Detection of Nocardia Asteroides Complex in Clinical Isolates by Real-Time Polymerase Chain Reaction

Nocardia asteroides complex is the most common cause of infectious diseases due to nocardiosis. Interspecies differentiation of Nocardia genera is essential for prognosis and timely proper treatment, as well as for epidemiological studies. Since each genus has its own antibiotic resistance, precise careful diagnosis is of prime importance. As compared to biochemical and phenotypic methods, the efficacy of molecular methods for fast and accurate identification of Nocardia species has been proven. The aim of this study was to detect for the first time Nocardia asteroides complex in clinical isolates using real time polymerase chain reaction (Real-Time PCR).

Out of the 25 clinical isolates suspected to be Nocardia asteroides genus 10 were identified as Nocardia asteroids complex by biochemical and phenotypic methods, followed by genomic DNA extraction of the suspicious isolates. Nocardia asteroides complex positive controls were prepared using standard strains. Real-time PCR was conducted on all the 10 suspicious isolates. The final real-time PCR samples were sent for sequencing to verify the identified species.

Based on sequencing results 3 of 10 clinical isolates suspected to be identified as Nocardia asteroides complex were confirmed as belonging to the Nocardia asteroids complex genera ─ Nocardia asteroids, Nocardia farcinica, and Nocardia nova.

This study shows that, as compared to biochemical and phenotypic methods, real-time polymerase chain reaction is faster and more specific, and is considered as an efficient method, for Nocardia interspecies identification and differentiation.