A Pilot Study on the Effect of In Vitro-Induced Antibiotic Resistance on Biofilm Formation by Uropathogenic Escherichia coli

Biofilm formation by uropathogenic Escherichia coli contributes to antibiotic resistance and the persistence of urinary tract infections. Whether biofilm formation is an intrinsic characteristic of UPEC or an adaptive response to antibiotic stress remains unclear, as does whether such adaptation is a generalized response to antibiotic exposure or is antibiotic-specific. This pilot study aimed to mimic the natural emergence of antibiotic resistance through repeated exposure of an antibiotic-susceptible UPEC isolate to selected antibiotics and subsequently evaluate changes in its biofilm-forming capacity in vitro. Three fully susceptible clinical isolates were screened against predefined inclusion criteria; the single isolate satisfying both criteria (14244) was exposed to sub-minimum inhibitory concentrations of amoxicillin and trimethoprim to generate antibiotic-resistant phenotypes. A fourfold increase in biofilm production was observed in the amoxicillin-resistant derivative, whereas no significant change was detected in the corresponding trimethoprim-resistant derivative compared to the parental antibiotic-sensitive isolate. These findings suggest that enhanced biofilm formation accompanying antibiotic resistance is an antibiotic-specific response rather than a universal adaptive mechanism. As a single isolate and one evolved lineage per agent were used, and as the resistance mechanisms were not characterized molecularly, the findings are hypothesis-generating; further studies employing multiple isolates, parallel evolutionary lineages, serotyping and molecular approaches are required to confirm the effect and elucidate the underlying mechanisms.