Background: The human cathelicidin antimicrobial peptide (LL-37), a component of the host innate immune system, possesses the capability to combat bacterial biofilms. This study aimed to evaluate the effect of sub-MIC concentrations of LL-37 on biofilms formed by clinical uropathogenic Escherichia coli (UPEC) strains isolated from patients in Isfahan, Iran, during 2024.
Methods: A total of 247 suspected E. coli isolates were collected from patients and identified by standard biochemical tests, and finally confirmed using PCR by specific primers for tufA gene. Biofilm-forming ability was assessed using qualitative Congo Red Agar (CRA) and quantitative Microtiter Plate (MTP) methods, and the frequency of biofilm-associated genes was determined. The minimum inhibitory concentration (MIC) of the LL-37 cathelicidin (ProteoGenix France) was evaluated; and subsequently, the activity of LL-37 at sub-MIC concentrations on biofilm inhibition and destruction among six selected strains (strong, moderate, and weak biofilm-producers) was investigated.
Findings: Of the 204 confirmed strains, 57% were biofilm producers. The yedQ gene was detected in all biofilm-producing strains. The 12 µM concentration of LL-37 reduced biofilm formation in strong and moderate biofilm producers by 34-40% and 41-48%, respectively. Furthermore, this concentration disrupted pre-formed biofilms with an efficacy of 38-53%; however, the 6 µM concentration showed a limited effect (<10%) on weak biofilm producers.
Conclusion: The LL-37 peptide exhibits significant anti-biofilm activity at sub-MIC concentrations against clinical UPEC strains, particularly strong biofilm producers. These findings highlight the potential of LL-37 as an adjunctive therapeutic agent in the management of urinary tract infections.