermore, we identified (and localized) autolysin-independent DNA release in E. faecium that contributes to cell-cell interactions in the atlA(Efm) mutant and is important for cell separation. In conclusion, AtlA(Efm) is the major autolysin in E. faecium and contributes to biofilm stability and Acm localization, making AtlA(Efm) a promising target for treatment of E. faecium biofilm-mediated infections.