Correlation Between Antibiotic Resistance Phenotypes (MDR/XDR) and lasB/toxA Gene Expression in Clinical Pseudomonas aeruginosa Isolates

Background: Pseudomonas aeruginosa is a major opportunistic pathogen with increasing multidrug resistance (MDR) and extensive drug resistance (XDR), which pose significant clinical challenges. Virulence factors, such as elastase (lasB) and exotoxin A (toxA), contribute to its pathogenicity, but their relationship with resistance phenotypes remains underexplored.Objective: To evaluate the correlation between antibiotic resistance phenotypes (MDR/XDR) and lasB/toxA gene expression in clinical P. aeruginosa isolates. Methodology: A total of 300 clinical samples (burn swabs, urine, sputum, wounds, and ears) were collected from hospitals in Babylon City (January - March 2025). P. aeruginosa isolates (n=46) were identified via phenotypic, biochemical, and VITEK-2 testing, and confirmed by oprD PCR. Antibiotic susceptibility to 10 antibiotics was assessed using VITEK-2. The MDR/XDR classification system followed the CLSI/EUCAST guidelines. lasB and toxA genes were detected by PCR and their expression was quantified using RT-qPCR (2-ΔΔCt method). Results: The resistance was highest for piperacillin/ tazobactam (82.6%) and cefazolin (74%). Carbapenems (imipenem/meropenem) showed the lowest resistance (35–37%). The isolates were classified as susceptible (19.57%), MDR (36.96%), and XDR (43.48%). lasB and toxA were 45.65% and 71.74%, respectively. Both genes correlated significantly with the resistance profiles (lasB: χ²=4.36, P≤0.05; toxA: χ²=8.25, P≤0.01). toxA was upregulated in MDR isolates (1.6–3.3-fold) but downregulated in XDR isolates (0.36–0.73-fold). lasB expression varied in MDR isolates and was suppressed in XDR isolates (0.30–0.42-fold). Conclusion: A High MDR/XDR prevalence underscores antibiotic misuse in clinical settings. The correlation between toxA expression and resistance phenotypes suggests a role for toxA in adaptive mechanisms.