PFGE-Based Evidence of Clonal Relatedness among Pseudomonas aeruginosa ST357 and ST274 Isolates from Cystic Fibrosis Patients at a Brazilian Amazon Referral Center.

INTRODUCTION: Persistent airway infection by Pseudomonas aeruginosa in cystic fibrosis (CF) is linked to internationally disseminated high-risk clones (HRCs). In a Brazilian Amazon CF cohort, we previously detected recurrent sequence types (STs) ST357 and ST274. Here, we evaluated whether repeated detections represented genetically distinct acquisitions or closely related strains. MATERIAL AND METHODS: We selected ST357 (n=7) and ST274 (n=8) isolates recovered in 2018 from 14 patients (15 isolates total) at a regional CF reference center. Clonality was assessed by PFGE. Disk diffusion (DD) susceptibility testing spanned nine antipseudomonal agents; for agents tested by both methods, results were compared with VITEK-2. RESULTS: ST357 isolates (7 patients) formed tight subclusters (>88% similarity) including two pairs of indistinguishable strains; overall similarity was 73.6%. ST274 (8 isolates, 7 patients) formed a cohesive cluster (80.2% overall) with one patient showing identical profiles five months apart. All isolates were MDR by DD. β-lactams showed broad non-susceptibility and method comparison revealed substantial discordance for several β-lactams. PFGE identified closely related inter-patient subclusters within ST357 and a cohesive inter-patient ST274 cluster. VITEK-2 yielded frequent susceptible classifications that were discordant with disk-diffusion results, particularly for β-lactams. Clinically consequential discordances should be interpreted cautiously. CONCLUSION: Findings support reinforcing CF-specific infection-prevention, implementing periodic genotypic surveillance, and expanding future work to longitudinal/environmental sampling.