Use of polymerase chain reaction (PCR) and DNA probe hybridization to determine the gram reaction of the infecting bacterium in the intraocular fluids of patients with endophthalmitis

Objectives: To evaluate polymerase chain reaction (PCR) combined with DNA probe hybridization to determine the Gram reaction of the bacterium in intraocular specimens from patients with infectious endophthalmitis. Methods: Fifty-seven intraocular specimens - 17 aqueous humor (AH) and 40 vitreous fluid (VF) - from 55 patients with clinically diagnosed infectious endophthalmitis and 25 control intraocular specimens from non-infectious ocular disorders (10 BH and 15 VF) were evaluated by microscopy, culture and PCR-DNA probe hybridization to detect the Gram reaction of the bacterium. Results: PCR-DNA probe hybridization was specific and sensitive to detect 30 fg of both Gram-positive and Gramnegative bacterial DNA. None of the controls showed bacteria by microscopy, culture or PCR. Of the 57 intraocular specimens, conventional microbiological methods could detect a bacterial aetiology in 32 (56.1%), while PCR-DNA probe hybridization could detect 52 (91.2%) specimens. This difference was statistically significant (P=0.003). In bacteriologically positive specimens, there was absolute correlation of the Gram reaction between the results of smear and culture methods and PCR-DNA probe hybridization. Of the 25 bacteriologically negative specimens, 20 (80%) were positive by PCR-DNA probe hybridization, of which seven (35%) were Gram-positive, 12 (60%) Gram-negative and one (5%) positive by both. Results of PCR on AH and VF were not significantly different. Conclusion: PCR and DNA probe hybridization to determine the Gram reaction of the bacterium in intraocular fluids is a specific and sensitive method in the diagnosis of bacterial endophthalmitis. AH is an ideal specimen for PCR, since its collection is a simple and safe office procedure. (C) 2000 The British Infection Society.