Previously, we described a gene cluster of Enterococcus faecalis OG1RF that produced an antigenic polysaccharide when cloned in Escherichia coli. The polysaccharide antigen was not detectable in E. faecalis strains, however. Here, we show by reverse transcriptase-PCR that the 16 genes in this region are transcribed in OG1RF. Gene disruption of orfde4, encoding a putative glycosyl transferase, and orfde6, a putative dTDP-rhamnose biosynthesis gene, generated two OG1RF mutants. The mutants showed delayed killing and a higher 50% lethal dose in a mouse peritonitis model. In addition, two mucoid E. faecalis isolates from patients with chronic urinary tract infections were found to produce the polysaccharide antigen.