Antibiotic Susceptibility, Biofilm Formation, and Phylogenetics of <i>Pseudomonas aeruginosa</i> in Cystic Fibrosis Patients

Background and Aim: Pseudomonas (P.) aeruginosa is a Gram-negative bacterium that causes lung infection in cystic fibrosis (CF) patients by forming biofilms, which contribute to antibiotic resistance.The genetic diversity among strains could be important epidemiologically in the community of CF patients.This study investigated P. aeruginosa strains from CF patients' sputum, focusing on their antibiotic resistance, biofilm production, and genetic diversity to understand their epidemiological relations.Materials and Methods: Sixty-five samples of P. aeruginosa were isolated from CF patients with pulmonary infection symptoms (October 2023 to October 2024) admitted to Imam Khomeini Children's Hospital in Tehran.The antibiotic susceptibility patterns of these strains were examined using disk diffusion method (Kirby-Bauer), based on the CLSI standard.Moreover, to evaluate colistin susceptibility, broth microdilution (BMD) method was used.The strains' ability to produce biofilms was evaluated using a microtiter plate (MTP) assay.Finally, RAPD-PCR (Random Amplified Polymorphic DNA-Polymerase Chain Reaction) was employed for genetic analysis, using the short primer 272.Results: About 61.53% of P. aeruginosa strains exhibited multidrug resistance (MDR), while 30.7% of the strains exhibited extensively drug resistance (XDR) characteristics.The highest levels of antibiotic resistance were found against amoxicillin, amikacin, and cefepime.XDR and MDR strains exhibited strong biofilm-forming ability.The 65 studied strains were classified into 19 groups based on RAPD-PCR patterns, with six strains sharing similar genetic traits divided into four categories. Conclusion:The study showed elevation in antibiotic resistance in P. aeruginosa and established a strong connection between biofilm production and resistance.Some isolates exhibited similar genetic patterns, indicating possible crossinfection.