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Antimicrobial Agents and Chemotherapy, July 2005, p. 2928-2933, Vol. 49, No. 7
0066-4804/05/$08.00+0     doi:10.1128/AAC.49.7.2928-2933.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Evaluation of a New Line Probe Assay for Rapid Identification of gyrA Mutations in Mycobacterium tuberculosis

Federico Giannoni,^1, Elisabetta Iona,^1, Federica Sementilli,¹ Lara Brunori,¹ Manuela Pardini,¹ Giovanni Battista Migliori,² Graziella Orefici,¹ and Lanfranco Fattorini^1*

Dipartimento di Malattie Infettive, Parassitarie e Immunomediate, Istituto Superiore di Sanità, Rome,¹ WHO Collaborating Centre for the Control of Tuberculosis and Lung Diseases, Fondazione S. Maugeri, Tradate, Varese, Italy²

Received 12 November 2004/ Returned for modification 21 January 2005/ Accepted 3 March 2005

Resistance of Mycobacterium tuberculosis to fluoroquinolones (FQ) results mostly from mutations in the gyrA gene. We developed a reverse hybridization-based line probe assay in which oligonucleotide probes carrying the wild-type gyrA sequence, a serine-to-threonine (S95T) polymorphism, and gyrA mutations (A90V, A90V-S95T, S91P, S91P-S95T, D94A, D94N, D94G-S95T, D94H-S95T) were immobilized on nitrocellulose strips and hybridized with digoxigenin-labeled PCR products obtained from M. tuberculosis strains. When a mutated PCR product was used, hybridization occurred to the corresponding mutated probe but not to the wild-type probe. A panel of M. tuberculosis complex strains including 19 ofloxacin-resistant (OFL-R) and 9 ofloxacin-susceptible (OFL-S) M. tuberculosis strains was studied for detection and identification of gyrA mutations by the line probe assay and nucleotide sequencing, in comparison with testing of in vitro susceptibility to FQ. Results were 100% concordant with those of nucleotide sequencing. The S95T polymorphism, which is not related to FQ resistance, was found in 5 OFL-S and 2 OFL-R strains; the other 17 OFL-R strains harbored single mutations associated with serine or threonine at codon 95. No mutations were found in the other OFL-S strains. Overall, on the basis of the MICs on solid medium, the new line probe assay correctly identified all OFL-S and 17 out of 19 (89.5%) OFL-R strains. A nested-PCR protocol was also evaluated for the assay to amplify PCR products from M. tuberculosis-spiked sputa, with a good specificity and a sensitivity of 2 x 10³ M. tuberculosis CFU per ml of sputum.

The first two authors, F.G. and E.I., contributed equally to this work.

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