Phenotypic and genotypic study of carbapenem-resistant Pseudomonas aeruginosa strains isolated from hospitalized patients

Introduction: Nosocomial infections caused by Pseudomonas aeruginosa producing carbapenemases represent an important cause of morbidity and mortality among immunosuppressed patients. The aim of our study was to detect the production of metallo-carbapenemases (MBLs) by phenotypic methods and to detect the presence of the MBLs encoding genes (blaIMP and blaVIM) by PCR in P. aeruginosa strains isolated from hospitalized patients to the Regional Institute of Gastroenterology and Hepatology, Cluj-Napoca.

Material and methods: Between September 2014-February 2015, we tested thirty-eight P. aeruginosa strains resistant to carbapenems according to CLSI 2014 breakpoints, determined by Vitek^®2(BioMérieux),isolated from various clinical specimens. Phenotypic detection of the MBLs production was performed using the KPC/MBL Confirmation kit (ROSCO^®) and the MBL Etest^® IP/IPI (BioMérieux). We used the PCR method for detecting MBLs encoding genes: blaIMP, blaVIM.

Results: The strains were obtained from surgery (55.3%), ICU (15.8%) and gastroenterology wards (28.9%), isolated from pus (25.8%), tracheal secretion (22.7%), bile (13.6%), sputum (10.6%), blood (10.6%), other secretions (16.7%). These strains were resistant to multiple classes of antibiotics. By ROSCO^® method 28/38 strains (73.7%) were positive with imipenem ± dipicolinic acid (DPA) and 22/38 (57.9%) with meropenem ± DPA. Etest^® waspositive for the 28/38 strains (73.7%). 11 strains (28.9%) were positive for KPC with the screening method. We identified: 6 blaIMP+ (15.8%), 2 (5.3%) blaVIM+ and 4 blaIMP+/blaVIM+ strains (10.5%).

Conclusion: Both genes encoding MBL were found, alone or in combination. The increasing level of carbapenem resistance of these strains impose their routine testing to detect MBL.