Novel method for rapid identification of Nocardia species by detection of preformed enzymes

Abstract

The purpose of the present study was to devise a method for the identification of Nocardia species that is more technically simple, accurate, and rapid than current standard methods of identification. We focused on a commercial bacteria identification system that contained chromogenic test substrates. Two MicroScan products were selected for use in the study on the basis of their content of chromogenic and conventional substrates. They were the Rapid Anaerobe Identification and the HNID panels. A total of 85 strains of Nocardia representing five species were used in the study. All isolates were identified as Nocardia species by the use of standard methods. The β-naphthylamide-labeled substrate L-pyrrolidonyl-β-naphthylamide (PYR), the nitrophenyl-labeled substrate-p-nitrophenyl-α-D-mannopyranoside (MNP), and indoxyl phosphate were found to be useful for identification purposes. N. farcinica and N. nova were the only species positive for PYR, whereas N. brasiliensis was the only species that hydrolyzed MNP. All strains of N. brasiliensis, N. otitidiscavarium, and N. farcinica were positive for indoxyl phosphate, whereas strains of N. nova and N. asteroides sensu stricto were always negative. Agreement between the standard and enzymatic identification methods was 100%. In summary, detection of preformed enzymes appears to be a simple and reproducible method for the identification of Nocardia spp.