Abstract
Bacteria are a common group of foodborne pathogens presenting public health issues with a large economic burden for the food industry. Our work focused on a solution to this problem by evaluating antibiotic activity against two bacteria (Listeria monocytogenes and Escherichia coli) of relevance in the field of foodstuffs. We used two approaches: (i) structural modification of the antimicrobial peptides and (ii) nano-vehiculisation of the modified peptides into polymer-coated liposomes. To achieve this, two antimicrobial peptides, herein named ‘peptide +2′ and ‘peptide +5′ were synthesised using the solid phase method. The physicochemical characterisation of the peptides was carried out using measurements of surface tension and dynamic light scattering. Additionally, nanoliposomes were elaborated by the ethanol injection method and coated with a cationic polymer (Eudragit E-100) through the layer-by-layer process. Liposome characterisation, in terms of size, polydispersity and zeta potential, was undertaken using dynamic light scattering. The results show that the degree of hydrophilic modification in the peptide leads to different characteristics of amphipathicity and subsequently to different physicochemical behaviour. On the other hand, antibacterial activity against both bacteria was slightly altered after modifying peptide sequence. Nonetheless, after the encapsulation of the peptides into polymer-coated nano-liposomes, the antibacterial activity increased approximately 2000-fold against that of L. monocytogenes.
Highlights
Foodborne illnesses have significant impacts on global healthcare systems
To contribute to solving this public health problem, alternative antibiotics have emerged, such as antimicrobial peptides (AMPs); e.g., Nisin is an AMP widely used as an additive to foodstuffs and is the only bacteriocin approved by FDA and European Union (E234) [2]
Peptide +2 was selected as a template sequence due to both, its reduced positive net charge and the presence of hydrophobic amino acids in the polar face of the helix, in order to explore the effect of increasing charge and hydrophilicity in that helix face on the biological activity, encapsulation ability and physicochemical properties
Summary
Foodborne illnesses have significant impacts on global healthcare systems. There is a growing concern regarding foodborne bacterial pathogens; the World Health Organisation (WHO) estimates that, in 2010, foodborne illnesses affected 600 million people globally and caused 420,000 deaths [1]. Other peptide structural properties, such as hydrophobicity, amphipathicity and secondary structure, play a pivotal role to achieve insertion into the microbial membrane [5]. Such structural properties can modulate the physicochemical characteristics of both the peptide and the antimicrobial activity [6,7]
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