Diversity of ace, a gene encoding a microbial surface component recognizing adhesive matrix molecules, from different strains of Enterococcus faecalis and evidence for production of ace during human infections

Our previous work reported that most Enterococcus faecalis strains adhered to the extracellular matrix proteins collagen types I and IV and laminin af ter growth at 46 degrees C, but not 37 degrees C, and we subsequently ident ified an E. faecalis sequence, ace, that encodes a bacterial adhesin simila r to the collagen binding protein Cna of Staphylococcus aureus. In this stu dy, we examined the diversity of E. faecalis-specific ace gene sequences am ong different isolates obtained from various geographic regions as well as from various clinical sources. A comparison of nucleotide and deduced amino acid sequences of Ace from nine E. faecalis strains identified a highly co nserved N-terminal A domain, followed by a variable B domain which contains two to five repeats of 47 amino acids in tandem array, preceded by a 20-am ino-acid partial repeat. Using 17 other strains collected worldwide, the 5' region of ace that encodes the ii domain was sequenced, and these sequence s showed greater than or equal to 97.5% identity. Among the previously repo rted five amino acids critical for collagen binding by Cna of S. aureus, fo ur were found to be identical in Ace from an strains tested. Polyclonal imm une rabbit serum prepared against recombinant Ace A derived from E. faecali s strain OG1RF detected Ace in mutanolysin extracts of seven of nine E. fae calis strains after growth at 46 degrees C; Ace was detected in four differ ent molecular sizes that correspond to the variation in the B repeat region . To determine if there was any evidence to indicate that Ace might be prod uced under physiological conditions, we quantitatively assayed sera collect ed from patients with enterococcal infections for the presence of anti-Ace A antibodies. Ninety percent of sera (19 of 21) from patients with E. faeca lis endocarditis showed reactivity with titers from 1:32 to >1:1,024; the o nly 2 sera which lacked antibodies to Ace A had considerably tower titers o f antibodies to other E. faecalis antigens as well. Human-derived, anti-Ace A immunoglobulins G purified from an E. faecalis endocarditis patient seru m inhibited adherence of 46 degrees C-grown E. faecalis OG1RF to collagen t ypes I and IV and laminin. In conclusion, these results show that ace is hi ghly conserved among isolates of E. faecalis, with at least four variants r elated to the differences in the B domain, is expressed by different strain s during infection in humans, and human-derived antibodies can block adhere nce to these extracellular matrix proteins.