Development of NASBA®, a nucleic acid amplification system, for identification of Listeria monocytogenes and comparison to ELISA and a modified FDA method

NASBA®, an isothermal nucleic acid amplification system was used for identification of Listeria monocytogenes. A primer set and a species-specific probe were selected from the 16S rRNA sequence. The probe was shown to hybridize specifically to the amplifiied single-stranded RNA of L. monocytogenes. No hybridization occured with amplification product of L. seeligeri, L. innocua, L. ivanovii, and L. welshimeri. Detection sensitivity for the NASBA® assay was determined at 106cfuml. The possibility of using the NASBA® assay for detection of L. monocytogenes in foods after a 2-day enrichment procedure was explored. NASBA® was compared to a modified FDA method and ELISA for detection of L. monocytogenes artificially inoculated (1–100 cfu/25 g) in eight food products. False-negative results were obtained with the modified FDA method (6.75%). NASBA® and ELISA were shown in this study to detect the pathogen with equal efficiency (no false negative or false positive results). Both methods allowed detection of less than 10 cfu/25 g within 3 days but ELISA can only be used for diagnosis of Listeria spp. while the NASBA® procedure permitted specific identification of the human pathogen L. monocytogenes.