Carbapenem resistance mechanisms in Pseudomonas aeruginosa: alterations of porin OprD and efflux proteins do not fully explain resistance patterns observed in clinical isolates

Abstract

Imipenem resistance in Pseudomonas aeruginosa is considered to be associated with loss of the porin OprD combined with activity of chromosomal beta-lactamase (AmpC), while overexpression of multidrug efflux pumps is considered to confer meropenem resistance. Carbapenem resistance can also result from production of metallo-beta-lactamases. Transcription of oprD and efflux pump genes mexB, mexY and mexF was analysed in 23 clinical isolates of P. aeruginosa by quantitative RT-PCR. oprD was sequenced in all, and mexR, regulator of efflux pump MexAB-OprM, in selected isolates. Four isolates that were imipenem susceptible had significant reduction of oprD mRNA and presence of oprD mutations causing frameshift or translational stop. In strains only resistant to imipenem no significant difference in transcription of oprD was observed between low-level and high-level resistant isolates. The differences could not be explained by either pattern of oprD mutations. Increased transcription of mexB generally correlated well with meropenem resistance. One high-level meropenem-resistant isolate showed no significant change in mexB mRNA, but sequencing confirmed presence of a nalB mutation. Furthermore, one meropenem-susceptible isolate showed significant increase in mexB transcription, but no mexR mutations. In summary, our findings indicate that the resistance patterns observed cannot be fully explained by the currently described carbapenem resistance mechanisms.

Urinary Tract Infection: Aetiology and Antimicrobial Resistance Pattern in Infants From A Tertiary Care Hospital in Northern India

“…this is because carbapenem group is highly stable against β-lactamase and has an unusual property of causing a post antibiotic effect on gram-negative bacteria [16]. Due to its small molecular size it can overcome the poor permeability of β-lactams for Pseudomonas by efficient penetration through the porin, OMP-D [17].…”

The porin and the permeating antibiotic: a selective diffusion barrier in Gram-negative bacteria

“…Interestingly, the main cellular function of OprD is the passive uptake of basic amino acids as well as of small peptides 20 . In addition, overproduction of efflux pumps and other resistance mechanisms, together with the decrease of OprD expression, are involved in high-level imipenem and carbapenem resistance 62 .…”

Molecular Detection of blaVEB-1 Beta-Lactamase Encoding Gene Among Extended Spectrum B-Lactamase Positive Wound Isolates of Pseudomonas aeruginosa

“…Useful antibiotics include extended spectrum beta-lactamases (ESBL) and carbapenems, though multidrug-resistant isolates have emerged in hospital settings (2). Of several primary antibiotic resistant mechanisms, the down-regulation of membrane porins (OprD), in addition to increase in the expression of multidrug efflux pumps (MexAB-OprM) help intrinsic drug resistance (3). Novel beta-lactamases, including AmpC, extended spectrum beta-lactamases (ESBLs) and likewise several metallo beta-lactamases (MBLs) have emerged around the world as genetic encoding reservoirs responsible for the antimicrobial resistance among different gram-negative isolates (4).…”