Control of extensively drug-resistant Pseudomonas aeruginosa co-harboring metallo-ß-lactamase enzymes with oprD gene downregulation.

PURPOSE: to study control and treatment of infection with extensive drug-resistant carbapenem-resistant Pseudomonas aeruginosa (XDR-CRPA). METHODS: Eleven Pseudomonas aeruginosa (XDR-CRPA) strains used in this study were isolated from a clinical sample, identified, and antibiotics susceptibility recorded in a previous study. Real-time PCR (RT-PCR) was performed to determine the expression level of the OprD gene. Besides, a checkerboard technique was performed to assess the effect of polymyxin-B (POX), colistin (COL), rifampicin (RIF), imipenem (IPM), and meropenem (MEM) during 2 and 3- dimensional antibiotic combinations. Further, the time-kill study was determined for the most potent combination against four representative strains, log10 changes of viable cell counts were expressed as their mean value (±SD) values. RESULTS: Molecular analysis by Real-time PCR revealed that the diminished expression level of OprD mRNA was overwhelming to various degrees. The checkerboard method demonstrated that the relevant synergism was achieved in 90.9% of strains for both carbapenem antibiotics during the triple combinations. While an additive effect was noted for all the dual regimen assays. Regarding time-kill experiments, a remarkable bactericidal effect with [99.9% killing rate] was observed toward only one strain whilst a bacteriostatic attitude was proven with ≥95% bacterial eradication against the three remaining strains. CONCLUSIONS: These findings underscore the promising implications of these combinations for treatment against XDR-Pseudomonas aeruginosa even they are resistant to carbapenems due to multiple mechanisms of action.