Characterisation of carbapenem-resistance mechanisms in clinical Pseudomonas aeruginosa isolates recovered in a Spanish hospital

Abstract Introduction Carbapenems are the beta-lactam antibiotics with the best spectrum of activity in the treatment of Pseudomonas aeruginosa infections. The objective of this study was to molecularly characterise a collection of carbapenem-resistant P. aeruginosa isolates (PARC). Methods A total of 85 PARC isolates were recovered from 60 patients in the Hospital San Pedro, Logrono (period 2008–2011). Clonal relationship was determined using pulsed-field gel electrophoresis (PFGE), susceptibility testing to 15 anti-pseudomonal agents was performed using the disk diffusion method, and alterations in oprD , characterisation of integrons and molecular typing (MLST) using PCR and sequencing. Results The 85 PARC were classified into 35 different PFGE profiles. Of the 61 selected strains from 60 patients all of them were multiresistant, although none of them showed a carbapenemase phenotype. High polymorphism was detected in OprD, emphasising that 59% of the strains had a premature stop codon. IS Pa1328 and IS Psp4 insertion sequences truncated oprD gene into 2 strains (GenBank KF517097 and KF517098). Two-thirds (67%) of the strains showed class 1 integrons with genes encoding aminoglycoside modifying enzymes, and 2 of them carried a new integron: aac (3)-Ia+ aadA1h , named In272, GenBank GQ144317. Four sequence types were detected (Strain Nos.): ST175 (35), ST308 (3), ST235 (2), and ST639 (1). Conclusion Multidrug resistance, high polymorphism in oprD , a high percentage of integrons, moderate clonal relationship of strains, and the high epidemic dissemination of high-risk clones are clinical aspects of great concern in order to eradicate the spread of PARC.