Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 17 2 2025 04 05 246 252 Rasha El-Mahdy Department Medical Microbiology and Immunology, Faculty of Medicine, Mansoura University, Mansoura, Egypt Ahmed Mostafa Department Medical Microbiology and Immunology, Faculty of Medicine, Mansoura University, Mansoura, Egypt Nora El-Tantawy Department Public Health, Faculty of Applied Medical Sciences, Al-Baha University, Al-Baha, Saudi Arabia; Department Medical Parasitology, Faculty of Medicine, Mansoura University, Mansoura, Egypt Raghdaa Shrief Department Medical Microbiology and Immunology, Faculty of Medicine, Damietta University, Damietta, Egypt 2024 09 05 2025 01 29 Background and Objectives: Increased Pseudomonas aeruginosa antibiotic resistance limits treatment options and is associated with a higher level of mortality and mordacity. The purpose of this research was to identify class 1 and 2 integrons, carbapenemase, SHV, and TEM genes in extensively drug-resistant (XDR) P. aeruginosa isolated from infected burns and evaluate their in vitro cefiderocol activity. Materials and Methods: By using the disc diffusion method, the antimicrobial susceptibility of 110 P. aeruginosa isolates collected from infected burns were evaluated. XDR P. aeruginosa were screened phenotypically for carbapenemase and extended spectrum β-lactamases (ESBLs) production. Both MIC Test Strip and disc diffusion were employed to test the cefiderocol susceptibility. PCR was used to assess carbapenemase, SHV and TEM genes and integrons class 1 and 2. Results: From the 110 P. aeruginosa, 54 isolates (49%) were XDR. TEM gene was detected in 35 isolates. Among XDR isolates, carbapenemase genes were detected in 31.5%, with NDM being predominant Thirty XDR isolates had class1 integrons. All isolates were sensitive to cefiderocol and its MIC50/MIC90 was 0.5/1.5mg/L (range 0.064-1.5mg/L). Conclusion: Nearly half the P. aeruginosa isolates from burn infections were extensively drug-resistant. Cefiderocol's in vitro activity demonstrated that it is a promising therapy alternative for treating extensively drug-resistant P. aeruginosa in burn patients. https://ijm.tums.ac.ir/index.php/ijm/article/view/5029 https://ijm.tums.ac.ir/index.php/ijm/article/download/5029/1763