OPRD1 and infection: The resistance mechanisms identified in carbapenem-resistant P. aeruginosa are generally the loss of the expression of the outer membrane protein OprD and overexpression of the efflux pumps (MexAB-OprM and MexCD-OprJ), the expression of intracellular β-lactamases, and the acquisition of multiple carbapenemase genes, etc. (34); however, these well-defined mechanisms have not yet been effective in solving the therapeutic challenges of infections with the clinical strains.