Genetic relatedness of Enterococcus faecalis between eye-associated isolates and the other clinical isolates

Abstract

Purpose: Enterococci are commensal bacteria of human intestine and known as a leading cause of nosocomial infection. They are rarely isolated from ocular samples including conjunctival swab, discharge and intraocular fluid of endophthalmitis. However, the origin of such ocular isolates is not known. We performed multilocus sequence typing (MLST) analysis against Enterococcus faecalis isolates from various source to know whether eye-associated strains belonged to specific phylogenetic clusters or not. Closely related strains by MLST were further investigated the clonality by pulsed-field gel electrophoresis (PFGE) and plasmid DNA analysis.

Methods: The 15 ocular isolates from conjunctival swabs, intraocular lenses removed from eyes with endophthalmitis and discharges from dry-eye patients and the 13 non-ocular clinical isolates from blood, throat swab, urine, vaginal discharge, feces and peritoneal fluid were used as bacterial strains. All strains were E. faecalis. Five housekeeping genes (gdh, gyd, pstS, gki, aroE) were amplified by PCR, sequenced and then applied to MLST analysis. The obtained nucleotide sequences were aligned and compared by using Clustal W program. A phylogenetic tree was constructed by the neighbor-joining method. PFGE and agarose gel electrophoresis of plasmid DNA were carried out against strains belonging the same sequence types (STs).

Results: MLST analysis revealed that the 28 E. faecalis strains were divided into 11 STs. The ocular isolates did not compose any specific genetic clusters. Several ocular strains were closely related with non-ocular clinical isolates. One of the dry-eye patient had retained the identical strain in her conjunctival sacs for about a year.

Conclusions: E. faecalis isolated from eyes were related with general clinical isolates. There were no eye-specific phylogenetic clusters. Ocular surfaces with dry-eye possibly retain E. faecalis for a long time.

Keywords: 433 bacterial disease • 513 endophthalmitis