Evaluation of the efficacy of colistin in inhibiting Pseudomonas aeruginosa isolated from clinical specimens and constructing its phylogenetic tree

Background: Antibiotic resistance has become a major global public health concern, largely due to the rapid ability of P. aeruginosa to adapt to widely used antimicrobial agents. Colistin, once considered a final therapeutic option for managing infections caused by Gram-negative bacteria, has gained renewed attention as resistance to other antibiotics continues to rise. Objective: This study aimed to assess the effectiveness of colistin in inhibiting P. aeruginosa and determine the genetic relationships among local isolates by constructing a phylogenetic tree, as well as comparing these local isolates with global isolates. Methodology: A total of 140 burn patient swabs were collected, identified, and tested for antimicrobial susceptibility using by VITEK 2 system. DNA from isolates was extracted, amplified by PCR, sequenced by Macrogen (Korea) and construct a phylogenetic tree using the Neighbor-Joining method. Results: Of the 140 specimens, 118 (84.3%) were culture-positive, including 60 isolates of P. aeruginosa (50.8%), while 22 samples (15.7%) showed no bacterial growth. Colistin demonstrated the highest susceptibility rate at 78%. The OprM gene was identified in 21 isolates (35%). Phylogenetic analysis of the OprM gene revealed that some local isolates clustered closely together, indicating they may have descended from a recent common ancestor. In contrast, other isolates showed greater genetic divergence The analysis also showed a clear genetic separation between local and global P. aeruginosa isolates. Statistical analysis demonstrated significant associations between the presence of the oprM gene and antibiotic resistance profiles. Conclusion: P. aeruginosa was the predominant pathogen in burn patients, and no antibiotic showed complete effectiveness. While some isolates remained sensitive to colistin, others were fully resistant. The OprM gene was identified in 21 isolates and was associated with increased antibiotic resistance.