The source of coagulase-negative staphylococci in the endophthalmitis vitrectomy study - A comparison of eyelid and intraocular isolates using pulsed-field gel electrophoresis

Objective: To determine the species distribution of coagulase-negative staphylococci (CoNS) inpatients with endophthalmitis and to ascertain whether the patient's own flora was a major source of postoperative endophthalmitis following cataract extraction. Methods: In a 4-year multicenter prospective study, 524 bacterial isolates were submitted from 225 Endophthalmitis Vitrectomy Study patients. From the 524 isolates, 250 represented CoNS cultured from the anterior chamber, the vitreous, or both of the 225 patients. Where possible, paired isolates from an individual patient's eyelid and intraocular compartment(s) were studied by pulsed-field gel electrophoresis, an established molecular strain-typing technique. Results: From all sites the most frequently isolated CoNS were Staphylococcus epidermidis (81.9%) and Staphylococcus lugdunensis (5.9%). Where analysis was possible, eyelid isolates were indistinguishable from intraocular isolates in 71 (67.7%) of 105 comparisons. Non-S epidermidis CoNS caused postoperative endophthalmitis in 5 patients. Four of the 5 had postoperative endophthalmitis caused by S lugdunensis and 1 by Staphylococcus haemolyticus. Conclusions: Coagulase-negative staphylococci from the patient's periocular skin flora play a significant role in causing intraocular infections, and non-S epidermidis CoNS play a small but significant role. These results reinforce the necessity to follow stringent surgical site preparation prior to eye surgery.