# Biofilms: Novel Strategies Based on Antimicrobial Peptides
## 4 Nanoparticles Coated with AMPs
[59] studied a highly cationic peptide PuroA (FPVTWRWWKWWKG-NH\({}_{2}\)), derived from the tryptophan-rich domain of wheat puro indoline proteins, chosen because of its broad spectrum of antimicrobial activity [16]; the peptide was conjugated with a colloid BCC layer as a suitable platform with inherent nano-/microstructures and topographies for covalent immobilization  
Figure 2: Coating of nanoparticles with antimicrobial peptides is a promising strategy to overcome the drawbacks of the nanoparticles and peptides themselves and improve their action with a synergistic effect. Moreover, the conjugation may affect the peptide properties and the design of new antimicrobial nanomaterials is required. of AMPs. The results showed a substantial increase of the anti-biofilm properties of PuroA-modified BCCs compared to the activity of unbound PuroA demonstrating also that changes in topography affect bacterial attachment profiles and growth. To date, comprehensive studies of AuNPs on bacteria have rarely been carried out and very little is known about the biological effects of AuNPs conjugated to AMPs [60; 61]. [PERSON] et al. identified a derivative of the frog skin AMP esculent-1a, esculent-1a(1-21)NH2[Esc(1-21)], GIFSKLAGKKIKNLLISGLKG-NH2, corresponding to the first 20 residues of esculent-1a, with a strong activity against both free-living and sessile forms of either reference or clinical isolates of _P. aeruginosa_[61]. Esc(1-21)-coated AuNPs were tested for their antibiofilm activity; when used against the sessile form of _P. aeruginosa_, 50% of the biofilm cells was killed within 2 h treatment at a peptide concentration of 0.171 M which was only two-fold higher than the MBC50, and about 17-fold lower than the MBEC 50 of the free peptide. Therefore, the frog skin AMP esculent-1a conjugated to AuNPs via PEG linker, demonstrated a remarkably improved antibacterial activity compared to the free peptide without being toxic to human cells. This is likely due to the significant quantity of Esc(1-21) present on the surface of AuNPs@PEG, regardless of its orientation, and to the high concentration of AuNPs@Esc(1-21) on the bacterial surface as well as to the prolonged peptide bioavailability, being less accessible to bacterial proteases. The functionalized AuNPs@Esc(1-21) also presented a membrane perturbing activity as a plausible mechanism of bacterial killing. [PERSON] et al. [62] reported that the antimicrobial activity of QDs is enhanced by the functionalization with the antimicrobial peptide indolicidin (QDs-Ind) against _S. aureus_ (ATCC 6538), _P. aeruginosa_ (ATCC 1025), _E. coli_ (ATCC 11229), and _Klebsiella pneumoniae_ (ATCC 10031), while the ecotoxicity decreases compared to the QDs and indolicidin separately using an ecotoxicological battery of test systems and indicators able to detect different effects using a variety of end points [62]. [PERSON] et al. [63] studied the efficacy in vitro of a nanocomposite of AuNPs coated with indolicidin (AuNPs-indolicidin) in both preventing cell adhesion and eradicating the developed biofilms of some _Candida_ clinical isolates and ATCC strains showing an enhanced indolicidin activity likely related to an enhanced stability of the nano-complex towards protease degradation occurring in the matrix and/or inside cells. [PERSON] et al. [64] showed that RRP9W4N covalently attached on the elastin-like polypeptide (ELP) films had anti-biofilm activity toward _S. epidermidis, S. aureus_, and _P. aeruginosa_, and moreover, the stability of covalently attached AMP in human serum was highly increased showing high activity up to 24 h [18]. [PERSON] et al. [65] designed two hybrid AMPs, KG18 and VR18, from the parent peptides VG13P and WR17 [19]. These chimeric peptides display increased and broad-spectrum activity compared to their parents; moreover, conjugation of ultra-small tungsten disulfide (WS2) QDs to these peptides was performed to further increase their antimicrobial activity.