Abstract
Objectives: Cathelicidin LL37 represents one of the chemical defence components of bladder epithelial cells that include antimicrobial peptides, which also shown to have an important role in the mucosal immunity of the urinary tract by preventing adhesion of bacteria. This study aimed to determine the killing efficacy of LL37 compared to anti-biofilm activity against Staphylococcus aureus and Escherichia coli.
Methods: The 96-flat well microtiter plates were used for evaluation of killing rate by estimation of MIC-value to the clinical isolates of E. coli and S. aureus collected from patients with urinary tract infection. S. aureus ATCC 25923 and E.coli ATCC 25922 were investigated in this study. Biofilm formation on polystyrene surface was conducted by growing bacterial isolates on 96-flat well microtiter plates, stained with crystal violet. The bound bacteria were quantified by addition of ethanol 70% and measurement of the dissolved crystal violet absorbance at (OD630 nm) using ELISA reader.
Results: LL37 showed minimal inhibitory concentration (MIC) of 32 μg/ml against S. aureus and E. coli. The sub-MIC of LL37 was also able to eliminate about 31% and 34% of both S. aureus and E. coli, respectively. Anti-biofilm activity of LL37 showed biofilm inhibition at 1 μg/ml (1/32 MIC) to 16 μg/ml (1/2 MIC), which exhibited significant difference (p<0.001) against E. coli, whereas LL37 beyond 1 μg/ml showed significant inhibition (p<0.001) of biofilm against S. aureus.
Conclusion: The cathelicidin LL37 can be used as a broad-spectrum anti-biofilm agent rather than killing agent. J Microbiol Infect Dis 2015;5(1): 15-20

Key words: Cathelicidin LL37, MIC, biofilm, anti-adhesive, killing rateJ Microbiol Infect Dis 2015; 5(1): 15-20 doi: 10.5799/ahinjs.02.2015.01.0168