Antimicrobial peptides are viewed as the latest weapon against bacteria especially in preserving food as well as possibly having extensive clinical benefits in fighting bacterial infection. They have also been shown to have activity against protozoa, fungi and yeasts, viruses and even tumour cells (Giuliani et al., 2007). Humans are able to digest these peptides using simple hydrolysis so there is plenty of promise (da Costa et al., 2015).
Bacterial infections still persist as a group of major diseases that have long been responsible for a high proportion of deaths throughout the world. Unfortunately along with the development of antimicrobials including antibiotics to tackle bacterial infection has come a time when bacterial strains have begun to literally fight back. The frequent use and misuse of antibacterials has meant that bacteria have started to develop resistance. Back in the 90s it was recognised that there was resistance to all kinds of antimicrobial drugs and this phenomenon is slowly growing worse (Gold & Moellering, 1996).
Antimicrobial peptides (AMPs) have broad antimicrobial activity. Many of them resist Gram-positive bacteria even though there are significant major differences between AMPs when it comes to their antimicrobial behaviour (Hancock and Scott, 2000).
The AMPs are small peptides of only 6 to 100 amino acids and less than 10 kDaltons in size. All are amphipathic and with their variable amino acid number, all different in length too.
They are part of the soluble host defense system. Being highly bioactive they are also part of the Mammalian Innate Immune Response (MIIR).
The mechanism of action is still being scrutinized. They produce cell death by affecting membranes and other machinery associated with metabolism and cell replication (Mankoci et al., 2019). It is thought that AMPs perforate the plasma membrane of bacteria and form ion channels which dissipate ion gradients and disrupt the cell membrane. there is a steady loss of nutrients and other intracellular content as a result with eventual destruction of the cell (Saint et al., 2003). They potentially have a similar action to antibiotics but the AMPs are more direct in their mechanism.
Bioactive peptides can also include whole proteins. Whey is a provider of 4 key proteins which in turn can be naturally hydrolysed are α-lactalbumin, β-lactoglobulin, lactoferrin, and lactoferricin (Park & Nam, 2015).
The protein α-lactalbumin found in human milk itself shows bactericidal properties against antibiotic-resistant strains of Streptococcus pneumoniae (Håkansson et al., 2000). Beta-lactoglobulin produces peptides that are inhibitory of the growth of L. monocytogenes and S.
aureus, inhibiting their growth by about 90% at concentrations of 10−20 mg/mL (Demers-Mathieu et al., 2013).
Casein, which forms 80% of milk protein yields antibacterial peptides. Two forms are known, αS1-casein and αS2-casein which can be hydrolysed. The hydrolysis product of αS2-casein has specific antibacterial properties against S. aureus, Sarcina spp., B. subtilis, Diplococcus pneumoniae, and Streptococcus pyogenes (Zucht et al., 1995). .
References
, . (1996). Antimicrobial-drug resistance. N. Engl. J. Med. 335 pp.1445–53 (Article).
Giuliani, A., Pirri, G. & Nicoletto, S. (2007). Antimicrobial peptides: an overview of a promising class of therapeutics. Open Life Sciences, 2, pp. 1-33
Håkansson, A., Svensson, M., Mossberg, A. K., Sabharwal, H., Linse, S., Lazou, I., Lönnerdal, B., & Svanborg, C. (2000). A folding variant of alpha-lactalbumin with bactericidal activity against Streptococcus pneumoniae. Molecular Microbiology, 35(3), pp. 589–600 (Article).
Hancock, R. E. W. & Scott, M. G. (2000). The role of antimicrobial peptides in animal defenses. Proceedings of the National Academy of Sciences of the United States of America,97, pp. 8856-8861.
Mankoci , S., Ewing, J., Dalai , P., Sahai, N., Barton, H. A. & Joy, A. (2019). Bacterial Membrane Selective Antimicrobial Peptide-Mimetic Polyurethanes: Structure-Property Correlations and Mechanisms of Action. Biomacromolecules, 20, pp. 4096-4106
Park, Y. W., & Nam, M. S. (2015). Bioactive peptides in milk and dairy products: A review. Korean Journal for Food Science of Animal Resources, 35(6), pp. 831–840
Zucht, H. D., Raida, M., Adermann, K., Mägert, H. J., & Forssmann, W. G. (1995). Casocidin-I: A casein-alpha s2 derived peptide exhibits antibacterial activity. FEBS Letters, 372(2-3), pp. 185–188
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