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1 December 2008 Molecular Characterization and Typing of Enrofloxacin-Resistant Clinical Isolates of Mycoplasma gallisepticum
I. Lysnyansky, I. Gerchman, S. Perk, S. Levisohn
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Emergence of resistance to fluoroquinolones is mainly due to chromosomal mutations in genes encoding the subunits of the drug's target enzymes, DNA gyrase and topoisomerase IV, which are essential for DNA replication. The quinolone resistance-determining regions (QRDRs) of these genes were characterized in 25 Mycoplasma gallisepticum strains isolated from commercial poultry flocks during 1997–2007, which exhibited different levels of susceptibility to fluoroquinolones. All enrofloxacin-resistant isolates harbored amino acid substitutions in the QRDRs of each of three proteins (GyrA, GyrB, and ParC). Molecular typing of those strains by random amplification of polymorphic DNA and gene-targeted sequencing supports ongoing, stepwise selection of resistant strains from the existing reservoir of susceptible M. gallisepticum strains.

Abbreviations: aa = amino acid; B = broiler chicken; BB = broiler breeder chicken; GTS = gene-targeted sequencing; LB = leghorn-type breeder chicken; MIC = minimal inhibitory concentration; MT = Meat-type turkey; NCCLS = National Committee for Clinical Laboratory Standards; nt = nucleotide; PCR = polymerase chain reaction; QRDR = quinolone resistance-determining region; RAPD = random amplification of polymorphic DNA

Nota de Investigación—Caracterización molecular y tipificación de aislamientos clínicos de Mycoplasma gallisepticum resistentes a la Enrofloxacina.

La aparición de resistencia a la fluoroquinolonas se debe principalmente a mutaciones de los cromosomas en genes que codifican las subunidades de las enzimas blanco de la droga, la ADN girasa y la topoisomerasa IV, que son esenciales para la replicación del ADN. Se caracterizaron las regiones determinantes de resistencia a la quinolona de estos genes en 25 cepas de Mycoplasma gallisepticum aisladas de parvadas comerciales de aves domésticas durante los años 1997 al 2007 que mostraban diferentes niveles de susceptibilidad a las fluoroquinolonas. Todos los aislamientos resistentes a la enrofloxacina mostraron substituciones de aminoácidos en las regiones determinantes de resistencia a la quinolona de cada una de tres proteínas (GyrA, GyrB, y ParC). La tipificación molecular de estas cepas mediante amplificación aleatoria de ADN polimórfico y secuenciación directa de genes, apoyan la selección activa y constante de cepas resistentes a partir del reservorio de cepas susceptibles de M. gallisepticum.

I. Lysnyansky, I. Gerchman, S. Perk, and S. Levisohn "Molecular Characterization and Typing of Enrofloxacin-Resistant Clinical Isolates of Mycoplasma gallisepticum," Avian Diseases 52(4), 685-689, (1 December 2008).
Received: 2 July 2008; Accepted: 1 August 2008; Published: 1 December 2008

molecular typing
Mycoplasma gallisepticum
quinolone resistance-determining regions
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