Carbapenems are often described as the most effective weapon against infections provoked by multi-drug-resistant strains especially those belonging to the group of non-fermenting bacteria as Pseudomonas . The main mechanisms leading to resistance are the hyperexpression of some of the efflux pumps belonging to the Resisto-Nodular Division (RND) and the lower expression of the transmembrane receptor OprD sometimes in combination with excessive production of the intrinsic AmpC. Carpanemases are assumed to play a secondary role. The aim of this study was to determine the exact mechanisms of carbapenem resistance in Pseudomonas aeruginosa isolates from the biggest Bulgarian hospital “St. George”, Plovdiv, Bulgaria. We examined 43 clinical isolates resistant to imipenem and/or meropenem collected from different patients’ samples from our University hospital. No metallo-enzyme production was detected. The increased expression or hyperexpression of MexXY-OprM efflux pump was observed as a main mechanism of resistance. In most cases it was combined with lower expression or lack of OprD with or without MexAB-OprM hyperexpression. No excessive production of AmpC was detected in comparison with the reference ATCC 27853 Pseudomonas aeruginosa strain. In conclusion the increased expression or overexpression of MexXY-OprM efflux pumps is the leading cause of carbapenem resistance in our isolates Pseudomonas since it was detected in 94% of the examined bacteria.
Key words: carbapenem resistance, efflux pumps, OprD, AmpC, gene expression
Topic: MEDICINE