Phenotypic Changes in Antimicrobial Resistance in Repeated Isolates of <i>Pseudomonas aeruginosa</i>

Background: Pseudomonas aeruginosa infections have become a significant challenge due to the bacterium's resistance to many current antimicrobial agents.Repeated P. aeruginosa isolates also develop phenotypic changes in antimicrobial resistance after exposure to antimicrobials.This study aimed to explore changes in antimicrobial resistance patterns and resistance genes among patients with recurrent isolation of P. aeruginosa.Methods: The investigation of the status of phenotypic changes in antimicrobial resistance was based on antimicrobial susceptibility test results from the diagnostic test database over the last three years (2021-2023), including all samples from which P. aeruginosa was repeatedly isolated.Whole genome sequencing was performed on six pairs of P. aeruginosa isolates whose follow-up isolates acquired carbapenem resis- tance to detect changes in antimicrobial resistance genes.Results: Over the three-year study period, 18.6% (214/1,151) of patients experienced recurrent isolation of P. aeruginosa , with 29.0% (62/214) showing phenotypic changes in antimicrobial resistance.However, no additional resistance genes were identified in these isolates.Conclusions: The frequency of phenotypic changes in antimicrobial resistance was not negligible.Therefore, follow-up cultures and repeat antimicrobial susceptibility tests 3-4 days after P. aeruginosa isolation are strongly recommended.