| Summary: | Alma López-García,1 Rosa del Carmen Rocha-Gracia,1 Elena Bello-López,1 Claudia Juárez-Zelocualtecalt,1 Yolanda Sáenz,2 Miguel Castañeda-Lucio,1 Liliana López-Pliego,1 María Cristina González-Vázquez,1 Carmen Torres,3 Teolincacihuatl Ayala-Nuñez,1 Guadalupe Jiménez-Flores,4 Margarita María de la Paz Arenas-Hernández,1 Patricia Lozano-Zarain1 1Benemérita Universidad Autónoma de Puebla, Instituto de Ciencias, Posgrado en Microbiología, Centro de Investigaciones en Ciencias Microbiológicas, Complejo de Ciencias, Ciudad Universitaria. Col San Manuel CP, Puebla, Mexico; 2Area de Microbiología Molecular, Centro de Investigación Biomédica de La Rioja (CIBIR), Logroño, Spain; 3Area Bioquímica y Biología Molecular, Universidad de La Rioja, Logroño, Spain; 4Laboratorio de Análisis Clínicos, Sección de Microbiología, Hospital Regional Instituto de Seguridad y Servicios Sociales de los Trabajadores del Estado, Puebla, Mexico Purpose: Pseudomonas aeruginosa infections in hospitals constitute an important problem due to the increasing multidrug resistance (MDR) and carbapenems resistance. The knowledge of resistance mechanisms in Pseudomonas strains is an important issue for an adequate antimicrobial treatment. Therefore, the objective was to investigate other antimicrobial resistance mechanisms in MDR P. aeruginosa strains carrying blaIMP, make a partial plasmids characterization, and determine if modifications in oprD gene affect the expression of the OprD protein. Methodology: Susceptibility testing was performed by Kirby Baüer and by Minimum Inhibitory Concentration (presence/absence of efflux pump inhibitor); molecular typing by Pulsed-field gel electrophoresis (PFGE), resistance genotyping and integrons by PCR and sequencing; OprD expression by Western blot; plasmid characterization by MOB Typing Technique, molecular size by PFGE-S1; and blaIMP location by Southern blot. Results: Among the 59 studied P. aeruginosa isolates, 41 multidrug resistance and carbapenems resistance isolates were detected and classified in 38 different PFGE patterns. Thirteen strains carried blaIMP; 16 blaGES and four carried both genes. This study centered on the 17 strains harboring blaIMP. New variants of β-lactamases were identified (blaGES-32, blaIMP-56, blaIMP-62) inside of new arrangements of class 1 integrons. The presence of blaIMP gene was detected in two plasmids in the same strain. The participation of the OprD protein and efflux pumps in the resistance to carbapenems and quinolones is shown. No expression of the porin OprD due to stop codon or IS in the gene was found. Conclusions: This study shows the participation of different resistance mechanisms, which are reflected in the levels of MIC to carbapenems. This is the first report of the presence of three new variants of β-lactamases inside of new arrangements of class 1 integrons, as well as the presence of two plasmids carrying blaIMP in the same P. aeruginosa strain isolated in a Mexican hospital. Keywords: Pseudomonas aeruginosa, resistance mechanisms, plasmid, integrons
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