Genomic and phenotypic diversity of Enterococcus faecalis isolated from endophthalmitis

Abstract

Enterococcus faecalis are hospital-associated opportunistic pathogens and also causative agents of post-operative endophthalmitis. Patients with enterococcal endophthalmitis often have poor visual outcomes, despite appropriate antibiotic therapy. Here we investigated the genomic and phenotypic characteristics of E. faecalis isolates collected from 13 patients treated at the University of Pittsburgh Medical Center Eye Center over 19 years. Comparative genomic analysis indicated that patients were infected with E. faecalis of diverse multi-locus sequence types (STs) previously associated with clinical, commensal, and environmental sources. We identified known E. faecalis virulence factors and antibiotic resistance genes in each genome, including genes conferring resistance to aminoglycosides, erythromycin, and tetracyclines. We assessed all isolates for their cytolysin production, biofilm formation, and antibiotic susceptibility, and observed phenotypic differences between isolates. Fluoroquinolone and cephalosporin susceptibilities were particularly variable, as were biofilm formation and cytolysin production. In addition, we found evidence of E. faecalis adaptation during recurrent endophthalmitis by identifying genetic variants that arose in sequential isolates sampled over eight-months from the same patient. We identified a mutation in the DNA mismatch repair gene mutS that was associated with a hypermutator phenotype in the final isolate from the patient, which was also more resistant to ceftazidime. Overall this study documents the genomic and phenotypic variability among E. faecalis causing endophthalmitis, as well as possible adaptive mechanisms underlying bacterial persistence during recurrent ocular infection. IMPORTANCEBacterial endophthalmitis is a sight-threatening infection of the inside of the eye. Enterococcus faecalis cause endophthalmitis occasionally, but when they do the infections are often severe. Here we investigated the genomes, antibiotic susceptibilities, and virulence-associated traits among E. faecalis collected from 13 patients with post-operative endophthalmitis. We wondered whether there were common bacterial factors that might explain why enterococcal endophthalmitis is so destructive to ocular tissues. Instead we found that E. feacalis isolated from endophthalmitis were genetically and phenotypically diverse; isolates belonged to a variety of genetic lineages and showed varying levels of antibiotic resistance and biofilm formation. We also undertook further characterization of three closely related E. faecalis isolates from a patient with recurrent endophthalmitis, and found that a hypermutator strain emerged during persistent infection. Hypermutators have been found in a variety of other infection contexts; here we describe what we believe is the first case of a hypermutator arising during ocular infection.