Antimicrobial Activities of LL-37 Fragment Mutant-Poly (Lactic-Co-Glycolic) Acid Conjugate against Staphylococcus aureus, Escherichia coli, and Candida albicans

Abstract

Various peptides and their derivatives have been reported to exhibit antimicrobial activities. Although these activities have been examined against microorganisms, novel methods have recently emerged for conjugation of the biomaterials to improve their activities. Here, we prepared CKR12-PLGA, in which CKR12 (a mutated fragment of human cathelicidin peptide, LL-37) was conjugated with poly (lactic-co-glycolic) acid (PLGA), and compared the antimicrobial and antifungal activities of the conjugated peptide with those of FK13 (a small fragment of LL-37) and CKR12 alone. The prepared CKR12-PLGA was characterized by dynamic light scattering and measurement of the zeta potential, critical micellar concentration, and antimicrobial activities of the fragments and conjugate. Although CKR12 showed higher antibacterial activities than FK13 against Staphylococcus aureus and Escherichia coli, the antifungal activity of CKR12 was lower than that of FK13. CKR12-PLGA showed higher antibacterial activities against S. aureus and E. coli and higher antifungal activity against Candida albicans compared to those of FK13. Additionally, CKR12-PLGA showed no hemolytic activity in erythrocytes, and scanning and transmission electron microscopy suggested that CKR12-PLGA killed and disrupted the surface structure of microbial cells. Conjugation of antimicrobial peptide fragment analogues was a successful approach for obtaining increased microbial activity with minimized cytotoxicity.

Keywords: antimicrobial peptide; conjugation with poly (lactic-co-glycolic) acid; mutant peptide; scanning electron microscopy; transmission electron microscopy.

Figure 1

Predicted structures of LL-37, FK13, and CKR12. Fragmented sequence in LL-37 is underlined, and mutated residues in CKR12 are enclosed in the sequence of FK13. The predicted secondary structures are represented underneath the sequences as “H” for helical and “-” for random coiled structures.

Figure 2

Summary of synthesis of CKR12-PLGA conjugate via a cleavable disulfide linkage. CKR12 is shown as a cylinder.

Figure 3

Particle size (A) and zeta potential values (B) of CKR12-PLGA conjugate micelle.

Figure 4

Scanning electron microscopic images of S. aureus (A), E. coli (B), and C. albicans (C) cells in the absence (left panel) and presence (right panel) of 110 µM CKR12-PLGA.

Figure 5

Transmission electron microscope images of S. aureus (A), E. coli (B), and C. albicans (C) cells. The microorganisms are shown in the absence (left panel) and presence (right panel) of 61.3 µM CKR12-PLGA.

Figure 6

Schematic mechanisms of individual and self-assembled micelles of CKR12-PLGA against S. aureus, E. coli, and C. albicans.