[Antibiotic Susceptibility Profile and Biofilm Formation in Sequential Chronic Pseudomonas aeruginosa Isolates from Pediatric Patients with Cystic Fibrosis].

Cystic fibrosis (CF) is a genetic disorder that causes chronic infections due to the buildup of thick mucus in the airways. Pseudomonas aeruginosa is a common and significant pathogen in CF patients, contributing to long-term infections and colonization. This study aimed to evaluate and compare the antibiotic susceptibility patterns and biofilm-forming capacities of sequential P.aeruginosa isolates recovered from respiratory tract specimens of pediatric cystic fibrosis (CF) patients. Sequential chronic P.aeruginosa isolates (n= 80) were obtained from respiratory samples of CF patients who were prospectively monitored at the Hacettepe University İhsan Doğramacı Children’s Hospital CF Unit between 2021 and 2023. Identification of the bacteria to the species level was performed using MALDITOF MS and confirmed by conventional methods. Antibiotic susceptibility testing was conducted by broth microdilution and gradient test methods according to EUCAST recommendations. Antibiotic resistance genes (blaVIM, blaIMP, blaNDM, blaKPC) were investigated by PCR. Biofilm formation was evaluated using the crystal violet microtiter plate assay. The most frequently observed systemic manifestations accompanying CF were exocrine pancreatic insufficiency (n= 58) and bronchiectasis (n= 44). In addition to P.aeruginosa, co-isolation of other pathogens was detected in 56 patients, including methicillinsusceptible Staphylococcus aureus (n= 46), methicillin-resistant S.aureus (n= 31), Acinetobacter spp. (n= 2), and nontuberculous mycobacteria (n= 2). The highest antibiotic resistance rate among P.aeruginosa isolates was observed against ceftazidime (3.75%), while the lowest resistance was detected against colistin (1.25%). Resistance to tobramycin, meropenem, and levofloxacin was identified at a rate of 2.5%, whereas no resistance to ciprofloxacin was detected. The most prevalent antibiotic resistance gene was blaVIM, detected in 12.5% of the initial isolates and 10% of the subsequent isolates. None of the isolates harbored blaKPC, blaIMP, or blaNDM genes. Biofilm formation was observed in 77.5% of the initial isolates and 73.7% of the subsequent isolates. Quantitative analysis revealed biofilm formation in 59 (73.7%) of the 80 sequential isolates, with 11 (18.6%) classified as strong biofilm producers, 33 (55.9%) as moderate biofilm producers and 15 (25.4%) as weak biofilm producers. In conclusion, our results indicate that P.aeruginosa isolates exhibited a high biofilm formation capacity in CF patients, while antibiotic treatment played a limited role in bacterial eradication. The study revealed that sequential isolates did not demonstrate significant alterations in biofilm production or antibiotic resistance patterns over time. The persistence of P.aeruginosa isolates with similar antibiotic susceptibility and biofilm formation capacities in CF patients underscores the necessity of performing anti-biofilm susceptibility testing and developing novel anti-biofilm therapeutic strategies to improve bacterial eradication.