Evaluation of the Antibiofilm Activity of Cathelicidin LL-37 on Methicillin-Resistant Staphylococcus Aureus Strains Isolated from Patients with Urinary Infections

Abstract

Background: LL-37 peptide as a human Cathelicin is secreted in urinary tract and plays an important role in eradication of urinary infections with its antibiofilm activity. This study aimed to evaluate the antibiofilm activity of the human Cathelicidin LL-37 against biofilm-producing methicillin resistant Staphylococcus aureus (MRSA) isolates. Methods: During 2023-2025, 173 non-duplicate urinary isolates were collected from patients in a Tehran clinical laboratory and screened for MRSA using phenotypic methods and PCR targeting nucA, mecA, and mecC. Biofilm formation was first assessed on Congo red agar and then quantified by microtiter plate assay. Antimicrobial susceptibility was determined by disk diffusion per CLSI guidelines, while vancomycin MICs were measured using broth microdilution. Biofilm-associated genes, SCCmec and ccr types, and prophage patterns were identified by multiplex PCR. MICs of LL-37 were determined by broth microdilution, and sub-MIC levels were tested for inhibitory and disruptive effects on biofilm formation. Findings: Among all 173 MRSA isolates, 61 (35) were biofilm-positive. Genes icaA and icaD were detected in >80 of isolates. Prophage SGF and its subtypes were universal. SCCmec typing revealed that 79 of isolates (types I–III) were hospital-acquired (HA-MRSA) and 72 were multidrug-resistant. LL-37 demonstrated MIC values ranging from 32 to 512 μg/mL depending on biofilm strength. Sub-MIC concentrations significantly reduced biofilm formation (46-56) and disrupted pre-formed biofilms (48–67). Conclusion: LL-37 demonstrated robust antibiofilm activity against MRSA isolates and may represent a promising adjunct or alternative therapeutic option for biofilm-associated UTIs. © 2026, Isfahan University of Medical Sciences(IUMS). All rights reserved.