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Infection and Immunity, September 2000, p. 5210-5217, Vol. 68, No. 9
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

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

Sreedhar R. Nallapareddy,1,2 Kavindra V. Singh,1,2 Ruay-Wang Duh,1,2,dagger George M. Weinstock,2,3 and Barbara E. Murray1,2,3,*

Division of Infectious Diseases, Department of Internal Medicine,1 Center for the Study of Emerging and Re-emerging Pathogens,2 and Department of Microbiology and Molecular Genetics,3 University of Texas Medical School, Houston, Texas 77030

Received 10 April 2000/Returned for modification 12 May 2000/Accepted 16 June 2000

Our previous work reported that most Enterococcus faecalis strains adhered to the extracellular matrix proteins collagen types I and IV and laminin after growth at 46°C, but not 37°C, and we subsequently identified an E. faecalis sequence, ace, that encodes a bacterial adhesin similar to the collagen binding protein Cna of Staphylococcus aureus. In this study, we examined the diversity of E. faecalis-specific ace gene sequences among 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 conserved 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-amino-acid partial repeat. Using 17 other strains collected worldwide, the 5' region of ace that encodes the A domain was sequenced, and these sequences showed >= 97.5% identity. Among the previously reported five amino acids critical for collagen binding by Cna of S. aureus, four were found to be identical in Ace from all strains tested. Polyclonal immune rabbit serum prepared against recombinant Ace A derived from E. faecalis strain OG1RF detected Ace in mutanolysin extracts of seven of nine E. faecalis strains after growth at 46°C; Ace was detected in four different 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 produced under physiological conditions, we quantitatively assayed sera collected from patients with enterococcal infections for the presence of anti-Ace A antibodies. Ninety percent of sera (19 of 21) from patients with E. faecalis endocarditis showed reactivity with titers from 1:32 to >1:1,024; the only 2 sera which lacked antibodies to Ace A had considerably lower titers of antibodies to other E. faecalis antigens as well. Human-derived, anti-Ace A immunoglobulins G purified from an E. faecalis endocarditis patient serum inhibited adherence of 46°C-grown E. faecalis OG1RF to collagen types I and IV and laminin. In conclusion, these results show that ace is highly conserved among isolates of E. faecalis, with at least four variants related to the differences in the B domain, is expressed by different strains during infection in humans, and human-derived antibodies can block adherence to these extracellular matrix proteins.

* Corresponding author. Mailing address: Center for the Study of Emerging and Re-emerging Pathogens, Division of Infectious Diseases, Department of Internal Medicine, University of Texas Medical School at Houston, 6431 Fannin St., Houston, TX 77030. Phone: (713) 500-6767. Fax: (713) 500-5495. E-mail: infdis{at}heart.med.uth.tmc.edu.

dagger Present address: Section of Infectious Diseases, Department of Medicine, Veterans General Hospital---Taipei, Taipei, Taiwan, Republic of China.

Infection and Immunity, September 2000, p. 5210-5217, Vol. 68, No. 9
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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