Intermittent antibiotic exposure of Escherichia coli biofilms drives resistance in catheter-associated infection models.

The use of antibiotic lock therapy (ALT) to protect catheters from infection is still being debated due to its inconsistent effectiveness and the potential risk of promoting antibiotic resistance. Using an in vitro infection model of a pediatric venous access port, we demonstrated that 10 days of continuous therapy eradicates Escherichia coli biofilms in vitro without the emergence of antibiotic resistance. By contrast, an 8-h intermittent therapy used for infected parenteral nutrition patients rapidly selected low-level amikacin-resistant mutants both in vitro and in vivo in a clinically relevant rat model, primarily due to convergent fusA, sbmA, and cpxA mutations. Our findings indicate that intermittent dosing generates pulsed selective pressure, favoring the development of resistance mutants within spatially structured biofilm communities. This suggests that biofilms may act as evolutionary incubators, in which medical interventions could unintentionally influence adaptation outcomes. Furthermore, the low-level resistance developing in treated biofilms may be overlooked in clinical settings and contribute to the selection of high-level resistant mutants. Our study, therefore, underscores that, in addition to dosing, optimizing the timing of antimicrobial treatment could mitigate the emergence of resistance. These principles are applicable beyond catheters to any biofilm-related infections where short-term antibiotic exposure may impact microbial community adaptation.