Novel Duplex Polymerase Chain Reaction for the Rapid Detection of Pythium insidiosum Directly From Corneal Specimens of Patients With Ocular Pythiosis.

Abstract

To standardize a novel duplex polymerase chain reaction (PCR) targeting 18S rRNA gene and internal transcribed spacer region for the identification of Pythium insidiosum isolates and also to detect P. insidiosum genome directly from corneal specimens of patients with suspected ocular pythiosis. A total of 42 nonsporulating molds culturally and morphologically resembling suspected unidentified fungal isolates (corneal buttons 33 and corneal scrapings 9) and 14 clinical specimens (corneal buttons 7 and corneal scrapings 7) clinically suspected to be ocular pythiosis were included in the present study. Standardization of uniplex PCRs and duplex PCRs targeting 18S rRNA gene and internal transcribed spacer region and further application of the standardized PCRs on both clinical isolates and clinical specimens suspected to have fungal keratitis. The sensitivity and specificity of the standardized duplex PCR were calculated using Medcal.net software. The standardized uniplex and duplex PCRs were found specific for the detection of only P. insidiosum DNA, and the analytical sensitivities of the primers were 1.36 Zg. Of the 14 clinical specimens analyzed, 13 were positive in both corneal specimens and their respective P. insidiosum isolates. The specificity of the novel duplex PCR was 100% when applied on corneal specimens and clinical isolates, but the sensitivity was 92.8% (13/14) and 100% (42/42), respectively, for the clinical specimens and fungal isolates from suspected ocular pythiosis patients included in the study. The novel duplex PCR developed in this study will aid in rapid identification of P. insidiosum clinical isolates and clinical specimens from suspected ocular pythiosis specimens, which in turn will help the ophthalmologists to initiate appropriate treatment.