Bacterial Identification Using PCR in a Large Series of Acute Post–Cataract Endophthalmitis

Abstract

Purpose: : To improve identification and speciation of bacteria involved in acute endophthalmitis after cataract surgery, using polymerase chain reaction (PCR) technique

Methods: : This prospective and multicenter study (2004 – 2005) includes, 82 patients (mean age 72 years, 1.7–96), with endophthalmitis after cataract surgery. In emergency, an anterior chamber puncture (n= 67) and/or a vitreous puncture (n= 23) was performed under aseptic conditions and was associated with intravitreal injection of antibiotics. Aqueous humor and/or vitreous samples are collected: 100 microL for standard culture (Brain Heart Infusion) and 150 microL for PCR. In 49 patients (60%) a posterior vitrectomy was performed 1–5 days after the first intravitreal injection of antibiotics and vitreous samples were analysed using the same techniques

Results: : Microbiological diagnosis is performed on aqueus humor samples in 46% (PCR 35%, cultures 38%) and on vitreous samples in 65% (PCR 64%, cultures 43%). The analysis of the vitreous from vitrectomy shows that the identification of the bacteria was done in 65%, always with PCR (all cultures were negative). Considering aqueous humor and vitreous samples (puncture and vitrectomy), the infectious agent was identified in 66% of the cases. Bacteria were Gram positive in 96% out of the cases (coagulase negative micrococci 48%, S. Aureus 9%, Streptococcus 26%, Haemophilus 1.8%, Proteus 1.8%). A coinfection with two bacteria is reported in 2 cases. The correlation between both techniques is excellent

Conclusions: : In acute endophthalmitis after cataract surgery, this large series shows a higher proportion of Gram positive bacteria than previously reported. In this selective population , the association of culture and PCR improves the identification of the causative pathogens in the vitreous from biopsy or vitrectomy. These preliminary results also suggest that PCR, such as cultures, performed on vitreous samples allow a higher rate of bacterial identification than on aqueous humor samples

Keywords: endophthalmitis • clinical laboratory testing