Antibiotic resistance patterns and associated genetic determinants among clinical isolates of Pseudomonas aeruginosa from a tertiary hospital in southern Iraq

Objective: To evaluate antibiotic resistance patterns and investigate the distribution of the carbapenemase‑associated gene blaOXA‑23 and the biofilm‑associated gene algD among clinical isolates of Pseudomonas aeruginosa recovered from patients at a tertiary hospital in Southern Iraq. Methods: A cross‑sectional study was conducted from November 2025 to April 2026 at Al‑Nasiriyah Teaching Hospital. A total of 120 P. aeruginosa isolates were collected from clinical specimens (burned tissue, sputum, urine, bronchoalveolar lavage, and others). Antimicrobial susceptibility was tested against 14 agents using the VITEK 2 system. Isolates were categorised as non‑MDR, MDR, XDR, and pandrug‑resistant (PDR). PCR was used to detect blaOXA‑23 and algD. Statistical analysis included chi‑square tests, with Cramér’s V for effect sizes. Results: PDR isolates were most prevalent (33.3%), followed by XDR (24.2%), non‑MDR (23.3%), and MDR (19.2%). Burned tissue yielded the highest proportion of PDR (n=18). Resistance rates were alarmingly high for ceftazidime (78.3%), cefotaxime (73.3%), and carbapenems (≈50%). algD alone was detected in 42.5% of isolates, blaOXA‑23 alone in 15.8%, and co‑occurrence in 22.5%. Significant associations were found between resistance patterns and specimen type (p<0.01, Cramér’s V=0.31), hospitalisation status (p<0.01, V=0.36), and age group (p<0.05, V=0.24). Conclusions: The high prevalence of MDR, XDR and PDR P. aeruginosa in clinical samples underscores the urgent need for integrated surveillance. The co‑occurrence of blaOXA‑23 and algD in highly resistant isolates suggests a synergistic interplay between carbapenemase activity and biofilm‑mediated protection.