Application of Polymerase Chain Reaction (PCR) In the diagnosis of neurocryptoccosis

In the last two decades, cryptococcosis has been gaining a distinct public health importance due to the growing number of AIDS cases. Considering the low sensitivity of direct examination with India ink and culture, use of sensitive techniques is crucial in the diagnosis of cryptococcal meningitis. Polymerase Chain Reaction (PCR) can be used to directly detect Cryptococcus neoformans in CSF samples to increase the diagnostic power in cases where conventional methods are unable to detect the organism.

In this cross-sectional study, CSF samples were obtained from 25 patients suspected of having neurocryptococcosis. The patients were referred to the Medical Mycology Laboratory of the School of Public Health affiliated to Tehran University of Medical Sciences from March 2009 to February 2010. Three different methods, direct India ink examination, culture and PCR were used to evaluate the CSF samples. Two 102 and 106 of Cryptococcus neoformans dilutions in 1ml of CSF were prepared and examined by the three methods. In PCR method, two primer pairs were selected to amplify the Cryptococcus neoformans URA5 gene. The sequences of primers were for A, B, C and D serotypes.

Only in one case PCR, as well as direct examination and culture were positive. All the other samples were negative in PCR, direct examination or culture. Both CSF dilutions were positive in the three tests in the mentioned patient and the positive control.

PCR method can efficiently identify both control and positive samples of Cryptococcus neoformans.