Carbapenem-resistant Pseudomonas aeruginosa strains from a Spanish hospital: characterization of metallo-beta-lactamases, porin OprD and integrons

Abstract

Molecular typing and mechanisms of carbapenem resistance such as alterations in porin OprD and presence of metallo-beta-lactamases (MBLs), as well as integrons have been studied in a collection of carbapenem-resistant Pseudomonas aeruginosa (CRPA) isolates from a Spanish hospital. One hundred and twenty-three CRPA isolates were recovered from different samples of 80 patients. Clonal relationship among CRPA was analyzed by SpeI-PFGE. Susceptibility testing to 11 antibiotics and MBL phenotype was determined by microdilution, IP/IPI E-test and double disc method. The oprD gene was studied by PCR and sequencing, and mutations were determined comparing with P. aeruginosa PAO1 sequence. Characterization of MBLs, and class 1 and 2 integrons were studied by PCR and sequencing. SDS-PAGE analysis of outer membrane proteins of selected strains was performed. Seventy-four-per-cent of patients with CRPA were hospitalised in the ICU setting and 50% had long hospitalization stays. Sixty-four different PFGE patterns were detected, and 87 CRPA strains were further analyzed. MBL phenotype was detected in 43 of 87 strains (49.4%), which contained blaVIM-2 gene inside class 1 integrons. VIM-2-producing strains belonged to lineages ST175, ST235, and ST973. A great diversity of nucleotide insertions, deletions, and mutations in oprD gene, and the presence of a new insertion sequence (ISPa45) truncating oprD were identified among CRPA strains. Class 1 integrons were detected in 75% of CRPA strains, blaVIM-2 and the new arrangement aac(3)-Ia+ISPa34+aadA1 (named as In661) being the most frequent gene-cassette arrays detected. Other gene cassettes detected in integrons were: aadB, aadA6, aadA7, aac(6')-Ib', and blaOXA-46.

Keywords: Carbapenem resistance; ISPa45; ST175; ST235; ST973; bla(VIM-2).