Detection of carbapenem resistance mechanisms in difficult-to-treat Pseudomonas aeruginosa clinical isolates from a tertiary care hospital in Egypt.

BACKGROUND: The increasing incidence of carbapenem-resistant Pseudomonas aeruginosa (CRPA) poses a significant global health concern, particularly with the emergence of difficult-to-treat resistance (DTR), which seriously restricts therapeutic options. Therefore, we aimed to characterize DTR-PA isolates among the studied CRPA; regarding their resistance mechanisms to carbapenems and their antimicrobial susceptibility profiles. METHODS: Fifty-two non-duplicate CRPA isolates were collected from clinical specimens. Antimicrobial susceptibility testing was performed using disc diffusion and VITEK2 compact system. Isolates were classified as multidrug-resistant P. aeruginosa (MDR-PA), extensively drug-resistant P. aeruginosa (XDR-PA), and DTR-PA. Conventional PCR was used to detect carbapenemase genes (blaNDM, blaVIM, blaIMP, blaKPC, and blaOXA-48). Quantitative real-time PCR (qRT-PCR) identified the over expression of efflux pump genes (mexB, mexY) and the down regulation of outer membrane porin (oprD) gene. RESULTS: Fifty-two (52) CRPA isolates were categorized according to resistance phenotype into three main groups where 46% were identified as DTR-PA, 38% as XDR-PA, 8% as MDR-PA and 8% remained uncategorized. In DTR-PA, carbapenemase genes were detected in 92% of isolates with blaNDM being the most prevalent (75%), followed by blaVIM (54%) and blaOXA-48 (38%). Co-existence of multiple carbapenemase genes was common. Efflux pump mechanism was the most common mechanism of resistance as overexpression of MexB and MexY was observed in 98% and 71% of isolates, respectively, whereas downregulation of oprD was detected in 92%. The DTR-PA phenotype demonstrated the least sensitive profiles and most of the isolates (92%) were positive to all the studied resistant mechanisms (carbapenemase production, overexpression of efflux pump, and porin loss) with a statistically significant association (P = 0.001). CONCLUSIONS: Difficult to treat Pseudomonas aeruginosa is highly prevalent among CRPA isolates in our setting and is caused by multiple resistance mechanisms, particularly blaNDM carriage, efflux pump overexpression, and oprD downregulation. These findings underscore the urgent need for enhanced molecular surveillance and antimicrobial stewardship to limit further dissemination of highly resistant Pseudomonas aeruginosa (P. aeruginosa) iaolates. Future studies utilizing the DTR-PA definition are needed, as this category highlights the most resistant CRPA isolates with maximum resistance profiles that most likely to pose clinical challenges.