Fil: Albornoz, Ezequiel. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Servicio Antimicrobianos. Departamento de Bacteriología; Argentina.Fil: Lucero, Celeste. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Servicio Antimicrobianos. Departamento de Bacteriología; Argentina.Fil: Romero, Genara. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Servicio Antimicrobianos. Departamento de Bacteriología; Argentina.Fil: Quiroga, María Paula. Instituto de Investigaciones en Microbiología y Parasitología Médica, Universidad de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Tecnológicas (IMPaM, UBA-CONICET) , Ciudad Autónoma de Buenos Aires; Argentina.Fil: Rapoport, Melina. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Servicio Antimicrobianos. Departamento de Bacteriología; Argentina.Fil: Guerriero, Leonor. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Servicio Antimicrobianos. Departamento de Bacteriología; Argentina.Fil: Andres, Patricia. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Servicio Antimicrobianos. Departamento de Bacteriología; Argentina.Fil: Rodriguez, Cecilia. Instituto de Investigaciones en Microbiología y Parasitología Médica, Universidad de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Tecnológicas (IMPaM, UBA-CONICET) , Ciudad Autónoma de Buenos Aires; Argentina.Fil: Galas, Marcelo. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Departamento de Bacteriología; Argentina.Fil: Centrón, Daniela. Instituto de Investigaciones en Microbiología y Parasitología Médica, Universidad de Buenos Aires-Consejo Nacional de Investigaciones Científicas y Tecnológicas (IMPaM, UBA-CONICET) , Ciudad Autónoma de Buenos Aires; Argentina.Fil: Corso, Alejandra. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Servicio Antimicrobianos. Departamento de Bacteriología; Argentina.Fil: Petroni, Alejandro. ANLIS Dr.C.G.Malbrán. Instituto Nacional de Enfermedades Infecciosas. Servicio Antimicrobianos. Departamento de Bacteriología; Argentina.This first nationwide study was conducted to analyze the prevalence of plasmid-mediated quinolone resistance (PMQR) genes in phenotypically unselected (consecutive) clinical enterobacteria. We studied 1,058 isolates that had been consecutively collected in 66 hospitals of the WHONET-Argentina Resistance Surveillance Network. Overall, 26% of isolates were nonsusceptible to at least one of the three quinolones tested (nalidixic acid, ciprofloxacin, and levofloxacin). The overall prevalence of PMQR genes was 8.1% (4.6% for aac(6')-Ib-cr; 3.9% for qnr genes; and 0.4% for oqxA and oqxB, which were not previously reported in enterobacteria other than Klebsiella spp. from Argentina). The PMQR prevalence was highly variable among the enterobacterial species or when the different genes were considered. The prevalent PMQR genes were located in class 1 integrons [qnrB2, qnrB10, and aac(6')-Ib-cr]; in the ColE1-type plasmid pPAB19-1 or Tn2012-like transposons (qnrB19); and in Tn6238 or bracketed by IS26 and blaOXA-1 [aac(6')-Ib-cr]. The mutations associated with quinolone resistance that were located in the quinolone resistance-determining region (QRDR mutations) of gyrA, parC, and gyrB were also investigated. The occurrence of QRDR mutations was significantly associated with the presence of PMQR genes: At least one QRDR mutation was present in 82% of the PMQR-harboring isolates but in only 23% of those without PMQR genes (p < 0.0001, Fisher's Test). To the best of our knowledge, this is the first report on the prevalence of PMQR genes in consecutive clinical enterobacteria where all the genes currently known have been screened.