Genetic and Phenotypic Traits of Staphylococcus Epidermidis Strains Causing Postcataract Endophthalmitis Compared to Commensal Conjunctival Flora.

Abstract

The aim of this study was to compare the virulence and antibiotic resistance traits of Staphylococcus epidermidis strains causing acute postcataract endophthalmitis to those isolated from the conjunctiva of uninfected control patients. Case-control study. We isolated an S epidermidis strain from each of the 22 endophthalmitis patients, and from 43 of the 72 controls. Species identification was confirmed using both Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry and tuf gene amplification and sequencing. Antibiotic susceptibilities were evaluated using the AST-P631 card and the Vitek II automated system. The S epidermidis strains were tested for the presence of 7 virulence genes (icaA, icaB, icaC, icaD, atlE, aap, and capA), the insertion sequence IS256, and the mecA gene. The S epidermidis strains from the endophthalmitis patients displayed higher prevalence rates for aap, atlE, and mecA gene carriage compared to those of the control group (77% vs 42%, P = .007; 100% vs 79%, P = .02; and 54% vs 11%, P < .001, respectively). They also harbored the combination of the mecA and icaA genes more frequently compared to the control group (13% vs 2%, P = .01). They were significantly more resistant than control strains to methicillin, fluoroquinolones, and the aminoglycosides. A higher capacity of adhesion to the intraocular lens and formation of biofilms as well as greater resistance to antibiotics were found in S epidermidis strains causing postcataract endophthalmitis. The usefulness of such virulence and antibiotic resistance markers warrants further evaluation for prevention, treatment, and prognostic evaluation of S epidermidis endophthalmitis.