Abstract

Objective: In this study, carbapenem minimum inhibitory concentrations (MICs) of Pseudomonas strains isolated from hospitalized patients with healthcare-associated infections, and metallo-β-lactamase (MBL) production in carbapenem-resistant strains were investigated.

Methods: 100 Pseudomonas isolates from patients with healthcare-associated infection, according to Centers for Disease Control and Prevention criteria were included in the study. Strains were identified by standard methods and VITEK® 2 (bioMérieux, Marcy l’Etoile, France). The antibiotic susceptibilities were investigated by Kirby-Bauer disk diffusion method according to Clinical and Laboratory Standards Institute criteria. Carbapenems’ MICs were determined using Etest® (bioMérieux, Marcy l’Etoile, France) for strains detected as carbapenem-resistant or intermediate by disk diffusion. MIC Test Strip® (Liofilchem, Roseto degli Abruzzi, Italy) MBL strips containing imipenem (4-256 μg/mL) and EDTA together with imipenem (1-64 μg/mL) were used in accordance with manufacturer’s recommendations for MBL detection in carbapenem-resistant strains.

Results: Isolation sites of 100 Pseudomonas strains were as follows: 37 from tracheal aspirate, 34 from urine, 17 from wound swab or abscess, 9 from blood, 2 from eye swab and 1 from pleural fluid. 99 of the strains were Pseudomonas aeruginosa, and 1 was P. putida. 65 of the strains were susceptible to all three antibiotics. 32, 20 and 16 of the strains were resistant to imipenem, meropenem, and doripenem and 2, 13, and 7 of them were intermediate to meropenem, imipenem and doripenem, respectively. 33 of the strains found resistant to at least one carbapenem were investigated for MBL existence. 29 (88%) of these 33 strains were MBL-positive.

Conclusions: In this study, we found an increased rate of carbapenem resistance and MBL enzyme activity is responsible in most (88%) of cases. Doripenem resistance was lowest and it may be due to doripenem’s nonavailability for clinical usage.