Investigation of Carbapenem resistance mechanisms by phenotypic and molecular methods in Pseudomonas aeruginosa strains isolated from blood culture

Objective: Carbapenem-resistant Pseudomonas aeruginosa (CRPA) is considered an important infection agent all over the world. This study aimed to investigate the mechanisms associated with carbapenem resistance in P. aeruginosa isolates grown in blood culture. Methods: CRPA isolates grown from blood samples were included in our study. Carbapenem minimum inhibitor concentration values were determined by the broth microdilution method. The carbapenem inactivation method was used to detect carbapenemase production and the polymerase chain reaction was used to investigate carbapenemase genes. Disc antagonism test was performed for detection of inducible AmpC β-lactamase. Overproduction of the efflux pump was determined by the broth microdilution method using the efflux pump inhibitor phenylalanine-arginine β-naphthylamide and by real-time polymerized chain reaction (RT-PCR) of various efflux pump genes (mexB, mexD, mexF, mexY). Expression levels of the porin protein gene oprD were examined by RT-PCR. Results and Conclusions: 48 CRPA isolates isolated from blood samples were included in the study. All the isolates were resistant to imipenem, 97,9% were resistant to doripenem, 75% were resistant to meropenem and half were found to be multidrug resistant. The presence of carbapenemase was detected phenotypically in 7 of the isolates (14,6%), and the blaVIM gene was found, while other carbapenemase genes could not be detected. Inducible AmpC β-lactamase was detected in 23 (47,9%) of the isolates. Overexpression of the efflux pump was detected phenotypically in 35 (72,9%) of the isolates; Overexpression of the efflux pump gene mexY was detected in 36 (75%), mexB in 5 (10,5%), mexF in 5 (10,5%) and mexD in 1 (2%) of the isolates. No significant decrease in the expression level of the oprD gene was detected in any of the isolates.