Document Type : New and original researches in the field of Microbiology.
Authors
1
Department of Medical Microbiology and Immunology, Faculty of Medicine, Zagazig University, Egypt.
2
Department of Chest Diseases, Faculty of Medicine, Zagazig University, Zagazig, Egypt.
3
Department of Anesthesia, Intensive Care and Pain Management, Faculty of Medicine, Zagazig University, Zagazig, Egypt.
4
Department of Hepatology, Gastroenterology and Infectious Diseases, Faculty of Medicine, Zagazig University, Zagazig, Egypt.
Abstract
Background: Non-carbapenemase mediated mechanisms of carbapenem resistance in Pseudomonas aeruginosa (P. aeruginosa) are increasingly recognized. Ceftolozane/tazobactam (C/T) has emerged as a promising treatment option however resistance driven by structural alterations in Pseudomonas derived cephalosporinase (PDC) raises concern. Objective: to investigate the non-carbapenemase mediated mechanisms of carbapenem resistance and role of PDC alterations in C/T resistance. Methodology: One hundred and forty-two P. aeruginosa clinical isolates were tested for carbapenem resistance. The carbapenemase activity and the underlying carbapenemase genes were assessed in the carbapenem resistant (CR) isolates. Expression levels of outer membrane porin D, PDC and Efflux pumps genes were assessed by real time polymerase chain reaction in non-carbapenemase producing isolates. Susceptibility to C/T was tested by MIC test strips and blaPDC gene was sequenced in C/T resistant isolates to study alterations in PDC amino acid structure. Results: Thirty-eight (36.2%) of 105 CR P. aeruginosa isolates were non-carbapenemase producers. These isolates showed overexpression of PDC, by both phenotypic (16/38, 42.1%) and genotypic (23/38, 60.5%) methods, and of efflux pumps; mexB (29/38, 76.3%), mexD (14/38, 36.8%) and mexY (9/38, 23.7%), in addition to reduced expression of oprD (34/38, 89.5%). Twenty isolates (52.6%) showed non-susceptibility to C/T. PDC amino acid sequences from C/T resistant isolates showed G1D, T79A, V179L, D123E, L150R and G360A substitutions in different combinations, all located outside the substrate binding site of PDC. Conclusion: Porin deficiency, mexAB-oprM and PDC overexpression are the frequent drivers of carbapenem resistance in non-carbapenemase producing CR P. aeruginosa isolates. PDC amino acid alterations are likely not the cause of C/T resistance detected in these isolates.
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